DELFTshipTM user manual

Version 3.3

Homepage www.delftship.net

E-mail info@delftship.net

Contact Delftship BVVinkenpolderweg 382952 AV AlblasserdamThe Netherlands

© Delftship BV 2006, 2007, 2008 The Netherlands

DELFTship

Table of Contents1. License and copyright.........................................................4

1.1 DELFTshipTM program...........................................................41.2 DELFTshipTM user manual....................................................41.3 DISCLAIMER OF WARRANTY...............................................4

2. Registering your software...................................................53. Background to surface modeling.........................................6

3.1 Surface modeling.....................................................................63.2 Subdivision surfaces................................................................6

3.2.1 Points........................................................................................73.2.2 Edges........................................................................................73.2.3 Faces.........................................................................................7

3.3 Subdivision explained..............................................................83.4 Guidelines to subdivision modeling.........................................9

4. Coordinate system adopted by DELFTship......................105. Using the hull modeling windows......................................13

5.1 Zooming, panning and rotating..............................................135.2 Selecting objects....................................................................135.3 Moving control points with the mouse...................................135.4 Manually modifying points.....................................................145.5 Drawing modes......................................................................145.6 Working with background images..........................................15

5.6.1 Visible......................................................................................155.6.2 Clear........................................................................................155.6.3 Load........................................................................................155.6.4 Save........................................................................................155.6.5 Origin.......................................................................................165.6.6 Set scale..................................................................................165.6.7 Transparent color.....................................................................165.6.8 Tolerance.................................................................................165.6.9 Blending..................................................................................16

6. File import ........................................................................176.1 Import Surface.......................................................................176.2 Import chines.........................................................................186.3 Table of offsets......................................................................196.4 Background images...............................................................23

7. Program preferences........................................................247.1 General..................................................................................247.2 Hullform..................................................................................247.3 Hydrostatics...........................................................................247.4 Report....................................................................................247.5 Tanks.....................................................................................247.6 Load cases.............................................................................24

8. Project settings..................................................................258.1 General..................................................................................258.2 Main dimensions....................................................................258.3 Hydrostatics...........................................................................268.4 Critical points.........................................................................268.5 Tanks.....................................................................................278.6 Load cases.............................................................................278.7 Longitudinal strength.............................................................278.8 Probabilistic damage stability................................................28

9. Edit options.......................................................................299.1 Undo......................................................................................299.2 Redo......................................................................................299.3 Delete.....................................................................................299.4 Point.......................................................................................29

9.4.1 Add..........................................................................................299.4.2 Align........................................................................................299.4.3 Collapse..................................................................................299.4.4 Fair points................................................................................309.4.5 Plane intersection....................................................................309.4.6 Intersect layers........................................................................309.4.7 Copy values.............................................................................319.4.8 Lock points..............................................................................319.4.9 Unlock points...........................................................................319.4.10 Unlock all points.....................................................................319.4.11 From markers........................................................................31

9.5 Edge.......................................................................................31

9.5.1 Extrude....................................................................................319.5.2 Split.........................................................................................329.5.3 Collapse..................................................................................329.5.4 Insert.......................................................................................329.5.5 Crease.....................................................................................32

9.6 Face.......................................................................................339.6.1 New.........................................................................................339.6.2 Invert.......................................................................................33

9.7 Curve.....................................................................................349.7.1 General information about control curves and fairing...............349.7.2 New.........................................................................................359.7.3 Fair..........................................................................................359.7.4 Convert to marker....................................................................35

9.8 Layer......................................................................................369.8.1 General layer information.........................................................369.8.2 Active layer color.....................................................................369.8.3 Auto group...............................................................................369.8.4 New.........................................................................................369.8.5 Delete empty...........................................................................369.8.6 Dialog......................................................................................37

10. Display............................................................................3910.1 Controlnet............................................................................3910.2 Control curves......................................................................3910.3 Interior edges.......................................................................3910.4 Show both sides..................................................................3910.5 Grid......................................................................................3910.6 Stations................................................................................4010.7 Buttocks...............................................................................4010.8 Waterlines............................................................................4010.9 Diagonals.............................................................................4010.10 Hydrostatic features...........................................................4010.11 Critical points.....................................................................4110.12 Leak points only.................................................................4110.13 Flowlines............................................................................4110.14 Normals..............................................................................4110.15 Curvature...........................................................................4110.16 Markers..............................................................................4210.17 Marker points.....................................................................4210.18 Tanks.................................................................................4210.19 Sounding pipes..................................................................4210.20 Transparent tanks..............................................................4210.21 Tank names.......................................................................4210.22 Curvature scale..................................................................42

11. Tools...............................................................................4311.1 Check model........................................................................4311.2 Move to baseline..................................................................4311.3 Remove negative.................................................................4311.4 Remove unused points........................................................4411.5 Extract critical points............................................................4411.6 Subdivide controlnet............................................................4411.7 Keel and rudder wizard........................................................4411.8 Markers................................................................................44

11.8.1 Import....................................................................................4511.8.2 Export....................................................................................4511.8.3 Delete....................................................................................45

11.9 Add box................................................................................4511.10 Add cylinder.......................................................................4511.11 Edit criteria.........................................................................46

11.11.1 Section.................................................................................4711.11.2 Freeboard............................................................................4711.11.3 Equilibrium angle.................................................................4711.11.4 Combined heel and trim angle..............................................4811.11.5 Area under the GZ curve......................................................4811.11.6 Value of max. GZ.................................................................4911.11.7 Angle of max. GZ.................................................................4911.11.8 Metacentric height................................................................4911.11.9 GM in damaged condition....................................................5011.11.10 Wind heeling criterion.........................................................5011.11.11 Passenger crowding angle.................................................5111.11.12 High speed turning angle...................................................52

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DELFTship

12. Transform........................................................................5312.1 Scale....................................................................................5312.2 Move....................................................................................5312.3 Rotate..................................................................................5312.4 Mirror....................................................................................5312.5 Hullform transformation.......................................................53

13. Tanks..............................................................................5513.1 General information about tanks.........................................5513.2 Edit.......................................................................................55

13.2.1 Adding a tank.........................................................................5613.2.1.1 Abbreviation......................................................5613.2.1.2 Group................................................................5613.2.1.3 Tank position.....................................................5613.2.1.4 Relative density................................................5613.2.1.5 Intact permeability.............................................5713.2.1.6 Damage permeability........................................5713.2.1.7 Non-buoyant.....................................................5713.2.1.8 Use FSC when slack........................................57

13.2.2 Adding a compartment...........................................................5713.2.2.1 Type of compartment........................................5713.2.2.2 Compartment position.......................................5813.2.2.3 Positive/negative...............................................5813.2.2.4 Trim at hull........................................................5913.2.2.5 Use all layers....................................................5913.2.2.6 Select................................................................59

13.2.3 Copy a tank or compartment..................................................5913.3 Tank arrangement...............................................................5913.4 Comparison of internal and external geometry...................6013.5 Overview..............................................................................60

14. Load cases......................................................................6114.1 General information about load cases.................................6114.2 Edit.......................................................................................61

14.2.1 Using the weight list...............................................................6314.2.2 Editing load cases..................................................................63

14.2.2.1 Add a new load case........................................6314.2.2.2 Modify the load case name...............................6314.2.2.3 Selecting a wind silhouette...............................6414.2.2.4 Adding weights..................................................6414.2.2.5 Modifying the different types of weights...........6414.2.2.6 Selecting a tank or a weight from the weight list........................................................................................6414.2.2.7 Add all tanks.....................................................65

14.2.3 Deleting a load case..............................................................6514.2.4 Copy a load case...................................................................6514.2.5 Solve a load case...................................................................6514.2.6 Show report...........................................................................6514.2.7 Interpreting results.................................................................6514.2.8 Bending moment and shear force calculations.......................66

14.3 Wind silhouette....................................................................6814.3.1 Adding a new wind silhouette.................................................6914.3.2 Modifying wind silhouette data...............................................69

14.4 Wind moment calculation....................................................6915. View................................................................................70

15.1 Intersections.........................................................................7015.2 Linesplan..............................................................................7115.3 Design hydrostatics.............................................................7115.4 Hydrostatics.........................................................................7115.5 Inclined hydrostatics............................................................7215.6 Crosscurves.........................................................................7315.7 Max VCG'.............................................................................7415.8 Plate developments.............................................................7415.9 Resistance...........................................................................76

15.9.1 Delft series.............................................................................7615.9.2 Kaper.....................................................................................76

15.10 Probabilistic damage stability............................................7716. Selection.........................................................................78

16.1 Selecting objects in DELFTship...........................................7816.2 Select all..............................................................................7816.3 Deselect all..........................................................................78

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DELFTship

1. 1. License and copyrightLicense and copyright

1.1 1.1 DELFTshipDELFTshipTMTM program. program.

Copyright © 2005-2008 Delftship BVDELFTship is copyrighted and all rights are reserved. The license for use is granted to the purchaser by DelftshipBV as a single user license and does not permit the program to be used on more than one machine at one time.Copying of the program to other media is permitted for back-up purposes as long as all copies remain in thepossession of the purchaser.

1.2 1.2 DELFTshipDELFTshipTMTM user manual user manual

Copyright © 2005-2008 Delftship BVAll rights reserved. No part of this publication may be reproduced, transmitted, transcribed, stored in a retrievalsystem, or translated into any language in any form or by any means, without the written permission of DelftshipBV. Delftship BV reserves the right to revise this publication from time to time and to make changes to thecontents without obligation to notify any person or organization of such changes.

1.3 1.3 DISCLAIMER OF WARRANTYDISCLAIMER OF WARRANTY

NO LIABILITY FOR CONSEQUENTIAL DAMAGES. In no event shall Delftship BV or the author of thisprogram or document be liable or responsible for any damages whatsoever (including, without limitation,incidental, direct, indirect and consequential damages, damages for loss of business profits, business interruption,loss of business information, or other pecuniary loss) arising out of the use or inability to use this product and itsattendant documentation, even if advised of the possibility of such damages. No Delftship BV distributor, or agent,or employee is authorized to make any modification, extension, or addition to this warranty.

No warranty. Any use by licensee is at the licensee's own risk. product is provided for use "as is" without warrantyof any kind. To the maximum extent permitted by law, the author disclaims all warranties of any kind, eitherexpress or implied, including, without limitation, implied warranties of merchantability, fitness for a particularpurpose and non infringement.

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DELFTship

2. 2. Registering your softwareRegistering your softwareAfter having installed the professional version (not the free version!) of DELFTship you first need to register yoursoftware in order to enable the printing and saving features. Registering is done by sending a registration code tosupport@delftship.net. The registration code is used to generate a license file which will be send to you by emailand must be placed in the program directory (default c:\program files\delftship ). Only then the software will be fullyfunctional. The license file depends on several hardware components available in your computer, so the softwareonly runs on the computer(s) where the registration code was generated. If you want to run the software on morethan one computer, for example on a PC and a laptop, DELFTship BV can provide you with an extra license onrequest. If you have made modifications to your computer's hardware you can also request a new license file.Extra licenses will be supplied on a “fair use” policy.You can find the registration code at the bottom leftcorner of the about window. The about window isaccessible from the main menu and is located underHelp => About...

The code consists of several groups of 4 characterseach. The groups are divided by spaces. You can eithertype the code manually into your email client, or copyand paste the code. The easiest way however is tosimply press the Send button displayed right next tothe registration code. A new email message will begenerated automatically with the registration code inthe body ready to be sent to Delftship BV.

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Illustration Illustration 2.12.1: The about window.: The about window.

DELFTship

3. 3. Background to surface modelingBackground to surface modeling

3.1 3.1 Surface modelingSurface modelingDELFTship uses a technique called surface modeling to completely define theouter shape of a ship. This technique involves “sculpting” the hull as if it were avery thin and flexible piece of cloth by pulling and shifting points. It is howevernot limited to the hull alone as we will see later. Decks, superstructures, masts,keels and rudders can be modeled this way too. The biggest advantage ofsurface modeling is that the model can be completely and accurately describedusing only a few points. Illustration 3.1 shows an example of a developable tugthat was created with only 54 points. Unlike other programs, DELFTship usessubdivision surfaces for this task. Compared to other types of surfacedefinition, subdivision surfaces give the designer more flexibility in designingany desired shape. But when you want to get the most of this technique it isimportant to have a basic understanding of some of its underlying principles.

3.2 3.2 Subdivision surfaceSubdivision surfacessA subdivision surface is a special type of spline-surface.Conventional modeling programs work with parametric splinesurfaces like B-Spline surfaces or NURB surfaces. These surfacesare completely defined by a set of control points. These are thepoints which the user can modify to control the shape of the surface.Any point on the surface can be directly calculated from thesecontrol points using a set of parametric formulas. The drawback ofthese parametric surfaces is that they always require a topologicallyrectangular grid of points. This grid in reality almost always followsthe shape of a hull, so it does not look like a true rectangular grid.But it always has say N points in the longitudinal direction and Mpoints in the vertical direction where both N and M might be anynumber equal to or larger than 2. On illustration 3.3 N=4 and M=4and the total number of control points equals 4*4=16. Usingparametric spline surfaces it is not possible to insert a single newpoint in the control grid. To maintain the rectangular topology anentire row of points have to be inserted as demonstrated onillustration 3.2. This results in having more control points thanactually needed or desired, and more control points means morework to the designer. Also very complex shapes cannot bemodeled using a single surface. But when using multiple surfacesthe designer is challenged with the difficult task of aligning thesesurfaces at their boundaries. It is often desirable to maintain asmooth transition along these boundaries. Each time one of thesesurfaces is modified, the adjacent surface has to be modified bythe user to maintain this smooth transition. To overcome theseproblems DELFTship makes use of subdivision surfaces.Subdivision surfaces also use control points as a modelinghandle, just like NURBS or B-Splines and they share the samemathematical background. The main difference however is thatthe formulas are no longer restricted to a rectangular grid ofpoints. The downside is that points on the surface can no longerbe directly calculated due to this different approach. Instead the original set of points (called the control mesh) isrefined and smoothed in a number of steps. Each step is called a “subdivision step”, hence the name subdivision

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Illustration Illustration 3.13.1: Surface modeling.: Surface modeling.

Illustration Illustration 3.23.2: Inserting a row or column.: Inserting a row or column.

Illustration Illustration 3.33.3: Parametric spline surface.: Parametric spline surface.

DELFTship

surfaces. Before explaining in detail how subdivision actually works it is important to know something about theinternal geometry of subdivision surfaces. The surfaces are build from the following three components:

3.2.1 3.2.1 PointsPointsPoints form the basis of the surface. In fact most of themodeling is done by moving points to different locations sincethis changes the shape of the surface. Additionally, new pointsmay be inserted or existing points can be removed. There aretwo different types of points:

● Ordinary points. These are any points other then cornerpoints. It is important to realize that these points have acertain offset to the resulting surface. This deviation is largerin surface areas with high curvature. It becomes smallerwhen more points and edges are inserted.

● Corner points are very specific points, usually connected to2 or more crease-edges. Just like a crease-edge can be used to specify that two faces have to be connected in adiscontinuous way, corner points may be used to do so with two adjacent edges. Corner points are the only type ofpoints actually located on the hull surface. Points where 3 or more crease-edges meet are automatically set to cornerpoints by the program. Corner points are displayed blue.

3.2.2 3.2.2 EdgesEdgesAll points are connected with lines which are called edges in subdivision surface terminology. Edges also can bedivided into two different categories:

● Boundary edges. These are edges which are located, just as the name suggests, on the boundary of the surface. Aboundary edge is characterized by the fact that it has always only 1 face attached to it. Examples of boundary edgesare the sheer line (if the ship is not fitted with a deck) or the centerline of the ship. The centerline, or profile, is in fact aspecial case. When defining the hull only its port side is created. So all edges on the center plane are boundary edgesas they have only one face connected to it. In reality the ship is symmetric, and when performing calculationsDELFTship creates a virtual symmetric ship by mirroring the model in the center plane.

● Internal edges. These are all other edges away from the boundary of the surface, and must always be shared by 2adjacent faces. Internal edges are drawn as dark gray lines. The two faces connected to an edge are joined smoothlyalong their shared edge. It is possible however to mark an edge as a crease-edge. When doing so, the two faces arejoined in a tangent-discontinuous way. In other words, crease-edges are used to define knuckle lines. A boundaryedge is in fact a specific case of a crease edge since there is no second face to make a smooth transition.

3.2.3 3.2.3 FacesFacesA face is a little piece of the entire surface (sometimes also called a patch) that is completely surrounded by edgesand is usually defined with 4 points. In some areas it is desirable to have less (or even more) points, but generallythe best results are obtained when most of the faces consist of 4 points. Faces are surrounded by edges wherethe type of edge determines how the faces should be connected to each other.

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Illustration Illustration 3.43.4: Points, edges and faces.: Points, edges and faces.

DELFTship

3.3 3.3 Subdivision explainedSubdivision explainedNow there is a basic understanding of the underlying geometry the process of transforming the control mesh intothe final hull surface will be clarified. Illustration 3.5 shows the process of one subdivision step.

● To the left the original control mesh of a beveled cube isvisible. The first step in the subdivision process is refiningthe mesh. This is done by inserting a new point in themiddle of each edge (called an edge-point).

● New points are also inserted at the center of each face(called a face-point) which has more than three points.For faces with three points each new edge-point isconnected with the new point of the previous edge, thuscreating 4 new triangles. All other faces are subdividedby connecting all surrounding edge-points to the face-point. This results in a refined mesh which still has the same shape as the original. This process is shownin the middle.

● Finally all the points in the surface are shifted to a new location in such a way that the refined surface issmoothed. This is called averaging in subdivision terms (right side).

If this process of subdividing is repeated several the resulting mesh will be very fine and smooth. The followingillustration shows the same beveled cube after a number of subdivision steps.

Illustration 3.7 shows the same control mesh, but this time anumber of edges have been marked as crease-edges (redlines). The result is a sharp knuckle line going around thecube. It is clearly visible that the faces on both sides of thecrease-edges are no longer joined smoothly.

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Illustration Illustration 3.53.5: One subdivision step.: One subdivision step.

Illustration Illustration 3.63.6: Original control mesh and resulting surface after 1, 2 and 3 subdivision steps.: Original control mesh and resulting surface after 1, 2 and 3 subdivision steps.

Illustration Illustration 3.73.7: Crease edges.: Crease edges.

DELFTship

3.4 3.4 Guidelines to subdivision modelingGuidelines to subdivision modelingIn theory almost any control mesh is valid, however when designing ships the fairness of the resulting surface is ofuttermost importance. In this paragraph some guidelines are given that will assist you in obtaining the best results.

● Use a regular grid whenever possible. A grid isconsidered regular if all faces consist of four points,and all points are connected to four edges and faces. Apoint on a boundary edge is considered regular if it has3 edges and two faces connected to it. Of course thisis not always possible. Triangular faces may be usedas a means to reduce the number of points in an area.5-sided faces, or 5 different 4-sided faces can be usedto increase the number of points. A truly regular gridwould look exactly the same as the B-spline surfacefrom illustration 3.3 on page 6.

● Always have two faces connected to all edges otherthan boundary edges. If more than two faces areconnected to an edge, that specific edge will be drawnthicker and in a light green color. This must be avoided at all cost as it messes up hydrostatic calculations.boundary edges are allowed, but once they become submerged hydrostatics will no longer be calculated.(see also paragraph 8.3 on page 26 and paragraph 11.1 on page 43 for leak points).

● Ensure that the normals of all the faces point outward (in the direction of the water). This is of crucialimportance since DELFTship calculates hydrostatics by integrating the enclosed volume at the back ofthe faces. If the normal of a face points inward, the volume outside the hull would be added to the totalvolume. By using the actual surface for hydrostatic calculations instead of a number of stations, a higheraccuracy is obtained compared to the conventional method of using cross sections. This is especially trueif the model has a heeling angle and/or trim, or is fitted with a superstructure. DELFTship can also checkthe direction of normals automatically. Automatic checking can be disabled in the project settings dialog asexplained in paragraph 8.3 on page 26.

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Illustration Illustration 3.83.8: Regular points.: Regular points.

Illustration Illustration 3.93.9: Example of a highly irregular grid where some of the: Example of a highly irregular grid where some of theirregular points have been pointed out by red arrows.irregular points have been pointed out by red arrows.

Illustration Illustration 3.103.10: Same ship with a more regular grid in the foreship.: Same ship with a more regular grid in the foreship.

DELFTship

4. 4. Coordinate systemCoordinate system adopted by DELFTship adopted by DELFTship

DELFTship uses the coordinate system as displayedon illustration 4.1. The aft perpendicular is alwayslocated at the origin of the coordinate system. The axishave the following directions with respect to the shipmodel:

● The X axis corresponds to the longitudinaldirection of the ship.

● The Y axis is oriented transversely. Positivevalues are located on port side.

● The Z axis is oriented vertically and pointsupward.

Positive values for heeling angles are also to portsidewhile for negative values the ship heels to starboardside.

Illustration 4.2 shows the most important reference lines:

● The aft perpendicular which is located at the origin (x=0.0).

● The forward perpendicular. The location is specified by the user in the project settings and must be a avalue greater than zero since the aft perpendicular is located at the origin. The length of the ship is definedas the distance between the two perpendiculars.

● The base line. The base line corresponds with the horizontal plane through the origin (z=0.0). All drafts aremeasured with respect to this baseline so it's important that the lowest part of the ship coincides with thisplane.

Draft is defined as (see illustration 4.3) :

● Draft aft: The distance measured along the aft perpendicular from the base plane to the intersection of thewater plane with the center plane.

● Draft forward: The distance measured along the forward perpendicular from the base plane to theintersection of the water plane with the center plane.

● (Average) draft: The average of both drafts =0.5* (TAft+TForward)

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Illustration Illustration 4.14.1: DELFTship coordinate system: DELFTship coordinate system

Illustration Illustration 4.24.2: Reference lines: Reference lines

DELFTship

These definitions are valid both in upright and heeled conditions. Note that in the event of large heeling angles andsmall values for the displacement this can lead to negative values for the draft as can be seen to the right ofillustration 4.3. The intersection of the water plane and the center plane is located below the base plane resultingin a negative value for the draft.

Trim is defined as the difference in draft at both perpendiculars (Illustration 4.4).

Trim =TForward-TAft

If the draft aft is greater than the draft forward the trim will be negative. So negative trim values indicate the ship istrimmed by the stern, while for positive trim values the ship is trimmed by the bow.

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Illustration Illustration 4.34.3: Draft measured when heeled.: Draft measured when heeled.

Illustration Illustration 4.44.4: Definition of trim.: Definition of trim.

DELFTship

Finally all values for the various hydrostaticproperties are measured with respect to the shipsmain axis with the ship in upright position.Illustrations 4.6 and 4.5 show a ship with trim anda ship heeled to port side. Rather than heeling theship the water plane is rotated instead. Alldimensions are measured along the three mainaxis that pass through the origin. Both illustrationsshow the presentation of the location of the centerof buoyancy in 3D space as an example. Thispresentation will be consistently used throughoutthe program.

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Illustration Illustration 4.64.6: Longitudinal and vertical measurements for a trimmed ship.: Longitudinal and vertical measurements for a trimmed ship.

Illustration Illustration 4.54.5: Transverse and vertical measurements for a heeled ship.: Transverse and vertical measurements for a heeled ship.

DELFTship

5. 5. Using the hull modeling windowsUsing the hull modeling windows

5.1 5.1 Zooming, panning and rotatingZooming, panning and rotatingAfter opening or starting a new model the program by default adds 4 windows. Each window has a different viewon the 3D hull. The area of the window where the model is drawn is called a viewport. These viewports alsoappear in several other windows, for example when viewing plate developments. Zooming and panning works thesame in all viewports used throughout the program.

Zooming can be done in different ways:

● Ctrl-A (zoom all) ● Move the mouse up or down while keeping the left button pressed.● Press Ctrl-I (zoom in) or Ctrl-O (zoom out)● Users having a mouse wheel may find it more convenient to zoom in or out using their mouse wheel.● By drawing a selection rectangle with your mouse.

Zooming is only allowed until the maximum zoom level has been reached. Zooming beyond this level is notpossible.

Panning is done by moving the mouse with the right button pressed.

If the viewport displays a perspective view then two scrollbars will be visible also, located below and to the right ofthe viewport. These scrollbars can be used to rotate and tilt the model in order to see your model from a differentviewing angle. Another more convenient way to rotate the model is keeping the middle mouse button (or mousewheel) pressed while dragging the mouse. This also works only in a perspective view.

5.2 5.2 Selecting objectsSelecting objectsSelecting objects is explained in paragraph 16.1 on page 78.

5.3 5.3 Moving control points with the mouseMoving control points with the mouseOne of the most important features when it comes to surface modeling is the ability to move points. In order to dothis the controlnet must be visible (see also chapter 10). Although it is possible to select points in a perspectiveview, the actual dragging of the point can only be done in the bodyplan view, profile view or plan view. Whiledragging a point all geometrical information is updated real-time. This includes intersection curves, control curves,flowlines and tanks, especially when the precision of the model is set to a high level this updating process mightbecome slow due to the amount of calculations involved. If it becomes too slow, try using a lower precision orturning off some of these objects in your display settings.

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DELFTship

5.4 5.4 Manually modifying pointsManually modifying pointsOnce a point is selected, the window from illustration 5.1 displays all the information forthat point, including the position of the point in 3D space. These properties can bealtered manually by typing the new values in the appropriate fields. In addition they canalso be altered relative to the current location by typing the character @ in front of thenumerical part. If for example the string @ -0.2 is entered in the field for the y-coordinate, then all the y-coordinates of all selected points will be decreased by 0.20.So the y-coordinate for the displayed point becomes 2.10-0.20=1.90. This is aconvenient way to shift a number of selected points.

Another way of moving points is by pressing the cursor keys in the bodyplan, profile or plan view. The active pointmoves a certain distance in the direction of the arrow key that was pressed. The magnitude of this distance, called“incremental distance” is visible on the status bar of the program, next to the amount of undo memory that is inuse. By clicking on the text displaying the value for the incremental distance a window is opened in which a newvalue for the incremental distance can be specified. Another and faster way is to press either the + or – key. Theincremental distance is then changed by 10%.

Finally the black arrows displayed next to each input field on the form can be used to modify the values by thesame incremental distance as mentioned above. Chapter 4 on page 10 describes the coordinate system used byDELFTship.

5.5 5.5 Drawing modeDrawing modessDELFTship has several ways of presenting the hull. These drawing modes are accessible from the popup-menuunder the right mouse button.

● Wireframe (Ctrl-W). Only the points, lines and edgesare drawn. Any objects, such as tanks for example,are drawn using line representations.

● Shade (Ctrl-F). The surfaces are drawn in a solidcolor, lines and curves are drawn on top of thesurfaces. Submerged areas of surfaces canoptionally be displayed using a different color.

● Developability check (Ctrl-D). The surfaces areshaded again, only this time areas of the surface thatare developable are colored green while parts thatare not developable are colored red. More aboutdevelopable surfaces can be found in paragraph9.8.6 on page 37 and paragraph 15.8 on page 74.

● Gaussian curvature (Ctrl-G), used to check thefairness of a surface. The model is drawn using arange of colors, based on the discrete Gaussiancurvature in each point of the subdivided surface. Most surfaces are curved in two directions, called theprincipal curvature directions. The Gaussian curvature is the product of these two principal curvatures.Now when it comes to the sign of the Gaussian curvature there are 3 possibilities :

• Negative Gaussian curvature. One of the curvature components must be positive while the other

is negative, meaning that the surface is curved in opposite directions. The area surrounding thepoint is concave in this case and resembles the shape of a saddle. Areas with negative Gaussiancurvature are colored blue.

• Zero Gaussian curvature. At least one of the two principal curvatures is zero, so the surface iseither completely flat or curved in only one direction. In both cases the surface is developable

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Illustration Illustration 5.15.1: Control point: Control pointform.form.

Illustration Illustration 5.25.2: Gaussian curvature display.: Gaussian curvature display.

DELFTship

(This is in fact a very important property of developable surfaces). These areas are colored green.• Positive Gaussian curvature. The curvature in both directions can be positive or negative, but

must have the same sign. These areas are convex and colored red.

● Zebra shading (Ctrl-E). Another option to check themodel for fairness. Regions with a constant light-reflection intensity are shaded in bands. This issimilar to the way the human eye detects unfair spotson a surface since the shininess and shadows vary inthose areas. If the edges of the zebra stripes arecurved smoothly then the surface is smooth in theseareas. At knuckle lines they vary abruptly.

5.6 5.6 Working with Working with background imagebackground imagessDELFTship has the ability to display images in the background of your model. This feature is particularlyconvenient if you have an existing linesplan on paper and want to recreate the lines in DELFTship. You can load amaximum of three images. Each ofthese images is assigned to a specificview (profile, plan or bodyplan view).You can not assign an image to theperspective view. All options related tobackground images are located in themenu that pops up if you press theright mouse button in a viewport. Whenusing background images you shouldpay special attention to make sure thatall horizontal and vertical lines on theimages are truly horizontal or vertical.

5.6.1 5.6.1 VisibleVisibleOnce you have assigned an image to for example the profile view, it will be shown in all viewports showing theprofile view on the model. By changing the visible property you can hide the image from a particular viewport.

5.6.2 5.6.2 ClearClearThe clear command removes the image not only from the current viewport but also from all other viewportsdisplaying the same view. It is entirely removed from the DELFTship model.

5.6.3 5.6.3 LoadLoadImports a background image. DELFTship only reads bmp and jpg images. For performance reasons you mustensure that the images you are going to use are not too big in size. After having imported an image you must setthe origin (paragraph 5.6.5 on page 16) to make sure it is displayed at the right location. You also have to set thescale of the image (paragraph 5.6.6 on page 16) to match the size and scale of your model. For importing severalimages, including their settings, the user is referred to paragraph 6.4 on page 23.

5.6.4 5.6.4 SaveSaveExports the background image as a bitmap image to a file.

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Illustration Illustration 5.35.3: Zebra stripe shading.: Zebra stripe shading.

Illustration Illustration 5.45.4: Using background images to trace an existing design.: Using background images to trace an existing design.

DELFTship

5.6.5 5.6.5 OriginOriginIf you use this option a special cursor is used to indicate you're modifying the origin of your background image.You can simply drag to image to the correct location by keeping the left button of your mouse pressed.

5.6.6 5.6.6 Set scaleSet scaleMake sure you set the scale of an imported image before opening another image. DELFTship assigns the samescale of the previously imported image to the freshly imported one. This is particularly useful if you have multipleimages imported from the same linesplan thus having the same scale. Whenever this option is executed the useris required to click on a point within the actual image of which the location is known. The program uses the samescale for both the horizontal and vertical direction.

5.6.7 5.6.7 Transparent colorTransparent colorQuite often background images are inblack and white. Having a huge whitearea on your viewport can sometimesbe distracting. By setting white as thetransparent color the program does notdraw the white areas. So only the blacklines are drawn on your screen. Thetransparent color is selected by clickingon an area of the background imagethat has the color you want to hide. Ifyou click on a point that lies outside thephysical area of the background imagetransparency is disabled again.Illustration 5.5 shows an example of atransparently rendered backgroundimage.

5.6.8 5.6.8 ToleranceToleranceSometimes images that simple seemjust black and white may have a lot ofshades of gray in between. This isparticularly the case where some of theimage quality has been lost due tocompression, as is the case with jpgimages. If white is the designatedtransparent color and is filtered out, alot of “nearly white” pixels remain ascan be seen on illustration 5.6. Byincreasing the filtering tolerance thesepixels can be excluded by the programtoo. Most of the time setting thetolerance to 30 is sufficient.

5.6.9 5.6.9 BlendingBlendingIf the background image is till too dominant it can be blended with the viewport color. By doing so it dissolves inthe background and the geometry of your DELFTship model will be better visible.

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Illustration Illustration 5.55.5: Background image made transparent.: Background image made transparent.

Illustration Illustration 5.65.6: Example where higher tolerance is needed.: Example where higher tolerance is needed.

DELFTship

6. 6. File import File import

6.1 6.1 Import surfaceImport surfaceThis feature is used to import a number of 3D curves from a textfile (make sure a decimal point is used for separating thedecimals, not a comma!). The program subsequently fits a loftedsurface through these curves. This is a good way to import roundbottomed hulls. The curves may have any number of points, andthe number of points might differ from curve to curve. Usually thecurves run from the bottom of the hull upwards, howeverlongitudinal curves are allowed too, just as long as all the curveshave the same orientation and run in the same direction. It isimportant that the curves do not overlap each other.

After opening the data file the user will be prompted to specify thenumber of points in longitudinal direction (number of columns)and in vertical direction (number of rows) the imported hull musthave. Then the program fits a B-Spline surface through thesepoints such that the new surface interpolates the original points.

The format used for the file is as follows:

● The first line of the file must either be a 0 (zero) or a 1. Azero indicates that all coordinates are in meters while aone indicates that the coordinates are in feet.

● Each curve is defined by a sequence of X,Y and Zcoordinates separated by at least 1 space.

● After the last coordinate of each curve there should be anempty line.

● The last line in the file should be 'EOF' in capitals.

The following is an brief example of a file containing 3 stations. Amore extensive sample file can be found in the subdirectory \shipsand is called Round hull import demo.txt. When importing such atext file DELFTship assumes the following:

● X-coordinates are longitudinal. Positive Y coordinatescorrespond with the port side of the ship. The base lies atz=0.0 and the aft perpendicular at x=0.0

● All curves have multiplicity of 1. Having 2 curves at thesame location leads to errors. Whenever 2 curves exist atthe same location, for example if the hull is fitted with abulbous bow, then these curves must be combined into asingle curve by connecting the segments with a line lying onthe center plane. These segments can later be removed.

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Illustration Illustration 6.16.1: Hull defined with transverse curves.: Hull defined with transverse curves.

Illustration Illustration 6.26.2: Hull defined by longitudinal curves.: Hull defined by longitudinal curves.

DELFTship

6.2 6.2 Import chinesImport chinesImporting a hard chined hull requires a slightly different approach as describedin the previous paragraph. Rather then creating a lofted surface ruled surfacesare fitted between two successive chines. The coordinates of each chine areread from an input file with the extension .txt. The input file has the same formatas described in paragraph 6.1 on page 17, except for the fact that the type ofcurves in the file is restricted to longitudinal curves only.

Once the data points of each chine have been read from file curves are fitted tothose points in such a way that the chines from the DELFTship hull match thesecurves. The number of control points is the same for each chine and can bespecified by the user. The original curves are also added to the model asmarkers as a reference. The file chines import demo.txt contains a moreelaborate demo. It is located in the DELFTship \ships subdirectory. The chinesmust be ordered from the bottom up with coordinates going from aft to front. Atleast three curves must be in the file representing:

1. The keel line2. At least one chine 3. The deck- or sheer line.

Control curves are added to the crease edges corresponding to each chine tomake it easier to fair the chines.

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DELFTship

6.3 6.3 Table of offsetsTable of offsets

The following is a description of the file format that is used for importing a table of offsets. The file should have .txtas a file extension and written as a proper ASCII text file. It looks like this:The first line contains the number of waterlines.The second line the number of stationsThe third line indicates whether data describing the deck line at each station is present (1) or not (0).The fourth line indicates whether data describing the contour line at each station is present (1) or not (0).The fifth line indicates whether data describing the aft contour at each waterline is present (1) or not (0).The sixth line indicates whether data describing the forward contour at each waterline is present (1) or not (0).The seventh line indicates whether data describing the flat of bottom at each station is present (1) or not (0).The next three lines describe the length, beam and draft of the ship as used in the project settings.

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Illustration Illustration 6.46.4: This line represents the heights of each of the 11 waterlines: This line represents the heights of each of the 11 waterlines

Illustration Illustration 6.36.3: Information stored in the file header: Information stored in the file header

DELFTship

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Illustration Illustration 6.66.6: Distance of each of the 20 stations ordered from aft to front.: Distance of each of the 20 stations ordered from aft to front.

Illustration Illustration 6.56.5: Distance of aft contour line to origin on each waterline.: Distance of aft contour line to origin on each waterline.

DELFTship

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Illustration Illustration 6.76.7: Distance of forward contour line to origin on each waterline.: Distance of forward contour line to origin on each waterline.

Illustration Illustration 6.86.8: Actual offsets data. The intersection of each column and row gives the half beam on that waterline and station. The bottom right: Actual offsets data. The intersection of each column and row gives the half beam on that waterline and station. The bottom rightvalue in the green rectangle indicates that on station 11.400 and waterline 1.600 the beam is 0.178.value in the green rectangle indicates that on station 11.400 and waterline 1.600 the beam is 0.178.

DELFTship

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Illustration Illustration 6.96.9: Data describing the deck line height (left column) and beam (right column) measured on each station.: Data describing the deck line height (left column) and beam (right column) measured on each station.

Illustration Illustration 6.106.10: The last column represents the height of the contour line on each station.: The last column represents the height of the contour line on each station.

DELFTship

6.4 6.4 Background imageBackground imagess..Use this option to import a file containing one or more background images that was exported from anotherDELFTship project. The file does not only contain the images but also all settings applied to these images such asscale origin, transparency etc. To import a single image for use in the current project see paragraph 5.6.3 on page15

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DELFTship

7. 7. Program preferencesProgram preferencesYou can modify the look and behavior of DELFTship bychanging the default settings in the preferences window.The actual appearance of this window might differ fromversion to version depending on which extensions areincluded into the software. The following settings can be modified:

7.1 7.1 GeneralGeneralModify the language used by the program. The languagefiles are located in the subdirectory delftship\languages ofthe program directory and only language files that arelocated in this specific directory can be selected. Aspecial piece of software is available fromwww.delftship.net that can be used to maintain existing orcreate new translations. Additionally the size of control points, amount of undomemory and color of the viewports can be altered.

7.2 7.2 HullformHullformChange settings of default colors used by the program fordisplaying various items.

7.3 7.3 HydrostaticsHydrostaticsSelect which hydrostatic properties should be displayed in the hydrostatics report or modify the order ofappearance by dragging the various properties in the list. All items will appear in the same order in the report asdisplayed in the list.

7.4 7.4 ReportReportModify the font type and size used in the reports throughout the program.

7.5 7.5 TankTankssModify color settings or the amount of transparency used for shading tanks. The transparency must be a value inthe range 0..255. A value of 0 means the tanks are completely solid (no transparency) whereas a value of 255means that they are fully transparent, even to the point where they are no longer visible.

7.6 7.6 Load caseLoad casessOn this page settings for the transparency of the hull surface and tanks used for drawing the load case in the loadcase editor window can be adjusted. The list to the right shows which items are included in the intact stabilityreport and in what order. The order can be modified by dragging items to a new positions. The check boxes can beused to exclude items from the report.

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Illustration Illustration 7.17.1: Tab pages from the preferences dialog.: Tab pages from the preferences dialog.

DELFTship

8. 8. Project settingsProject settingsIn the project settings window you can modify various project settings. It has a number of tab pages that variesdepending on the extensions included into the program.

8.1 8.1 GeneralGeneral

The first tab page is used for general information about theproject, such as:

● Project name● Name of the designer● Project comment● The name of the person who created the file● The type of units used for this project. This can either

be imperial or metric units.

When changing the unit format the entire model will bescaled to the new format. When switching from metersto feet for example all dimensions are divided by 0.3048.

● The shade underwater option is used to draw submerged surface areas in a alternate color when viewingthe shaded hull, linesplan, plate developments, inclined hydrostatics and load cases. Note: Only surfacesassigned to a layer that is included in the hydrostatics calculations is shaded this way.

● The save preview options is is used to store a small preview of the project in the file. This preview isprimarily used for browsing designs from the on-line design database on the DELFTship website.

● The simplify intersections option is more or less obsolete. When intersections such as stations arecalculated the can contain a large amount of points. This option removes points that do not substantiallycontribute to the shape of the calculated curves, however in some rare occasions it might lead toinaccurate curves. Only when file size is of importance it might be useful to use this option.

8.2 8.2 Main dimensionsMain dimensionsThe tab sheet to enter the main dimensions looks as shown onillustration 8.2. The project length generally is the lengthbetween perpendiculars for large ships or the waterline lengthfor pleasure craft.

The aft perpendicular is assumed to be located at x=0.0. Theforward perpendicular is located at the positive x-coordinatethat is equal to project length. (see also paragraph 4 on page10).

Depending on the hydrostatics settings these dimensions areused for calculating various hydrostatic coefficients such as the block coefficient. By default the midship locationlies at half the project length which is generally true for large ships. For some ships different values might bespecified.

The input values for the three draftmarks are optional and are only visible if the load cases extension is includedinto the software. The longitudinal location of the three marks can be specified together with the local keel platethickness. This information is used to calculate the actual draft measured from the keel under heel and trim forload cases.

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Illustration Illustration 8.18.1: General project settings.: General project settings.

Illustration Illustration 8.28.2: Main dimensions.: Main dimensions.

DELFTship

8.3 8.3 HydrostaticsHydrostaticsTab page to modify all hydrostatics related settings, such as the relative density of the surrounding water and theappendage coefficient . This is a factor normally used tocompensate for shell thickness and appendages such as therudder in the displacement calculation, usually in the range1.005 - 1.010. The professional edition also has an input valuefor the mean shellplate thickness. This is multiplied with thewetted surface area to obtain the submerged volume of theshell which is added to the displacement.

There's also a drop down box which can be used to specify howhydrostatic coefficients, such as the block coefficient andprismatic coefficient should be calculated. This can be doneusing either the dimensions specified in the project page(standard for large ships) or the actual dimensions of the submerged body (usually for yachts and small boats). Inthe latter case the submerged length and beam varies with the draft.

The program is not able to check whether the specified length and beam are correct. If one or more incorrectvalues have been specified the calculated coefficients mentioned above will also be incorrect!

Each time hydrostatic properties need to be calculated, the program checks if the direction of the normals of facesis consistent. It also automatically corrects the direction if necessary. In some rare cases it is possible that thenormals point in the wrong direction after this check. If this is the case erroneous hydrostatic values are the result,such as a negative volume and displacement. If this happens it is best to first disable the automatic surface checkand then manually correct the normals. When in doubt, always check the direction of normals manually byselecting control faces (paragraph 9.6.2 on page 33). Hydrostatic properties will not be calculated once leak pointsbecome submerged.

8.4 8.4 Critical pointCritical pointssThe critical points page is optional. Critical points are points that deserve special consideration for stabilitycalculations. DELFTship features the following types of critical points:

● Marker. These are points of which the userwants to know when they become submerged.Markers have no effect on a ship's stability.

● Downflooding. Probably the most importanttype of all. If a downflooding point issubmerged it means that the ship will floodand sink. Downflooding points are used toincorporate the location of openings in thehydrostatics calculations. These can bewindows, doors, hatches, ventilation openingsetc. Another option is to connect a tank to thesea water. If the point becomes submergedthe connected tank will be flooded. The actualflooding of the tank is NOT incorporated intothe hydrostatics or stability calculations however. To achieve this a tank has to be made non-buoyant (seeparagraph 13.2.1.7 on page 57).

● Weathertight. Openings that are weathertight are very important for damage stability calculations and aretreated in a special way. If a damage case has been solved and one or more weathertight openings aresubmerged in the equilibrium condition then the damage case is solved again but this time the connectedtanks will be flooded too. The process is repeated until the ship sinks or no other weathertight openingsbecome submerged in the equilibrium condition.

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Illustration Illustration 8.38.3: Hydrostatics settings.: Hydrostatics settings.

DELFTship

● Margin line. For use in the classical deterministic damage stability calculations.● Deck line. These points are used to check the amount of freeboard or when the deck edge becomes

submerged in the stability calculations which is used in several stability criteria. See paragraph 11.11 onpage 46 for a detailed description on the use of stability criteria.

● Tank connection. This type of critical point is used to connect two tanks for use in the (probabilistic)damage stability calculations. If the first tank is flooded and the water level rises above the location of thecritical point then the second tank will be flooded as well.

Critical points are primarily used in the extension for: cross curves, max VCG', the load cases and the probabilisticdamage stability. Each point needs a description to identify it and a location in 3D space. In addition you can usethe symmetry property if a critical point has a counterpart on the other side of the ship.

You can use the Windows Ctrl-C and Ctrl-V shortcuts to quickly copy properties of one critical point and apply it toanother.

8.5 8.5 TankTanks.s.On the tab page for tanks (optional) you can specify thepreferred use of tank names. If it is set to “abbreviation” thenthe tank abbreviation is used throughout the program, else thefull name of the tank will be displayed.

8.6 8.6 Load caseLoad casessThe load cases page is also optional. Several settings can bealtered. The most important of these are the heeling angles that are used to evaluate the stability while solving aload case. For very large ships it is often not necessary to go beyond 60°, while for sailing yachts heeling anglesup to 180° are not uncommon. Only positive values are allowedfor the heeling angles and the first angle must be zero. Themore heeling angles are calculated the more accurate thestability curve will be but how longer the entire calculationprocess will take.

The program is able to automatically determine which side theship heels to, but it is also possible to force it to calculatestability with a heel to either port or starboard.

Furthermore you can choose between a short version of theload case report or the default extensive version. Seeparagraph 14.2.6 on page 65 for more information about theload case report.

8.7 8.7 Longitudinal strengthLongitudinal strengthThe longitudinal strength tab page (optional). For complexvessels a huge number of weight items need to be evaluated inorder to calculate the shear force and bending moment. In thereport the results of the calculation are displayed on a regularinterval. A smaller interval yields more values. You can alsospecify the maximum values for the sagging and hoggingmoments.

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Illustration Illustration 8.48.4: Settings for tanks.: Settings for tanks.

Illustration Illustration 8.58.5: Load case settings.: Load case settings.

Illustration Illustration 8.68.6: Longitudinal strength.: Longitudinal strength.

DELFTship

8.8 8.8 Probabilistic damage stabilityProbabilistic damage stability..

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Illustration Illustration 8.78.7: Probabilistic damage stability: Probabilistic damage stability

DELFTship

9. 9. Edit optionsEdit options

9.1 9.1 UndoUndoThis feature can be used to undo previous editing actions. DELFTship stores all actions into memory. When a newfile is read into memory, the undo data associated with the previous model is cleared.

9.2 9.2 RedoRedoRedo a action that has been undone with the undo command.

9.3 9.3 DeleteDeleteUse this to delete items that have been selected. The program first deletes all selected faces, then the edges andfinally the selected points. Any points or edges that remain unused after this process are deleted also.

If a point is deleted all attached faces and edges are deleted too. If an edge is deleted, any attached faceswill also be deleted. See paragraph 9.4.3 on page 29 on how to remove a point without deleting theconnected faces and edges. Paragraph 9.5.3 on page 32 shows how to remove an edge without deleting theattached faces by using the edge collapse command.

Not only items from the surface geometry can be deleted this way but also markers, control curves, flowlines andtanks.

9.4 9.4 PointPoint

9.4.1 9.4.1 AddAddAdds a new point in 3D space. The new point is by default located at the origin (0.0, 0.0, 0.0). Adding new points is only enabled if the control net is visible.

9.4.2 9.4.2 AlignAlignIn the event that multiple points have been selected it is possible to align those points so that they form a straightline. This is done by projecting all the selected points on the line that goes through the first and last selected point.They are projected on the line rather than uniformly distributed to keep the displacement of the points minimal.Additionally you can also choose to only modify certain coordinates of the points. For example: if you haveselected multiple control points forming the outer edge of a transom you should only adjust the X-coordinate inorder to put all the points in the same plane seen from the profile view. The shape of the transom as seen from theback will in this particular case remain unaltered.

9.4.3 9.4.3 CollapseCollapseThis removes selected points without deleting the surrounding geometry. A point can only be collapsed if it isattached to exactly two edges. The point is then removed, and the two edges are replaced by a single edge. If apoint is attached to more than 2 edges, the other edges need to be removed first by collapsing these edges asexplained in paragraph 9.5.3 on page 32. The process of collapsing a point is shown on illustration 9.1. Note thatthe point that is to be collapsed is irregular since it has two faces connected to it and two edges. By collapsing thepoint the number of points of the two attached faces is reduced to 4 and the control net is made more regularmaking it easier to produce a fair hull surface.

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DELFTship

9.4.4 9.4.4 Fair pointsFair pointsYou can use the automatic fairing routine in DELFTship to fair the entire surface for you or only selected controlpoints. The automatic fairing routine will only affect internal points of the surface, points that are not located oncrease or boundary edges. These edges form feature lines on the hull that are generally very important for theappearance. Therefore it is best to fair those points manually or automatically by using control curves (paragraph9.7.2 on page 35). As the automatic fairing routine is called by the user the required points are shifted to a newlocation in such a manner that the overall smoothness of the surface improves. By repeatedly using the commanda very smooth surface can be obtained but the deviation of the original surface might be significant. If this methodof fairing is applied to models with just a few control points the faired surface might differ considerably from theoriginal surface. This is caused by the fact that the area of influence of a control point decreases with the totalnumber of points. The solution to this is to subdivide the control net to increase the number of points before usingthe automatic fairing algorithm. This process is described in paragraph 11.6 on page 44.

9.4.5 9.4.5 Plane intersectionPlane intersectionThe plane intersection algorithm intersects all visible edges with a plane. It inserts a new control point on eachedge that intersects that plane. Afterwards faces containing multiple newly inserted points will be split by insertinga new edge. This is a convenient way to insert for example a whole range of points at a certain ordinate location.There is also an option to add a control curve (paragraph 9.7.2 on page 35) to the newly created edges.The type of plane (vertical, horizontal or transverse) can be specified as well as the location by entering thedesired distance into the dialog.

9.4.6 9.4.6 Intersect layersIntersect layersYou can use this option to find the intersecting curve of two layers. Obviously this option is disabled in the menu inthe event that the model only has one layer. All the edges of the first layer are checked for an intersection with thefaces of the second layer. If an intersection exists than the the intersection point is inserted on the edge. Allinserted points are connected with new edges which form the intersecting curve of the two layers. Remember thatonly the first layer is affected by this entire operation, the second layer is left unmodified. Another thing to keep inmind is that points are only inserted in edges, not in faces. Intersecting layers is useful for example to find theintersection of the hull with a keel or rudder.

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Illustration Illustration 9.19.1: Removing a point with the collapsing command.: Removing a point with the collapsing command.

DELFTship

9.4.7 9.4.7 Copy valuesCopy valuesIf multiple control points have been selected you can copy values from the first selected point to all the otherpoints. This way you can quickly assign all selected points the same X, Y or Z coordinate.

9.4.8 9.4.8 Lock pointsLock pointsAll selected points will be locked. Locked points are shown as dark gray points on your screen and cannot bemodified. None of the available editing operations has any effect on locked points. This option will only be enabledin the menus if at least one unlocked point is selected.

9.4.9 9.4.9 UnUnlock pointslock pointsThis unlocks selected points that have previously been locked, so that they can be modified again. Again thisoption is only enabled in the menus if at least one locked point has been selected

9.4.10 9.4.10 UnlockUnlock all points all pointsAll locked points in the model will be unlocked, whether they are selected or not.

9.4.11 9.4.11 From From markermarkerssExtracts all points from the currently selected markers and adds these as control points to the subdivision surface.These control points are not connected by edges or faces yet.

9.5 9.5 EdgeEdge

9.5.1 9.5.1 ExtrudeExtrudeThe most used and preferred way to create new surfaces is byextruding edges. Since an edge may only have a maximum of twofaces attached, only boundary edges are allowed to be extruded.The selected edges are copied in the specified direction and newfaces are created between each old and new edge. The new facesare assigned to the active layer (see paragraph 9.8.1 on page 36)

Illustration 9.2 shows how a deck is easily added by extruding thesheerline. The three stages of the process are:

● Select the boundary edges that you want to extrude. Thenchoose the edit => edge => extrude option from themainmenu. A window will show up requesting direction ofthe extrusion. In the example the extrusion direction is(0.0, -2.25, 0.02) meaning that a copy of all selectededges will be created and moved 0.0 units in longitudinaldirection, -2.25 units in the transverse direction and 0.02units upwards.

● The extrusion command creates new faces between eachoriginal edge and its copy. These new faces will beassigned to the active layer.

● After moving the newly created edges to the centerline the deck is finished.

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Illustration Illustration 9.29.2: Create a deck by extruding edges.: Create a deck by extruding edges.

DELFTship

9.5.2 9.5.2 SplitSplitSelected edges are split by inserting a new point in the middle. After thisoperation all newly created points are selected. This is a convenient wayto insert new edges. In that case multiple edges can be selected and splitin two. All selected points belonging to the same face may then be split byinserting a new edge. The image to the right shows two selected edgesbefore and after the split. Note that this way a face consisting of 6 pointsis created, resulting in an irregular mesh (see paragraph 3.4 on page 9).The two selected points should preferably be connected, thus splitting theface in two regular faces. This ensures a more regular grid and asmoother surface.

9.5.3 9.5.3 CollapseCollapseCollapsing an edge removes the edge and combines the two attachedfaces into one new face. Since edge collapsing requires two faces it canonly be applied to internal edges and not to edges on the surfaceboundary.

9.5.4 9.5.4 InsertInsertA face can be divided by inserting an edge. To do this at least two pointshave to be selected. Both points must share the same face, and no edgeis allowed to already exist between the selected points. To ensure a fairsurface it is recommended to extend inserted edges as those seen onillustration 9.4 to a crease or boundary edge if possible.

9.5.5 9.5.5 CreaseCreaseSetting selected edges ascrease-edges allows theuser to add knuckle linesto the hull. The creaseproperty of boundaryedges cannot bechanged, they are bydefault treated as creaseedges. Illustration 9.5shows how a hard chineis created. To the left themodel without the chine isvisible. To the right theyacht with the newknuckle line is displayed.In this specific examplethe knuckle line runs overthe full length of the hull. This is not absolutely necessary, knuckle lines may run freely over the surface.

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Illustration Illustration 9.39.3: Inserting points on an edge.: Inserting points on an edge.

Illustration Illustration 9.49.4: Inserting an edge.: Inserting an edge.

Illustration Illustration 9.59.5: Creating knucklelines.: Creating knucklelines.

DELFTship

9.6 9.6 FaceFace

9.6.1 9.6.1 NewNewCreates a new face from selected points. These points have to be selected in the correct order.

9.6.2 9.6.2 InvertInvertThis option can be used to manually flip the direction of normals of selected faces to the other side in case theautomatic surface check has failed. All surface normals should point outwards, in the direction of the water. Thenormals of a face can be visualized by selecting the specific face. Make sure that both interior edges and normalsare made visible in your display settings (see chapter 10). Each displayed normal is calculated as the averagenormal in a point of the refined subdivision mesh. This average is calculated from all faces surrounding that point.Along the boundary of an edge sharing two faces with opposite normal directions, this may seem a bit peculiar ascan be seen on the left side of illustration 9.6. The normals along these boundaries look as if they are projected onthe surface. The right side of the illustration shows the normals after the face has been inverted and they normalsface the right direction.

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Illustration Illustration 9.69.6: Manually inverting the direction of face normals.: Manually inverting the direction of face normals.

DELFTship

9.7 9.7 CurveCurve

9.7.1 9.7.1 General information about General information about control curvecontrol curves and s and fairingfairing..To have a better control over the shape of the surface, control curves can be added to the model. These controlcurves are assigned to edges, and after each subdivision step the newly created edge-points are not only insertedinto the surface but also into the curve. This ensures that the control curves are always exactly embedded in thesurface. If the display of curvature plots is enabled from the display menu then selected control curves will bedrawn including their curvature plot. This curvature plot is updated in real-time if one of the control points of thecurve is moved making it an excellent fairing tool. If the curvature plot is interpreted and used correctly it ispossible to produce a perfectly fair surface provided the surface contains no irregular points (see paragraph 3.4 onpage 9). Bumps or dents in the surface that are normally too small to be seen on screen with the naked eye areeasily identified. Control curves are especially useful for fairing knuckle lines on the hull, such as the deck line,profile, and chines but they can also be used for fairing internal edges.

So what is curvature anyway? The curvature of a curve can be defined as follows:

the rate of change (at a point) of the angle between a curve and a tangent to the curve

In other words, the curvature is a measure for how strongly a curves changes in a point. It shipbuilding it isimportant that fair lines are produced where the curvature changes gradually along that curve.

Illustration 9.7 shows a controlcurve in the aft part of a containership. To the left the control curve isshown in blue, while to the right thecontrol curve is show in a selectedstate (yellow) together with it'scurvature plot (fuchsia). Thestraight parts of the curve have zerocurvature. If you travel along thecurve from the bottom to thedirection of the deck, first the curvestarts bending to the left. In thisarea the curvature is positive. At aheight of about 2.5 meters thecurve starts bending to the right,here curvature becomes negative.A little bit further along the curve itbends to the left again, so thecurvature becomes positive.

So how is this informationtranslated into the curvature plot?At regular intervals on the curve thecurvature is calculated and drawn as a line, perpendicular to the curve. The length of this line segment isproportional to the magnitude of the curvature in that point. If the curvature is negative the line is drawn on theopposite site of the curve. Whereas the absolute value of the curvature in a point is generally not that interesting,the way it changes along the curve is. This is a measure of the fairness of the curve. You don't want abruptchanges in the curvature plot, it should vary as smoothly as possible. And very often, especially with small boatsand yachts, a change of the sign of the curvature as seen in the image above is highly undesirable. Illustration 9.8shows an example of a control curve from a sailing yacht. The upper part of the image shows a poorly faired curve.

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Illustration Illustration 9.79.7: Control curve with curvature plot.: Control curve with curvature plot.

DELFTship

We see a change of the curvature sign in an area where it obviously should not occur, followed shortly after by asudden peak. The lower half of the image shows the same control curve after being faired using the automaticfairing tool for curves. The curvature nowchanges gradually and the curve is verysmooth.

One thing to bear in mind is that thecurvature at the first and the last point ofthe curve is always zero. The curve hasunclamped end conditions that correspondwith a natural wooden spline batten thathas no moment forced upon its ends. Thiscan be seen by the way the curvature plotcoincides with the end points of the curvebecause the curvature drops to zero.

Control curves are easier to fair if thepoints are spaced more or less evenlyalong the curve and are regular wheneverpossible. The less points a curve has, theeasier it is to produce a good runningsmooth curve.

9.7.2 9.7.2 NewNewTo add a new control curve first select a number of connected edges. (This is easier when you hold the control keyon your keyboard pressed down when selecting an edge with the mouse) Subsequently it is possible to create andassign a control curve to these edges. Only one curve can be assigned to each edge. If the new curve is notshown on the screen, make sure that control curves are made visible in your display settings.

9.7.3 9.7.3 FairFairThe automatic fairing routine for control curves can be used to quickly let the program fair the points for you. All thepoints defining the curve are distributed and moved in 3D to produce a better faired curve. The deckline fromillustration 9.9 was faired by using the command several times. Note that the curve has changed at the bow areaalso. To avoid this you can lock the points which you don't want to be affected by the fairing routine.

9.7.4 9.7.4 Convert to Convert to markermarkerThis option is only enabled if one or more control curves are selected. It converts the control curves into a markerfor future reference and to visualize or track changes made to the model. See also paragraph 11.8 for moreinformation on markers.

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Illustration Illustration 9.99.9: Deckline before and after applying the automatic fairing routine.: Deckline before and after applying the automatic fairing routine.

Illustration Illustration 9.89.8: Control curves of a sailing yacht.: Control curves of a sailing yacht.

DELFTship

9.8 9.8 LayerLayer

9.8.1 9.8.1 General layer informationGeneral layer information..The hull created with DELFTship consists of only 1 mathematical surface, even if the model contains multipleisolated layers or faces. When modeling it is often desirable to divide the model into different parts with differentproperties, such as for example the color. Therefore layers have been implemented into the program. A layer isnothing else than a container that groups faces together that share the same properties.

There must always be at least one layer in your model, and alsoone layer that is marked as active. Each time a new face is addedto the model it will be assigned to the active layer. You can identifywhich layer is active by looking at the layer toolbar at the top of thescreen (illustration 9.10) It contains a list of all layers, and only if nofaces are selected it displays the name of active layer. You canmodify which layer is active when no faces are selected by simplyselecting another layer from the drop down list in your toolbar.

If the event that faces have been selected there are twopossibilities:

● All selected faces belong to the same layer. In that casethe name of that layer is shown, even if it is not the active layer.

● The selected faces belong to different layers. No layer name is shown in the toolbar at all, it will be blank.

By selecting a layer from the list with layers while faces are selected, all the selected faces will be removed fromtheir current layer and assigned to this selected layer.

9.8.2 9.8.2 Active layer colorActive layer colorModify the color of the active layer. This color is also visible in the toolbar, right next to the drop-down listcontaining the layer names.

9.8.3 9.8.3 Auto groupAuto groupThis extracts groups of faces which are totally surrounded by crease edges. Then each group of faces is assignedto a new layer. If no faces are selected, every visible layer will be processed, otherwise only the selected faces.DELFTship tries to save as much of the present layer information as possible. If a set of faces is extracted, andthey already belong to the same layer then this layer is left undisturbed. Auto grouping is enabled in the menusonly if the display of interior edges is switched on.

9.8.4 9.8.4 NewNewAdd a new and empty layer to the model, and make it the active layer.

9.8.5 9.8.5 Delete emptyDelete emptyOnly enabled if the model contains at least two layers, one of which is empty. All empty layers are removed fromthe model. This also includes the active layer if it is empty. At least one layer will remain as the active layer, even ifthat layer is empty.

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Illustration Illustration 9.109.10: Layer toolbar showing the active layer.: Layer toolbar showing the active layer.

DELFTship

9.8.6 9.8.6 DialogDialogThis brings up the window whereyou can view and modify all thelayers. The following layerproperties can be modified:

● Description. The layername is displayed in theleftmost column.DELFTship does notrequire the layer name tobe a unique name, sinceall layers are identified by an internal unique identification number. Some CAD programs however, such asAutocad, do not allow spaces in the name of a layer or duplicate names. Exporting to such a program cancause problems if layers with identical names are used. It is therefore advisable to always use uniquedescriptions when naming layers.

● Visibile. These check boxes indicate whether the corresponding layer is visible or not. Click on the checkbox to turn the layer on or off. Points or edges from the control net belonging to invisible layers are alsohidden, which makes modeling of complex models easier.

● Symmetric. The free version of DELFTship does only support asymmetrical layers that do not contributethe hydrostatic calculations. In addition the professional version allows the use of asymmetrical layersprovided that those layers are completely (physically) separated from any symmetrical layers in yourmodel.

● Color. The layer color is used for drawing the model. It is also used in the linesplan and for platedevelopments. The color of a layer can be modified by clicking the small button displayed in the colorrectangle. A window is opened from which a new color can be chosen.

● Transparency. Sometimes it is nice to shade certain surfaces (partially) transparent, such as windows.The amount of transparency can be modified in the range from 0 (totally solid) to 255 (invisible). Note thattransparent shading might consume a lot of memory and significantly slow down the shading process.Since normal Z-buffer shading or plain alpha blending produces strange artifacts, the only way to do thisproperly is by keeping track of all surfaces covering a particular pixel on the screen and then drawing allthese surfaces from the back to the front. This process uses extra memory and CPU time, but apart frombeing a bit slower it should not pose any real problems.

● Hydrostatics. DELFTship uses the faces of the subdivision mesh for hydrostatic calculations (seeparagraph 15.3 on page 71) It calculates the volume enclosed by these faces. Sometimes however thesurface contains faces that should not be included in the hydrostatic calculations. This is particularly thecase if the faces of a layer do not form an enclosed volume, but only a bounded surface, such as a sail forexample. If a sail were to be included in the calculations, DELFTship would calculate the volume aft of thesail (if it is submerged) as a volume. Since this volume extends to infinity (there is no backside surfacepresent) it would introduce an error. So specific layers can be excluded from the calculations. See alsoparagraph 11.1 on page 43 for more information concerning leak points.

● Intersection curves. This property tells the program if a layer should be used when intersection curvesare calculated. For complex models it is often convenient to display stations, buttocks, waterlines anddiagonals of the hull only, and not for the deck, superstructure etc. This setting has no influence on thehydrostatics.

● Developable. Developable hulls are of particular interest to shipbuilders since they can be build from flatplates which are only bend in one direction. Most hulls are not developable since the surface is curved intwo directions (called compound curvature). Developable layers can be shaded differently. Developableareas of these layers are colored green while areas which are not developable are colored red. This is aconvenient way to visually check if a hull is indeed developable. Illustration 9.12 shows an example of adevelopable tug. It can immediately be seen by the green color that almost the entire hull is developable.Just a few very small spots in the topside and a larger area in front at the bottom are colored red. Thosevery small spots are mostly numeric errors (DELFTship uses a very small tolerance). The larger redbottom area however is not developable from a mathematical point of view. Developable hulls are oftenmade of plywood, which is far easier to bend than metal as a result of different material properties. In

37

Illustration Illustration 9.119.11: Layer properties.: Layer properties.

DELFTship

reality layers that are “almost” developable can perfectlybe build using plywood, whereas the same hull build ofmetal requires “torturing” the metal to get it into shape. Developable layers can be unfolded (or developed) by theprogram onto a flat plane for building purposes. This willbe explained in paragraph 15.8 on page 74.

● Loadcases. If this option is enabled the layer will bedrawn in the optional loadcases extension and theinclined hydrostatics extension. By excluding some layersyou can have a better view on the model. This setting willnot affect hydrostatic calculations.

● Linesplan. Sometimes a layer contains items you don'twant to be seen in the linesplan and it should beexcluded. Be aware though that the scale of items in thelinesplan is also determined by the intersection curves. Ifa layer would contain a sail, and the intersection curvesproperty is checked, intersection curves of this sail would still be calculated and seen in the linesplan, evenif the sail as a surface is not being drawn. Therefore it is best if you want to hide layers from this view toalso disable calculating intersection curves from those layers.

● Density. The relative density (compared to fresh water) of the material for a particular layer, for examply7.8 for steel.

● Thickness. The thickness of the surface. This value is only used for weight calculations, so stations forexample are not corrected for the shell thickness of the hull. By combining the surface area, thickness anddensity the approximate weight can be calculated. This weight is displayed in the design hydrostaticsreport (paragraph 15.3 on page 71) together with the center of gravity for each layer.

The black up and down arrows in the tool bar can be used to move a selected layer up or down in the list.Developable layers will appear in the same order in the window with developed panels as displayed in this list.

In the layer dialog you can use Ctrl-C to copy all the properties of the selected layer. By pressing Ctrl-V theseproperties can be quickly pasted to another layer.

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Illustration Illustration 9.129.12: Developable areas.: Developable areas.

DELFTship

10. 10. DisplayDisplayThis chapter deals with the various display settings that are available inDELFTship. Please not that some of the settings are optional, dependingon the purchased extensions.

10.1 10.1 ControlnetControlnetThe controlnet is the combination of all points and edges that form theinitial subdivision mesh. These are the entities that can be manipulatedby the user to shape the surface. If all the faces attached to a certainpoint or edge belong to layers which are turned off, it will not be drawn onthe screen. That way only the points or edges of interest will be shown.

10.2 10.2 Control curveControl curvessControl curves are curves that are assigned to edges of the controlnet and are used to fair the surface (seeparagraph 9.7.1 on page 34). The visibility of these control curves is not depending on the visibility of thecontrolnet. In fact, selecting and manipulating control curves is often easier if the control net is not visible. Pointsand edges assigned to a control curve automatically become visible whenever a control curve is selected, all otherpoints will remain hidden.

10.3 10.3 Interior edgesInterior edgesThe interior edges are in fact the edges of the subdivided surface. Thehigher the precision is set, the more edges are shown. The interior edgesare drawn in the color of the layer they are assigned to. You can select aface by clicking on one of the interior edges of that face.

10.4 10.4 Show both sidesShow both sidesSince most surfaces are symmetrical with respect to the center plane, onlythe portside of the hull is modeled and symmetrical surfaces are virtuallymirrored by the software to reduce the modeling time. If less information isshown it is easier to select a point, edge or face. Both sides can be shownhowever so that the designer has a good impression of what the entiremodel looks like. Not only the surface is drawn symmetrical, also theintersection curves, flowlines, control curves etc. Showing both sides of thehull is possible in both wireframe view and shaded views.

10.5 10.5 GridGridIf intersection curves are added to the model it is possible to have a griddisplayed that marks the location of these intersection curves. It is visible in wireframe and shaded mode and nextto each line its distance to the origin is printed. In addition the baseline, centerline and design waterline are alsoindicated. The grid is visible in all views except for the perspective view. It is displayed regardless of the displaysettings of the intersection curves. The same grid is also visible in the linesplan. See illustration 10.4 for anexample.

39

Illustration Illustration 10.110.1: Controlnet: Controlnet

Illustration Illustration 10.210.2: Interior edges.: Interior edges.

Illustration Illustration 10.310.3: Show both sides of the: Show both sides of themodel.model.

DELFTship

10.6 10.6 StationsStationsUse this setting to modify the display of stations. If no stations have been added to the model the option will bedisabled in the menus.

10.7 10.7 ButtocksButtocksUse this setting to modify the display of buttocks. If no buttocks have been added to the model the option will bedisabled.

10.8 10.8 WaterlinesWaterlinesUse this setting to modify the display of waterlines. If no waterlines have been added to the model the option willbe disabled in the menus.

10.9 10.9 DiagonalsDiagonalsUse this setting to modify the display of diagonals. If no diagonals have been added to the model the option will bedisabled.

10.10 10.10 Hydrostatic featuresHydrostatic featuresDELFTship also provides the option to plot some key hydrostatic values in the model for the design draft. These are:

● Displacement and center of buoyancy● Center of flotation● Lateral area and center of effort● Transverse metacentric height● Curve of sectional areas. Contrary to the other values

this curve is only plotted in the profile view of the hull.

Of course these values can only be displayed if the model isconsistent enough to calculate the hydrostatics, meaning thatif the model contains leak points below the water plane no values will be calculated or displayed. The values areupdated in real-time when the model is being modified. You can specify which data you want the program to showin the project settings window (see paragraph 8.3 on page 26)

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Illustration Illustration 10.410.4: Grid of stations, buttocks and waterlines.: Grid of stations, buttocks and waterlines.

Illustration Illustration 10.510.5: Hydrostatic features.: Hydrostatic features.

DELFTship

10.11 10.11 Critical pointCritical pointssCritical points can also be displayed in all views. See paragraph 8.4 on page 26 for more information regardingcritical points. The display option for critical points is optional for the professional version of the software.

10.12 10.12 Leak pointLeak points onlys onlyBy enabling this display option all regular control points will behidden from the control net so only points from the model that areconsidered “leak” by the program will be drawn. This makes iteasier to identify points restraining the hydrostatic calculations.Paragraph 11.1 on page 43 covers leak points in detail.

10.13 10.13 FlowlineFlowlinessThe flowlines that are displayed by DELFTship are calculatedthrough analysis of the surface geometry only and have nothing to do with CFD. This is a huge simplification sincespeed, pressure and waves are excluded from the calculation. Despite this simplification the flowlines show aremarkable resemblance with those calculated with CFDprograms at low speeds, but they only are meant to give thedesigner an impression of how the water will approximately flow.Real CFD calculations are of course much more accurate andreliable.

Flowlines are added by keeping the alt-button pressed andclicking with the mouse on a point below the waterline (profile,plan or body plan view only). This point is used as the origin ofthe flowline. From there the flow is traced as far as possible tothe stern until it penetrates the design waterline.

Flowlines are only traced along surfaces that belong to a layer that is also used for hydrostatic calculations(generally the shell of the hull). The image above shows some flowlines at the bow of a hull with a bulb fitted. Thebackground image shows the results obtained from a CFD calculation. The small black lines represent thedirection of the flow as calculated with CFD, the blue curves are the flowlines calculated by DELFTship. Flowlinescan be selected and deleted like any other geometry.

Areas on the surface where flowlines are converging to each other are high pressure areas whilst areaswhere the flowlines diverge are low-pressure areas.

10.14 10.14 NormalsNormalsIf this option is switched on, normals of faces that have been selected are displayed. These normals are drawn asthin white lines, pointing either inward or outward the hull (illustration 9.6). This display option is disabled if thedisplay of interior is set to false (paragraph 10.3 on page 39). A normal is drawn at each interior point of thesubdivision surface. The higher the precision is set, the more normals are drawn.

10.15 10.15 CurvatureCurvatureThis option enables or disables the drawing of the curvature plot of control curves and certain intersection curves.Only of intersection curves which appear checked in the intersection dialog (paragraph 15.1 on page 70) thecurvature will be plotted.

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Illustration Illustration 10.710.7: Flowlines.: Flowlines.

Illustration Illustration 10.610.6: Only the leak points of the model are: Only the leak points of the model aredisplayed.displayed.

DELFTship

10.16 10.16 MarkerMarkerssMarkers are curves that are added to the model as a reference. For example the body plan of an existing designcould be imported as markers. Stations could then be added to the DELFTship model at the same location as themarkers. Finally the points can be dragged until the stations and the markers are exactly on top of each other. Inthat case the DELFTship hull matches the hull from the existing design. For more information on markers pleaseread paragraph 11.8 on page 44.

10.17 10.17 MarkerMarker points. points.Sometimes markers contain so many points that displaying these points obscures the marker or even the model.In other cases you're only interested in the shape of the markers, not the points used to model the markers. To thatpurpose the marker points can be hidden from view. Note that this option is only enabled in the menus if thedisplay of markers is set to true. (see also the previous paragraph).

10.18 10.18 TankTankssEnables/disables the drawing of tanks. If the model contains tanks and a number of modifications to the hull haveto be performed it is better to turn of the displaying of tanks. Otherwise all tanks have to be rebuild after each hullmodification which can be time consuming.

10.19 10.19 Sounding pipesSounding pipesDisplay sounding pipes of tanks (only enabled if the model contains tanks and the display of tanks is set to true).

10.20 10.20 Transparent Transparent tanktankssSwitch between solid shading of tanks or transparent shading.

10.21 10.21 TankTank names namesDisplay the names of tanks in the model.

10.22 10.22 CurvatureCurvature scale scaleThe scale of the curvature plot of control curves and intersection curves can be decreased by pressing the F9 key,so that curves with high curvature can be evaluated. Pressing F10 increases the curvature scale.

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DELFTship

11. 11. ToolsTools

11.1 11.1 Check modelCheck modelDELFTship can check the model for any inconsistencies, and corrects most of them automatically. This check isalso performed each time hydrostatics are calculated, unless automatic checking is disabled in the project settings(paragraph 8.3 page 26) . First of all the surface is checked for any disjoint segments. Then each segment ischecked for a consistent direction of the face normals. If not, it adapts those faces. Next the lowest point of eachisolated surface segment is identified. For conventional ships this usually is the bottom. If this is indeed a point onthe bottom then the average normal of this point should point down in order to face the water. Under thisassumption all faces are adapted such that the direction of their normal corresponds to the direction of the normalof this particular point. In some rare cases this might cause the normals to point in the wrong direction. In that caseit is recommended to manually flip the normals to the correct side (see paragraph 9.6.2 on page 33) and to disableautomatic checking of the surface. This test also identifies edges with more than two faces attached. Secondly alist of leak points is provided where the hull is considered leak. A point is considered “leak” if:

● It is not situated on the center plane, meaning that the y-coordinate of the point >0.0001.● The point is situated on a boundary edge (An edge with only 1 face attached to it).

Note that for hydrostatic calculations an edge counts also as a boundary edge if two faces areattached to it of which one is excluded from hydrostatic calculations. This could for example be thecase for a ship with a closed deck, from which the deck is put in a separate layer that is not includedin the hydrostatics calculations. In that case DELFTship keeps calculating until the deck line issubmerged. Also windows or any other none watertight surfaces could be treated similar.

It is important to realize that leak points are not actually always leak in the sense that they are always makingwater. A leak point in DELFTship is a point that is potentially leak and only becomes actually leak if it issubmerged. So the presence of leak points does not always have to pose a problem, just as long as they arenot submerged.

If more then 10 leak points are found, only the first 10 are displayed. The points are shown sorted in increasingheight above the base plane.

Finally, if the test is called from the menu, an overview of corrected items and possible remaining errors is shown.

11.2 11.2 Move to baselineMove to baselineIn DELFTship the draft is always measured from the baseline. If the lower point of the hull does not coincide withZ=0.0 the model can simply be moved to the correct vertical position with this command. The lowest point of alllayers that are included in the hydrostatics is calculated and the model is moved vertically such that this lowestpoint will be on the baseline. Note that after this operation it is still possible that surfaces not included in thehydrostatic calculation are located below the baseline.

11.3 11.3 Remove negativeRemove negativeSometimes, after importing a hull the geometry of both sides of the ship is present. DELFTship only needs the portside. This option removes all faces from the model that are completely on the starboard side.

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DELFTship

11.4 11.4 Remove unused pointsRemove unused pointsRemove all points from the model that have no edge or faces connected to it.

11.5 11.5 Extract Extract critical pointcritical pointssExtract control points from a selected set of control points and control edges. Rather than the position of thecontrol points the corresponding points on the surface are added to the list with critical points. A dialog is shownwhere the user can specify the type and symmetry of the critical points he wants to add.Note: This option is only visible in the menus if the critical points extension is included.

11.6 11.6 Subdivide Subdivide controlnetcontrolnetIf a model contains too few control points you can subdivide thecontrolnet to increase the number of points so more detailedmodeling can be performed. This is a global action however, so itincreases the number of points throughout the entire model. Thisoption can be particularly useful in combination with the automaticfairing routine described in paragraph 9.4.4 on page 30.

11.7 11.7 Keel and rudder wizardKeel and rudder wizardThe keel and rudder wizard enables the user to quickly define akeel or rudder with a predefined planform. You can select thedesired wing section from a list of standard NACA sections. Thekeel or rudder is show in 3D along with it basic properties such asaspect ratio, volume, center of buoyancy etc. Once the keel orrudder is complete it can be exported in two ways. Using the “send”button it is inserted at the current DELFTship model at the origin.Using the “save as part” button it can be saved to a file as aDELFTship part which can be imported in other designs. Thelift/drag tab shows an estimation for the lift and drag curves.

11.8 11.8 MarkerMarkerssMarkers are curves that can be added to the model as a reference. For example the offsets of another design canbe imported as markers. Then intersection curves can be specified at the same location as the offset data inDELFTship. If the intersection curves coincide with the markers both models are exactly the same. Another use formarkers is to visually check the differences between two versions of a design. If you convert all stations to markersbefore modifying the model then the difference between the markers and updated stations reflect the modificationsmade to the design.

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Illustration Illustration 11.211.2: Keel and rudder wizard.: Keel and rudder wizard.

Illustration Illustration 11.111.1: Control net before and after subdividing.: Control net before and after subdividing.

DELFTship

11.8.1 11.8.1 ImportImportDELFTship can read the following file formats and convert the datainto markers:

● Autocad DXF files (*.dxf). The files need to be in AutocadR12 format. Only lines, polylines arcs and circles areimported as markers.

● IGES files (*.igs, *.iges). The following entities areimported as markers:

● NURB curves (entity 126)● DELFTship marker files (*.mrk). This native file format is

meant to exchange markers between different (versions of)designs.

● Text files (*.txt). If you need a different way to importmarkers you can specify the data yourself in a text file. Thefile should meet the following format:

• The first line of the file must either be a 0 (zero) or a1. A zero indicates that all coordinates are in meterswhile a one indicates that the coordinates are infeet.

• Each curve is defined by a sequence of X,Y and Zcoordinates separated by at least 1 space.

• You can optionally add the word “KNUCKLE” afterthe z coordinate to introduce a knuckle point in thecurve.

• The end of a curve is indicated by an empty lineafter the last coordinate.

• The last line in the file should be 'EOF' (usecapitals). The following is an example of a file containing 3 longitudinal curves.

11.8.2 11.8.2 ExportExportAll available marker curves are exported to a file in the native file format of DELFTship. This file has theextension .mrk and can be imported into other designs.

11.8.3 11.8.3 DeleteDeleteThis deletes all markers from the model. It speaks for itself that this option is disabled if there are no markersadded to the model.

11.9 11.9 Add Add boxboxUse this option to add a box shaped volume to your model, for example to represent a superstructure or even as astarting point for a new hull. The box can be added to either the currently active layer or to a new layer.

11.10 11.10 Add Add cylindercylinderLets you add a cylinder to the model. You can specify the start point, endpoint, radius and number of points in thewindow that appears. The points are calculated in such a way that the resulting surface has the requiredproperties, even though the points are located outside the cylinder. The minimum number of points that can beused to form the cylindrical shape is 4, however 6 or more is recommended. You can use the cylinder for exampleto add a bow thruster to your model. Optionally the cylinder can be added to the currently active layer or to a newlayer.

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1 0.000 0.000 0.150 0.856 0.000 0.048 1.884 0.000 -0.046 3.939 0.000 -0.158 KNUCKLE 4.966 0.000 -0.184 5.994 0.000 -0.195 8.049 0.000 -0.192 9.590 0.000 -0.163 10.618 0.000 -0.122 11.645 0.000 -0.059 13.700 0.000 0.150 -0.771 0.000 1.056 0.685 0.662 0.844 2.398 1.219 0.666 4.110 1.536 0.565 5.822 1.664 0.524 7.535 1.672 0.522 9.248 1.575 0.553 10.960 1.300 0.640 KNUCKLE 12.672 0.795 0.802 14.471 0.000 1.056

-0.053 0.000 1.683 0.856 0.421 1.498 2.911 1.071 1.211 4.966 1.375 1.077 7.021 1.436 1.050 9.076 1.344 1.090 11.131 0.989 1.247 13.186 0.272 1.563 13.753 0.000 1.683

EOF

DELFTship

11.11 11.11 Edit criteriaEdit criteriaThe professional version of DELFTship includes a list with default stability criteria. Those criteria are programmedin such a way that it's relatively easy for the user to create his own set if for some reason the included criteria arenot sufficient or applicable. A set of stability criteria must always be selected in order to calculate load cases or toperform the max vcg' calculations. There are two different ways to open the window with stability criteria:

1. Through the load case tab from the project settings window (see paragraph 8.6 on page 27). This iscorrect way if you want to select a set of criteria for your project or if you want to modify settings of thealready selected project criteria. The selected criteria for your project will be stored in the project file.Modifications the the criteria other than the project criteria are not saved to file and will be lost.

2. By using the “Edit criteria” option from the main menu. This allows you to modify (and save) the list withcriteria for future use. No modifications are made to the the selected set of criteria from your currentlyopen project since those criteria are stored in the project file rather than the criteria list.

Illustration 11.3 shows the stability criteriawindow. The criteria tree to the left of thewindow allows you to group criteriatogether any way you like using so called“sections”. By selecting a criterion or a setof criteria it will become active and itsproperties are displayed to the right. Allcriteria or sections can have a lockdisplayed next to them in the tree.Depending on the color of this lock it hasthe following meaning:

● Yellow: The selected item or itschildren are not locked in any wayand can be freely modified.Possible input fields in the grid tothe right are displayed in white.

● Gray: The selected set or criterionis locked. It can still be modifiedby the user after unlocking it.Locking or unlocking is simply done by clicking on the lock with the left mouse button. You can lock orunlock a individual criterion, but if you lock the parent section of a criterion than all underlying items willalso be locked. All input fields will be displayed in gray to indicate they can not be modified. You can notunlock an item if its parent is still locked without unlocking this parent first.

● Blue: These are special items that are frozen. These items can not be unfrozen, unlocked or modified inany way, not even deleted. However it is possible to create a copy of those items which can be unlockedand modified.

Besides the lock an additional image is drawn in some cases:● Each criterion has a light bulb displayed next to it. If the light bulb is yellow the criterion will be drawn in the

stability curve. If it is white then the criterion will not be visible in the graph of the stability curve. Note thatthis setting only affects the appearance of the stability curve, it does not exclude a criterion from the testthat checks whether a set of criteria complies or not.

● A section can have only the lock displayed or another additional image that resembles a stability curve. Inthe first case the section contains other sections or is empty. In the second case the image indicates thatthe section is in fact a valid set of criteria that can be selected for a project. If the image with the stabilitycurve is not displayed then the section can not be selected as project criteria!

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Illustration Illustration 11.311.3: Stability criteria window.: Stability criteria window.

DELFTship

DELFTship distinguishes the following objects that can be used in the process of making your own set of stabilitycriteria:

11.11.1 11.11.1 SectionSectionA section is a container for other sections or criteria. If asection contains other sections it is no longer considered aselectable set of criteria any more.The parameters of a section that can be modified are:

● Description. The description should be chosencarefully as it is displayed in the reports of load caseand max vcg' calculations. The description can bemodified by modifying the description text in thecriteria tree.

● Valid for. This additional line of text is displayed alsoin the reports and should indicate to what type ofvessels the criteria are applicable.

● Desired units for output. This input field makes itpossible to switch between the type of units used forinput and output of values for the underlying criteria. Ifthe selected section does not represent a selectable set than this parameter remains hidden.

11.11.2 11.11.2 FreeboardFreeboardThe freeboard criterion is used to check if a minimum amountof freeboard is achieved. In order to be able to check thefreeboard a sufficient number of critical points of the deck linetype must be specified. The calculated freeboard is thesmallest distance of any of the deck line points to the waterplane. The following parameters may be specified:

● Required value. The minimum required value for thefreeboard.

11.11.3 11.11.3 Equilibrium angle.Equilibrium angle.This criterion is used to check if the equilibrium angle does notexceed a specified value.The following parameters may be specified:

● Required value. The maximum allowed heeling anglefor the equilibrium state.

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Illustration Illustration 11.411.4: Parameters for a section.: Parameters for a section.

Illustration Illustration 11.511.5: Freeboard criterion.: Freeboard criterion.

Illustration Illustration 11.611.6: Equilibrium angle.: Equilibrium angle.

DELFTship

11.11.4 11.11.4 Combined heel and trim angle.Combined heel and trim angle.For small barges containing lifting equipment a requirementcan be that the combined angles for heel and trim are notallowed to exceed a certain value. The following parametersmay be specified:

● Required value. The maximum allowed value for thesum of the heeling and trim angles in the equilibriumstate.

11.11.5 11.11.5 Area under the GZ curveArea under the GZ curveThis is a very frequently used criterion which calculates thearea under the GZ curve between two heeling angles.The following parameters may be specified:

● The lower angle. This can either be a user definedangle, the equilibrium angle or both. In case both areto used the greater of the two angles is chosen.

● The upper angle can be a combination of a userdefined angle, the downflooding angle (if criticalpoints have been specified), the angle of vanishingstability and the angle at which the maximum GZoccurs. If more than one angle is selected then thelowest value is used for the upper angle.

● Required area varies with angle of max GZ. Most ofthe times the required area is a constant value. Sometimes however the required area depends on theangle of maximum GZ. In that case 4 values must bespecified:

● A lower limit heeling angle● The corresponding required area at this angle● An upper limit heeling angle● The corresponding required area at this angle

If the angle of max. GZ is smaller than the lower limitangle the lower limit area is used (yellow area fromillustration 11.9). If the angle of max. GZ is largerthan the upper limit angle then the required areacorresponding to the upper limit is used (green area).In case the angle at which max. GZ occurs is inbetween the two defined limits then the required areais obtained by linear interpolating between the twodefined required areas (gray area).

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Illustration Illustration 11.811.8: Area under the GZ curve criterion.: Area under the GZ curve criterion.

Illustration Illustration 11.911.9: Required area under the GZ curve varies.: Required area under the GZ curve varies.

Illustration Illustration 11.711.7: Combined heel and trim angle.: Combined heel and trim angle.

DELFTship

11.11.6 11.11.6 Value of max. GZValue of max. GZThis criterion calculates the maximum value of the GZ curvebetween two limiting angles.

● The lower limit can be a user defined angle, theequilibrium angle or the greater of both.

● The upper limit is a heeling angle defined by the user,the downflooding angle, the angle corresponding tothe first peak in the GZ curve or the smallest value ofthose angles in case a combination of multiple valuesis used.

● Heeling moment. In addition you can select a heelingmoment criterion if the set contains such a criterion.In that case the GZ is corrected by subtracting theheeling arm and the remaining value is used to test ifthis criterion complies.

● The final parameter is the required value for thecriterion that must be met. Normally this is a constantvalue. According to some regulations however therequired minimum value for GZ depends on the angle of vanishing stability according to the followingformula: GZRequired = C1-C2*ϕV where:

C1 = a constant.C2 = a multiplier for the angle of vanishing stability. When set to zero the required value will beequal to C1.ΦV = the angle of vanishing stability (in radians).

Additionally you can specify the lower and upper limit tobe used for the angle of vanishing stability.

11.11.7 11.11.7 Angle of max. GZAngle of max. GZBesides the maximum value of the GZ curve also the heelingangle at which this maximum value occurs is an importantcriterion. By default the full range of the curve is evaluatedhowever by modifying the following settings you can limit thisrange:

● First peak in the GZ curve. The part after the fist peakis ignored even if the GZ curve rises again after thisfirst peak.

● Downflooding value. The curve is evaluated up to thedownflooding angle.

● The lesser angle of the two is used if both areparameters are chosen.

11.11.8 11.11.8 Metacentric heightMetacentric heightThis is a relatively simple criterion with only a few parameters:

● User defined heeling angle. If this option is enabledthen the GM is calculated for the user defined heelingangle. If disabled the equilibrium angle is being used.

● Heeling angle. The user defined heeling angledescribed above.

● Required value. The value of GM that must be met.

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Illustration Illustration 11.1111.11: Input parameters for the "Angle of max. GZ": Input parameters for the "Angle of max. GZ"criterioncriterion

Illustration Illustration 11.1211.12: Input parameters for the "Metacentric: Input parameters for the "Metacentricheight"criterionheight"criterion

Illustration Illustration 11.1011.10: Input parameters for the “Value of max. GZ”: Input parameters for the “Value of max. GZ”criterion.criterion.

DELFTship

11.11.9 11.11.9 GM in damaged condition.GM in damaged condition.This criterion is used to use the GM values from the damagestability calculations as an extra constraint for the minimumrequired GM values. The following parameters can bespecified:

● Partial draft. The partial draft according to theregulations for (probabilistic) damage stability.

● Minimum GM'. The Minimum required value for GMfor the partial draft.

● Summer draft. The summer draft.● Minimum GM'. The Minimum required value for GM

for the summer draft.

11.11.10 11.11.10 Wind heeling criterionWind heeling criterionThe wind heeling criterion is a complicated criterion with a lotof parameters. This criterion is always used in combinationwith a wind silhouette. If no silhouette is selected in the loadcase or max VCG' calculations then the criterion will not bemet. Summarized the criterion calculates the heeling anglecaused by a static wind pressure. Then it is assumed the hullrolls back to a certain angle due to the action of waves. Finallya wind gust is applied to the ship and the area between thewind gust heeling arm and the GZ curve is calculated. Thearea left of the wind gust equilibrium angle (14.2o onillustration 13.5) is called “Area A” while the area to the right iscalled “Area B”. The settings that can be adjusted for this criterion are:

● Wind speed. Wind speed in knots.● Drag coefficient CD. The default value for CD according

to the IMO is 1.220. The formula to calculate thewindpressure on the silhouette is 0.5*g*ρ*CD*V2

where:g is the gravitational accelerationρ is the density of air.CD is the drag coefficient of the projected silhouette.V is the windspeed in m/sec.

● Cosinus power. The formula used to calculate the wind heeling moment for any given heeling angle is:Mφ=M0*cos(φ)N where:

Mφ is the wind heeling moment at heeling angle φM0 is the wind moment in upright position.N is the value for “cosinus power”. A value of 0 will result in a constant heeling moment for allheeling angles as prescribed by the IMO. By setting this value to 1 the wind lever will be multipliedwith cos( φ)1. If set to 2 the lever will be multiplied with cos( φ)2.

● Wind gust multiplier. A factor to calculate the wind pressure of the wind gust relative to the static windpressure. The IMO prescribes 1.5 times the static wind pressure.

● Lateral CE at half draft. By default DELFTship calculates the heeling lever as the vertical height betweenthe center of effort of the wind area and the lateral center of effort. The latter is calculated exactly from thewind silhouette. If this option is enabled the actual height of the lateral center of effort is replaced by theships half draft which is in most cases slightly lower.

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Illustration Illustration 11.1311.13: GM in damaged condition.: GM in damaged condition.

Illustration Illustration 11.1411.14: Input parameters for the wind heeling criterion.: Input parameters for the wind heeling criterion.

DELFTship

● Area B is calculated from the wind gust equilibrium angle to an upper angle which can be a user definedangle, the downflooding angle, the angle of the first peak in the GZ curve, the angle at which the maximumGZ occurs or a combination. If multiple limits for the upper angle are specified then the lesser value will beused.

● Use IMO rollback angle. The IMO offers aformula that can be used to calculate therollback angle due to the action of waves. Theformula uses information automaticallyextracted from the hull, such as LWL and CB forexample, but also the type of bilge and thebilgekeel area which are stored in the windsilhouette (see also paragraph 14.3 on page68). If this option is selected the IMO formula forthe rollback angle is used, otherwise the usermust manually specify a rollback angle.

● Test for maximum static heeling angle. Thisoption should be enabled if the heeling anglecaused by the static wind pressure is notallowed to exceed a certain maximum angle.

● Maximum allowed static heeling angle. Theactual value of the maximum allowed heelingangle due to static wind.

● Test static angle against against deck immersion angle. This parameter limits the heeling angle as apercentage of the deck immersion angle. The IMO uses a maximum allowable heeling angle of 80% of thedeck immersion angle for example.

● Max. allowed ratio static angle/deck immersion angle. Used in combination with the previous parameter.This is the actual allowed ratio expressed as the maximum allowed heeling angle divided by the deckimmersion angle. The value must be in the range 0.0 -1.0 and is 0.80 for the IMO wind criterion.

● Ratio of AreaA/AreaB. Used in combination with the next parameter.● Required ratio of areas. The area ratio is a dimensionless number calculated as Area A/Area B. As long as

the value for Area B is larger than the value calculated for Area A the ship has enough stability to recoverfrom the wind gust. If it is smaller than it will capsize.

11.11.11 11.11.11 Passenger crowding anglePassenger crowding angleCriterion for passenger vessels that tests whether the heelingangle caused by putting all passengers a certain distancefrom the centerline of the vessel does not exceed a maximumheeling angle. The magnitude of the exerted heeling momentdepends on:

● The number of passengers the vessel was designedfor.

● Passenger weight. Average weight for eachpassenger.

● Passenger location. You can choose between half thebeam of the ship (as specified in the project settings)or a user defined distance.

● Cosinus power. The formula used to calculate theheeling moment for any given heeling angle isMφ=M0*cos(φ)N where

Mφ is the heeling moment at heeling angle φM0 is the upright heeling moment.N is the value for “cosinus power”. A value of 0 will result in a constant heeling moment for allheeling angles.

● Required value. The maximum heeling angle that is allowed.

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Illustration Illustration 11.1611.16: Input parameters for the "Passenger crowding": Input parameters for the "Passenger crowding"criterion.criterion.

Illustration Illustration 11.1511.15: Wind heeling criterion AreaA and AreaB: Wind heeling criterion AreaA and AreaB

DELFTship

11.11.12 11.11.12 High speed turning angleHigh speed turning angle

The heeling angle caused by turning the ship at high speed isalso limited in some cases. The heeling moment is calculatedfrom:

● Service speed. The speed of the ship while turning.This speed is in knots.

● Turning radius. The turning radius can be specified asan absolute value or expressed in terms of the shipslength.

● The heeling lever. This can either be the height ofVCG above half the draft or a user specified value.

● A constant multiplier is used to increase or decreasethe heeling moment.

● Cosinus power. The formula used to calculate theheeling moment for any given heeling angle isMφ=M0*cos(φ)N where

Mφ is the heeling moment at heeling angle φM0 is the upright heeling moment.N is the value for “cosinus power”. A value of 0 will result in a constant heeling moment for allheeling angles.

● Required value. The maximum heeling angle that is allowed.

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Illustration Illustration 11.1711.17: Parameters for the "High speed turning": Parameters for the "High speed turning"criterion.criterion.

DELFTship

12. 12. TransformTransformThe transformation operations described paragraph 12.1, 12.2, 12.3 and 12.4 are intended to be used with aselection. There are two different ways to create such a selection.

1. Select the items manually with the mouse2. Select nothing. As soon as one of the commands below is chosen and no selection exists, the program

shows a window from which you can select the appropriate layers. Then the operation is performed onthe selected layers.

12.1 12.1 ScaleScaleScales (part of) the model. For this operation all selected points are assembled in a list together with all the pointsthat belong to selected edges and faces. If nothing is selected, a window is presented to the user from which entirelayers can be selected. If the checkbox at the bottom of this dialog is checked (the one saying: “include points thatare shared with unselected layers”) then a point is selected automatically if at least one attached face belongs to aselected layer. If the checkbox is not checked, then a point is selected only if all the faces around it belong toselected layer(s). If all the points of the model are selected, then not only is the hull scaled, but all otherinformation such as main particulars, intersection curves, tanks and critical points too.

12.2 12.2 MoveMoveMoves (part of) the model. Works on points extracted from a selection, as described in paragraph 12.1.

12.3 12.3 RotateRotateRotates (part of) the model. Works on points extracted from a selection, as described in paragraph 12.1.

12.4 12.4 MirrorMirrorIn contrast to the previous transformation commands this one is based onselected faces only, not points. First the faces need to be selected that must bemirrored. Only then you can use the mirror command to create a mirrored copyof the selected faces. The mirror plane can be either transverse (YZ plane),horizontal (XY plane) or vertical (XZ plane). The distance of the mirror plane tothe origin must be specified in the distance field. The checkbox at the bottom ofthe form tells the program if the mirrored points should be connected to alreadyexisting points or not.

12.5 12.5 Hullform transformationHullform transformationDELFTship has the ability to automatically adjust some hullform parameters. You can use two different types oftransformation:

● The hullform transformation method developed by Lackenby is used to transform the hull to match adesired displacement or longitudinal center of buoyancy while maintaining fairness of your design. This isdone by shifting control points in the longitudinal direction. So the overall length of the design will bedifferent after the transformation. The window looks as shown in illustration 12.2.

● The midship coefficient transformation adjusts the shape of the hull so that a specified midship coefficientis met. Note that after this transformation the displacement is also altered. If both the midship coefficientand the displacement need to be modified it is advised to adjust the midship first before transforming thehull to the desired displacement or center of buoyancy. The midship coefficient transformation might resultin a distorted deck line.

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Illustration Illustration 12.112.1: Mirror faces.: Mirror faces.

DELFTship

The input fields to the left are divided in 3columns. The left column shows the currentvalues as calculated from the model. The middlecolumn shows the desired values which can bemodified by the user. Depending on whichtransformation method is selected some inputfields can be disabled. The right column showsthe difference between the current and desiredvalues. The left and right column are updatedafter each iteration so the progress can bemonitored.

Below these 3 columns the maximum number ofiterations that may be performed can bemodified. The default is 15, but sometimes moreiterations are needed to obtain the desiredresult. This is specially true when a design has ahigh prismatic coefficient in the aft ship, such asplaning motor craft, or when the midshiplocation is far from the usual place at0.5*Length.

The checkbox below that ensures that all windows of the program are updated after each iteration, so the progresscan be monitored in 3D.

As can been seen on illustration 12.3 is the bodyplan of the original hull displayed in black. If the transformationwas successful then the transformed bodyplan is displayed in red dashed lines on top of the original bodyplan tovisualize the difference between the original and transformed hull.

At the bottom of the window the original sectional area curve and design waterline are displayed, also in black.Again the new sectional area curve and design waterline are displayed on top of these if the transformation wassuccessful. The dark gray dashed line is the location of the midship section as defined by the user in the projectsettings. It is important to know that in contrast to the hydrostatics calculated elsewhere in the program here it iscalculated using ordinates, and not surface panels. This can cause a slight difference between the displacementshown here and calculated elsewhere. A total of82 ordinates is used to calculate the sectionalarea curve and hydrostatics, 41 for the aft shipand 41 for the fore ship.

Finally at the bottom-left corner all layers of themodel are shown. The transformation is onlyapplied to the layers that have a check marknext to them. As stated previously thetransformation consists of shifting control pointslongitudinally, so the location of for example akeel, centerboard or cabin is also likely tochange. By excluding layers from thetransformation they remain unchanged, but itmay result in a distorted or unfair model if themodel was transformed excessively.

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Illustration Illustration 12.212.2: Automatic hull form transformation.: Automatic hull form transformation.

Illustration Illustration 12.312.3: Hull after transformation of displacement.: Hull after transformation of displacement.

DELFTship

13. 13. TankTankss

13.1 13.1 General information about General information about tanktankssTanks are modeled as 3D volumes and described by surfaces, just like thehull shape. The biggest advantage of this is that a higher accuracy isobtained, especially when the volume of a tank is calculated under trim andheel as is the case when intact or damage stability is being calculated. Inorder to be able to create complex shapes, tanks are created from multipleobjects called compartments. To create complex tanks you can use as manycompartments as you like (see illustration 13.1) Tanks and compartmentsmay be deleted by selecting them in the tree and pressing the delete key. It isalso possible to drag a compartment from one tank to another with themouse. Although the compartments are modeled as separate items allcompartments within a tank are treated as one, meaning that the fluid level inall compartments is the same. If one of the compartments of a tank could notbe build properly, both the compartment and tank it belongs to will have anexclamation mark displayed next to them in the tree (illustration 13.2). Thismakes it easy to see if your model contains any invalid tanks. A compartmentshould be fully closed at all sides after it has been build. If this is not the casethe exclamation mark will be displayed and the model contains some purpleedges. These are the edges where the compartment could not be closed. Inthe case of illustration 13.3 the top of the compartment was extended to thedeck while there is no deck in the ship. Therefore the aft, top and front sidecould not be closed. The remedy for this specific case is to either drop the topof the compartment to below the sheer line or to create a deck to make thehull closed.

13.2 13.2 EditEditIllustration 13.4 shows the tank editor window. There is no menu, all edit commands are accessible through thetoolbar at the top. The tree to the right shows allthe available tanks and compartments. Byselecting a tank or compartment a paneldisplayed at the top of the windows shows theproperties of that item. Only the item that iscurrently selected is drawn. If no tank orcompartment is selected all the available tankswill be drawn. This can be done by clicking onthe white area at the bottom or to the right of thetree.

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Illustration Illustration 13.113.1: Tank made out of: Tank made out ofmultiple compartments.multiple compartments.

Illustration Illustration 13.213.2: Invalid tank.: Invalid tank.

Illustration Illustration 13.313.3: Invalid compartment.: Invalid compartment.

Illustration Illustration 13.413.4: Tank editor window showing tanks and compartments.: Tank editor window showing tanks and compartments.

DELFTship

13.2.1 13.2.1 Adding a Adding a tanktankPress the new tank button on the toolbar or the insert key on your keyboard. A new tank will be added to the treeand is automatically selected. The new tank contains 1 compartment by default. You can modify the followingproperties of the tank (illustration 13.5):

13.2.1.1 AbbreviationA short description of the tank. The full description can be changed by clicking on the name of the tank in the tree.

13.2.1.2 GroupAll tanks must be assigned to a weight group byselecting the appropriate group from the drop-downlist. Weight groups are, just as the name implies,groups of weights (or tanks) having the sameproperties. This is especially useful if you have multipletanks with the same contents. To manage the weightgroups you should press the button from the toolbarwith the weight groups icon:

In the weight group window (illustration 13.6) weightgroups can be added, deleted or modified. It alsooffers an overview of how many tanks or weights areassigned to each group. By default all the weightgroups will be shown in the load case editor unless youexplicitly hide them from the load cases. If a weight group is specified as a “lightship” group then all the weightsassigned to this group are added to the lightship weight used in the load case editor.

New groups are added by pressing the insert key on the keyboard. The delete key deletes the selected weightgroup.

Note that the order of weight groups is very important and can be changed by dragging the the first column of aweight group to a new row. The same order of the weight group window is applied when creating the tank overviewand intact stability report.

The last column shows the type of weightgroup. This information is used in the probabilistic damage stabilityextension where the damage permeability of a tank or space is calculated automatically based on this setting.

13.2.1.3 Tank positionThe tank position indicates on what side of ship the tank is located (port, starboard or center). By modifying this allcompartments of this tank will switch to the selected side. You can also modify this on a compartment-level byselecting the appropriate compartment first.

13.2.1.4 Relative densityThe density of the contents of the tank relative to the density of fresh water, which is 1.000. Sea water has arelative density of 1.025.

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Illustration Illustration 13.513.5: Tank properties: Tank properties

Illustration Illustration 13.613.6: Weight group dialog.: Weight group dialog.

DELFTship

13.2.1.5 Intact permeabilityThe intact permeability is the permeability of the tank which is used for calculating the volume when loaded withfluids. Due to the fact that the walls of the tank have a thickness and the presence of construction parts the realinternal volume is always smaller than the volume as calculated from the surface describing the outer side of thetank. Therefore the permeability is always a number between 0.0 and 1.0. By default the permeability is set to0.98. For tanks with few or no internal construction parts this could be set to 0.98-0.99.

13.2.1.6 Damage permeabilityNot used in version 3.3.

13.2.1.7 Non-buoyantThis property enables user to directly connect he selected tank with the surrounding (sea) water. This feature isparticularly useful when modeling non buoyant volumes such as moon pools, bow thrusters or sea chests. Thevolume of all these tanks is automatically subtracted from the displacement and other hydrostatic properties suchas water plane area, sectional area curve etc. The relative density can not be modified since the programautomatically uses the water density as specified in the project settings.

13.2.1.8 Use FSC when slackThe IMO requires that for tanks containing consumables at least from one tank (or one pair of tanks) the freesurface correction is applied to the stability curve, even when the tank is empty. Enabling this option ensures thatthe maximum free surface correction of this tank is applied, even if the tank is empty.

13.2.2 13.2.2 Adding a Adding a compartmentcompartmentYou can add new compartments by selecting the appropriate tank and pressing the new compartment button fromthe toolbar. The new compartment is added to the tank and will be automatically selected.

The following properties of the compartment can be modified:

13.2.2.1 Type of compartmentBasically there are two type of compartments available inDELFTship at this stage.

● Simple. The most frequently used type ofcompartment. The shape of the compartment isdefined as a simple box that is trimmed against the hull(see also paragraph 13.2.2.4 on page 59). The aft,forward, inner, outer, lower and upper boundary of thecompartment must be specified as shown onillustration 13.8. In the input fields you can either enteran absolute value/number or the identifier shell whichtells the program that the compartment extends to theshell.

All compartments are modeled at the port side ofthe ship, so only positive values are accepted in the

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Illustration Illustration 13.713.7: Compartment properties.: Compartment properties.

Illustration Illustration 13.813.8: Input of a simple box compartment.: Input of a simple box compartment.

DELFTship

input field for breadth values. You can switch a compartment from the port side to starboard asdescribed in paragraph 13.2.2.2 on page 58.

● Advanced. In some cases compartments have tilted sides. If you set the compartment type to advancedyou can enter the coordinates of each of the 8 cornerpoints of the compartment's bounding box. For eachside DELFTship fits a plane through the four cornerpoints. This plane is used to build the compartment.

The sides of a compartment that do not extend to theshell are always flat (as in planar), regardless of thevalues specified for the cornerpoints.

A plane is uniquely described by three points inspace. If the fourth point of a side is not exactly onthat plane the best average fitting plane through thefour points is used.

Illustration 13.9 shows the input fields of an advancedcompartment.

13.2.2.2 Compartment positionWhile modeling compartments only positive numbers are allowed for the breadth values. This is due to the fact thatonly 1 side of the hull is physically present in the program. By modifying the compartment position setting you canswitch a compartment to starboard side or both sides of your ship. You can also do this on a tank level asexplained in paragraph 13.2.1.3 on page 56.

13.2.2.3 Positive/negativeSometimes tanks contain recesses that are difficult to model. Infact it might be simpler to model that recess and subtract it fromthe total tank rather than modeling the parts of the tanksurrounding the recess. If a compartment is set to negative allproperties such as volume, COG, free surface moment etc. aresubtracted from the total tank. Be careful not to subtract acompartment from a tank that has a larger volume than the totaltank volume! Negative compartments show up in a differentcolor than positive compartments to make them easier toidentify. In most cases the tank can also be build using onlypositive compartments but is easier to create by using negativecompartments. An example is shown on illustration 13.11where two identical tanks are displayed. The green tank to theleft is made out of 4 positive compartments while the blue tankis made out of only two compartments, 1 positive and one negative(dark red).

By using negative compartments it can sometimes be difficult to seethe actual shape of the tank, especially if multiple negativecompartments are used. By using only positive compartments thiscan be avoided as you always see the true shape of the tank.

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Illustration Illustration 13.913.9: Input of an advanced box compartment.: Input of an advanced box compartment.

Illustration Illustration 13.1013.10: Tank containing negative compartments (in: Tank containing negative compartments (inred).red).

Illustration Illustration 13.1113.11: Two identical tanks build in a different: Two identical tanks build in a differentway.way.

DELFTship

13.2.2.4 Trim at hullNormally compartments are automatically trimmed at the hull. If this is not desirable then you can disable this sothe compartment will have exactly the shape as defined in the input fields. This is especially useful if you want todefine compartments in areas where no hull definition exists, for example when modeling the superstructure as atank.

If one of the input fields contains the value shell then the compartment is automatically trimmed at the shelland this option is disabled.

13.2.2.5 Use all layersBy default all layers are used when building a compartment. If you disable thisoption you'll be able to explicitly define what layers should be used for theselected compartment as described in paragraph 13.2.2.6.

13.2.2.6 SelectThis enables you to select which layers should be used when the selectedcompartment is being build. As stated in paragraph 13.1 a compartment mustbe fully closed along all edges. By carefully excluding layers from the selectingsometimes errors can be avoided. Layers containing boundary edges cansometimes cause problems. Also it might be clear that layers that containitems such as sails, masts etc. should not be included in the selection.

13.2.3 13.2.3 Copy a Copy a tanktank or or compartmentcompartmentYou can copy the selected tank or compartment by pressing the copy button on the toolbar.

13.3 13.3 TankTank arrangement arrangementBy pressing the tool button with the tank arrangement icon you can access the window to create a layout for a tankarrangement. This layout is being used in the load case report to show the filling of tanks. The probabilisticdamage stability has its own tank arrangement layout to visualize the damage cases. By default a tankarrangement contains no views and the grid to the right of the window is empty. Creating a layout can be done intwo ways:

1. Manual. By pressing the Ins key onyour keyboard in the grid to the right anew view is created and added to thelist. A view is a cross section of the 3Dmodel. In the grid you can specify thetype of cross section (plan, profile orbodyplan) and its location with respectto the origin. The views areautomatically sorted when drawn onscreen. The Del. Key can be used todelete a specific view.

2. Automatic. Manually creating a layoutof complex vessels can be very difficultsince generally the goal is to visualizeas much tanks as possible with aminimum of views. DELFTship has the

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Illustration Illustration 13.1213.12: Selecting layers.: Selecting layers.

Illustration Illustration 13.1313.13: Tank arrangement window.: Tank arrangement window.

DELFTship

feature to generate a layout automatically based on a selection of tanks. The option is located in the editmenu from the tank arrangement form. First a window opens where you select one or more weight groupscontaining tanks. Based on this selection 1 profile view on the centerline is added and a number ofbodyplan and plan views. These views are created in such a way that each tank is visible at least once inthe plan views and also in the bodyplan views. Once the layout has been created you can still add, deleteor modify the views manually to adjust it to your needs.

13.4 13.4 Comparison of internal and external geometry.Comparison of internal and external geometry.Another useful feature is the ability to compare the internal and external geometry of the ship. This feature can beused to spot areas in the ship where the internal volume occupied by tanks is smaller or larger than the volume ofthe hull. This can be used to track down errors in the tank definition.

13.5 13.5 OverviewOverviewIllustration 13.14 shows an example of the report that is produced by the tank overview option. Here you canclearly see the use of weight groups as explained in paragraph 13.2.1.2 on page 56. Tanks are grouped accordingto their weight group presented in the same order. If a tank arrangement layout has been created (see paragraph13.3 on page 59) then it will also be included in the report.

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Illustration Illustration 13.1413.14: Example of the tank overview report.: Example of the tank overview report.

DELFTship

14. 14. Load caseLoad casess

14.1 14.1 General information about General information about load caseload cases.s.A load case is in fact nothing but a collection of weights and related centers of gravity. These weights can be fixed(point) weights but also tanks that are (partially) filled or weights from a common weight list. The sum of alle theseweights equals the displacement of the ship. When the load case is being solved DELFTship tries to establish theposition of the ship in the water for a number of heeling angles. Using this information the program calculates thedraft, trim and heeling angle for the equilibrium state and also the stability curve. There's no restriction when itcomes to the number of load cases. They show up in the drop down list left in the toolbar. You can select theappropriate load case from this list.

14.2 14.2 EditEdit

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Illustration Illustration 14.114.1: Load case editing window.: Load case editing window.

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Illustration 14.1 shows an overview of the load case window. It can be subdivided into the following 5 main areas:

1. A 3D view on the model is displayed at the top. Themodel is initially shown in a level position. Once theload case has been solved and an equilibrium couldbe established the model will be drawn in thatposition. The submerged areas of the hull areshaded in a different color. You can choose betweena shaded view of the hull or a wireframe view whichoffers a better view on the the contents of tanks.Both views are shown on illustration 14.2. Theamount of transparency for shading hull surfacescan be adjusted in the preferences window(paragraph 8.6 on page 27).

2. The input area is where most of the action takesplace. The top item shows the lightship weight andcenter of gravity. This special weight item can not bemodified or deleted. It adds up all the weights fromthe various weight groups which have been markedas being part of the light ship. Below the light shipitem all the other weight groups are displayed.

The dark gray rows are the headers of each weightgroup and they display a summary for each weightgroup. This way you can instantly see how muchballast water or HFO has been loaded for example.The first column of each header contains the description of that particular weight group. By pressing the [-]or [+] sign next to this description the weight group can be collapsed or expanded for a clearer view on allitems of this load case. Weight groups can be hidden from a load case or the order of appearance can bemodified in the weight group dialog (see also paragraph 13.2.1.2 on page 56).

Only the data in the light gray cells can be modified by the user. The other cells contain calculated data.The two rightmost columns show the aft and forward boundary of each weight. These boundaries arerelevant only to determine the longitudinal weight distribution for determining the longitudinal bendingmoments and shear forces (see paragraph 14.2.8 on page 66). If the bending moment extension is notincluded then the data is irrelevant and those two columns will not be visible to the user.

3. A summary of all the specified weights is shown justbelow the input area. It shows a summary forlightship, deadweight and total displacement.

4. Next to the weight summary details on the equilibriumposition are displayed. All relevant data is shown,including the applied free surface correction and themaximum allowable VCG for the selected stabilitycriteria if that extension is included into the software.

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Illustration Illustration 14.214.2: 3D view on load case.: 3D view on load case.

Illustration Illustration 14.514.5: Equilibrium properties.: Equilibrium properties.

Illustration Illustration 14.314.3: Input area: Input area

Illustration Illustration 14.414.4: Summary of weights: Summary of weights

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5. The final area shows two tab pages that either showthe numerical results for each heeling angle or thestability curve. By default the tab page with thestability curve is selected. The actual appearance ofthe graph depends on the settings for the selectedset of stability criteria as every single criterion of theset can be plotted in the curve or hidden. For moreinformation on the use of stability criteria the user isreferred to paragraph11.11 on page 46.

14.2.1 14.2.1 Using the Using the weight listweight listThe weight list is a convenient way to manage lightship itemsand common weights that occur in multiple loadcases. Allweights in the weight list are added to a weight group. Allweights added to a weight group which is marked as alightship group are automatically added to the lightshipweight. In some cases specifying a single weight for thelightship item suffices. However if you want to calculate thelongitudinal bending moment and shear force the lightshipmust be subdivided in as many known weights as possible.The aft and forward boundaries of each weight must bespecified also since it is used to generate the longitudinalweight distribution. (see also paragraph 14.2.8 on page 66) Ifthe longitudinal center of gravity of a weight is outside therange of 1/3 – 2/3 of the length between the aft and forwardboundary of a weight then the cells containing the values forthese boundaries are displayed in red to indicate that there might be a mistake in the input.

At the top of the input window a list is shown with all the available weight groups. The main area of the windowshows all weights added to the selected weight group. You can add new weights by pressing the insert (ins) keyon your keyboard while the delete (del) key will delete a weight. The order of weights can be modified by draggingthe number displayed in the leftmost column to a new row. With the Ctrl-C and Ctrl-V shortcuts you can quicklycopy and paste properties from one weight item to another.

14.2.2 14.2.2 Editing Editing load caseload casess

14.2.2.1 Add a new load case.By pressing the new load case button from the toolbar a new load case is added. By default it contains the lightship item and all weight groups, which are still empty at this stage. Since all weights belong weight groups youmust first select the header of a weight group to which you want to add the new weight. By pressing the insert (ins)key on your keyboard a new weight wil be added to the selected weight group. Weights can be deleted again byselecting the row containing the weight to be deleted and pressing the delete (del) key. Only the light ship item andthe weight groups can not be deleted.

14.2.2.2 Modify the load case nameThe name of the load case is displayed in the input field right next to the list with all load cases. The name of the

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load case can be altered in this field.

14.2.2.3 Selecting a wind silhouetteNext to the load case name there is a list that contains all the wind silhouettes that have been defined (see chapter14.3). You can select one of these silhouettes and assign it to the active load case. The wind moment caused bythis silhouette will be calculated and validated against the selected stability criteria. Editing stability criteria iscovered in paragraph 11.11 on page 46.

14.2.2.4 Adding weightsAll weights from a load case must be assigned to a weight group. To add a new weight first select the header ofthe weight group and then press the insert (ins) key on your keyboard. DELFTship identifies three different type ofweights:

1. Fixed weights. Mostly these are weights that only occur once in all load cases.

2. Tanks.

3. Weights from a list with common weights. If you have weight items that occur in multiple load cases thenyou can add those weights to the weight list. (see paragraph 14.2.1)

By default new weights are set to the “fixed weights” (see also paragraph 14.2.2.5)

14.2.2.5 Modifying the different types of weightsThe second column of each weightcontains a drop down button. Oncepressed you can select the new weighttype from the list. The following differenttypes of weights are available:

● Fixed. Fixed weights are weightsrepresented by a point in space.

● Tank. Tanks containing liquids that is allowed to move under heel and trim.

● Fixed tanks. Tanks containing solid loads that will not move when heeled. Examples are lead ballast in asailing yacht or homogeneous cargo in the hold of a general cargo ship.

● Weightlist. Any weight from the weight list that is not part of the light ship weight.

If the weight type is set to “tank” or “weight list” then the first available item from the weight group is automaticallyassigned to the selected weight.

Note: Tanks or weights from the weight list (paragraph 14.2.1 on page 63) can only be assigned once to each loadcase.

14.2.2.6 Selecting a tank or a weight from the weight listAssigning tanks or weights from the weight list is very similar to the process of changing the weight type. If thedrop down button in the first column ispressed then a list is shown with all thetanks (or weights) belonging to theselected weight group. If the list is emptyit might be for one of the followingreasons:

1. There are no tanks or weightsassigned to the selected weightgroup (paragraph 14.2.1 on page

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Illustration Illustration 14.614.6: Selecting the type of weight.: Selecting the type of weight.

Illustration Illustration 14.714.7: Selecting a tank or weight from the weight list.: Selecting a tank or weight from the weight list.

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63).

2. All of the tanks or weights from the weight group are already in use in the load case.

14.2.2.7 Add all tanksEspecially if a project contains a large number of tanks it can be a tedious job to add all the tanks one by one.Therefore the special option “Add all unused tanks” that is accessible through the toolbar menu by pressing the

button will do this for you.

14.2.3 14.2.3 Deleting a Deleting a load caseload caseYou can delete the selected load case by pressing the button with the recycle bin from the toolbar.

14.2.4 14.2.4 Copy a Copy a load caseload caseThe copy option creates an exact copy of the currently selected load case.

14.2.5 14.2.5 Solve a Solve a load caseload caseThe solve button (or pressing the F9 key on your keyboard) initiates the calculation procedure. Load cases thathave been calculated but have been modified afterwards are automatically reset. After the load case has beensolved and an equilibrium has been found the hull and weight items are drawn in the equilibrium state. Thesubmerged surfaces are shaded accordingly.

14.2.6 14.2.6 Show reportShow reportYou can only view the load case report if the load case has been solved. The short report (paragraph 8.6 on page27) only shows a summary of all the weight items while the extensive report displays also a summary for eachindividual weight group. It is possible to indicate which items should be shown in the report and in what order. Thisis done in the file preferences window as covered in paragraph 7.6 on page 24. If a layout for the tankarrangement has been created (see paragraph 13.3 on page 59) then it will be included in the report to show theloading of tanks.

14.2.7 14.2.7 Interpreting resultsInterpreting resultsGZ can be calculated according to theformula displayed on image 14.8. Note thatthe value used for the free surface correction(GG') varies with the heeling angle in case aload case has been calculated with theactual center of gravity for tanks containingfluids.

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Illustration Illustration 14.814.8: Calculation of GZ: Calculation of GZ

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14.2.8 14.2.8 Bending moment and shear force calculationsBending moment and shear force calculationsIf the software includes the bending moment extension then thecalculations are started by pressing the button from the toolbarcontaining the bending moment icon or by pressing the F10 key onyour keyboard.

In order to be able to perform the still water bending moment calculation alongitudinal distribution of all weight and buoyancy forces has to becreated. The weight forces are taken from the weight list and loadcases,while the buoyancy forces are calculated from the sectional area curve.The sectional area curve is calculated for the equilibrium position of theload case, therefore the load case must be solved first.

DELFTship creates a trapezoidal weight distribution for each weight fromthe load case based on the specified weight, center of gravity, aft boundaryand forward boundary (see illustration 14.9). The shape of this weightdistribution is rectangular if the center of gravity is exactly in the middle ofboth the aft and forward boundaries (top image). The distribution istrapezoidal if the center of gravity lies withing 1/3 and 2/3 of the lengthbetween the aft and forward boundaries (second image). If the center ofgravity lies exactly on 1/3 or 2/3 of the length between the boundaries thena triangular distribution of the weight is used. Finally if the center of gravityis outside the 1/3 or 2/3 limit than the uniform weight distribution as shownin the bottom part of the image is used.

Clearly this is not a valid distribution as the weight near the aft boundarybecomes negative and is subtracted. The software will display a warningfor all invalid weight distributions that are encountered during thecalculation process. Most of the times the invalid distribution is caused byerroneous values for either the center of gravity, the aft boundary or theforward boundary. In case the center of gravity really is outside the1/3-2/3 range and a trapezoidal distribution cannot be used it is best tosplit the weight in multiple items in order to create a valid distribution.This is shown on illustration 14.10.

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Illustration Illustration 14.1014.10: Valid distribution by splitting: Valid distribution by splittingthe weightthe weight

Illustration Illustration 14.914.9: Uniform weight distributions: Uniform weight distributions

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Illustration Illustration 14.1114.11: Graph showing wind silhouette, weight distribution, sectional areas, load, shear forces and bending moment.: Graph showing wind silhouette, weight distribution, sectional areas, load, shear forces and bending moment.

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14.3 14.3 Wind Wind silhouettesilhouetteA wind silhouette is a graphical representation of the projected outer contour of the vessel which is used todetermine the moment exerted by the wind on parts of the ship that are above the water. As shown on illustration14.12 the wind area of cargo ships can be considerable.

Another application would be to calculate sail areas or the lateral area and center of effort at various drafts for asailing yacht.

Wind silhouettes can also be assigned to load cases in which case the wind moment is validated against theselected stability criteria.

The right side of the input window can be subdivided into 3 different areas:

• The top area shows the numerical properties for the selected wind silhouette, such as wind area, lateralarea, center of effort etc. You can also specify the area of bilge keels here and the bilge type. This is onlyused to calculate the rollback angle for the standard IMO wind criterion as defined in the IMO A.749resolution.

• The middle part contains a tree-structured list with all the wind silhouettes. Each silhouette may consist outof multiple sub-items, each one representing a closed contour. This way you may build up complexsilhouettes, for example by modeling each sail of a sailing yacht as an individual sub-item. DELFTshipidentifies two different types of sub-items: hull or sail. Sails are treated differently in order to be able tocalculate sail area, center of effort and lead. Also, areas of sails that become submerged at large angles ofheel are not included into the lateral area.

• Below the list with silhouettes a grid is displayed that shows the coordinates of the currently selected sub-item. You can insert, delete or modify these coordinates manually but you can also drag the coordinateswith the mouse on your screen.

Using the toolbar at the top you can:

1. Export and import silhouette data to or from a file

2. Create new silhouettes

3. Add new items to a silhouette

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Illustration Illustration 14.1214.12: Definition of wind silhouettes: Definition of wind silhouettes

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4. Create a copy of the currently selected silhouette or sub-item. A copy of a sub-item can be moved toanother silhouette by dragging it with the mouse.

5. Print a silhouette

14.3.1 14.3.1 Adding a new wind Adding a new wind silhouette.silhouette.Make sure no wind silhouette or sub-item is selected. You can do this by clicking on the white space in the list withwind silhouettes. Press the Ins key to insert a new wind silhouette or press the appropriate button on the toolbar.DELFTship automatically extracts a new silhouette from the current model. Usually if the model is not too complexit consists of a single sub-item. In other cases multiple sub-items can be generated. Some of these may beobsolete and can easily be deleted.

14.3.2 14.3.2 Modifying wind Modifying wind silhouette datasilhouette dataOnce a wind silhouette is selected, the corresponding data is shown and can be modified. The bilgekeel area andtype is only relevant for IMO stability criteria (see paragraph 11.11.10 on page 50). The name of a wind silhouettecan be modified by clicking on it with the mouse which causes the list to drop into editing mode. Once the enterkey has been pressed the new name will be assigned to the wind silhouette. Altering the name of sub-items isdone the same way. New sub-items are added by pressing the ins key on your keyboard. A selected sub-item (orwind silhouette) is deleted by pressing the del key. The coordinates of a selected sub-item are shown in the grid.Again coordinates are added or deleted by pressing the ins or del key.

14.4 14.4 Wind moment calculationWind moment calculationThe wind moment calculation window shows a list with all theavailable wind silhouettes. Apart from the range of drafts you canselect the appropriate silhouettes and specify a wind pressure. Thedefault wind pressure is 51.4 kg/m2 which is the standard IMO windpressure for most vessels. For each draft the lateral area, windarea, wind lever and wind moment is calculated and displayed in areport.

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Illustration Illustration 14.1414.14: Input screen for the calculation of wind: Input screen for the calculation of windmoments.moments.

Illustration Illustration 14.1314.13: Example of a wind silhouette.: Example of a wind silhouette.

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15. 15. ViewView

15.1 15.1 IntersectionsIntersectionsIntersection curves are calculated from the surface model. Only theirlocation needs to be specified. Diagonals are always at an angle of 45degrees to the center plane. Each time the model is modified theintersection curves are dynamically recalculated and updated. Thebuttons on the toolbar will let you switch between the different types ofintersections you want to add or delete. You can add one intersection ata time by selecting the +1 option in the menu. A window is displayedasking for the location of the intersection. It is also possible to add awhole range of intersections by pressing the +N option. In that case thelocation of the first and last intersection are requested as well as thespacing between the successive intersection curves. If an intersectionwith a surface has been found then it will be added to the model. Theintersection curves appear in an increasing order of their location withrespect to the origin. To delete a single intersection, just select it and press the delete key onyour keyboard. All intersections in the currently selected group can deleted in one pass by pressing the recycle bin button on thetoolbar.Next to the recycle button there's another button on the toolbar that will let you convert all the intersections fromthe currently selected group into markers.

The checkbox displayed to the left of each intersection indicates if the curvatureplot of that specific intersection curve must be plotted (see also paragraph 9.7.1on page 34) Due to the limited size of the computer screen it is almostimpossible to determine if a curve is fair. To overcome this a curvature plot isoften drawn. A curvature plot means that in a large number of points of a curvethe curvature is calculated and plotted perpendicular to the curve ( the purpleline). Since the curvature can be positive as well as negative, the plot can swapfrom one side of the curve to the other (illustration 15.2). Where the plotcoincides with the curve the curvature is zero. So in areas of a curve where the.At a knuckle point on the other hand the curvature is infinitely high. So thehigher the absolute value of the curvature, the further the curvature plot is drawnaway from the curve. Smooth curves are characterized by curvature plots withno unexpected humps or hollows. The scale of the curvature plot can bedecreased by pressing the F9 key and increased by pressing the F10 key. Make

sure that the curvature plot is switched on in you the display settings.

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Illustration Illustration 15.215.2: Curvature plot of a: Curvature plot of abuttock.buttock.

Illustration Illustration 15.115.1: Intersections window.: Intersections window.

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15.2 15.2 LinesplanLinesplan

DELFTship enables the user to view the complete formatted linesplan of the ship. This can be done in two differentmodes, wireframe mode (to the left) and the filled mode (to the right). The linesplan shows all the intersectioncurves, regardless of the display settings of the corresponding intersection curves. So stations are always shownin the linesplan, even if they are switched off in the display settings. Currently this linesplan can be saved as abitmap, to a dxf file, or sent directly to the printer/plotter. The linesplan can also be drawn in black & white byclicking on the appropriate button in the toolbar. Using fill colors is not possible in black & white mode. Only if themodel contains no diagonals, the plan view might optionally be mirrored so that both sides are visible. Some layerscan be hidden from the linesplan. How this is done is described in paragraph 9.8.1.

15.3 15.3 Design Design hydrostaticshydrostaticsAn elaborate hydrostatic calculation is performed of the ship at thedesign draft, as specified in the project settings (paragraph 8.2) andwith level trim. The way coefficients are calculated and how to modifythis is explained in paragraph 8.3. The report does not only showhydrostatic properties but also the surface area and center of gravityfor each layer. All properties are calculated for the entire ship. If themodel contains stations then the sectional area curve is also plotted.

If imperial units are used, the displacement is given in longtons (1long ton equals 2240 lbs).

15.4 15.4 HydrostaticsHydrostaticsThis option is used to perform hydrostatic calculations at a range ofdrafts. An initial trim can also be specified in the professional version ofDELFTship. In addition the professional version shows some extradata that is not displayed int the free version of software. The reportcan be fully customized (see paragraph 7 page 24) and sent to eitherthe printer or saved to a HTML file. Illustration 15.4 shows an exampleof the produced output.

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Illustration Illustration 15.315.3: Example of default linesplan output.: Example of default linesplan output.

Illustration Illustration 15.415.4: Hydrostatics report.: Hydrostatics report.

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15.5 15.5 Inclined Inclined hydrostaticshydrostaticsThe inclined hydrostatics extension offers the designer a viewon the hull for a user specified heeling angle, trim anddisplacement. The displacement corresponding to the designdraft is used as an initial value. The software will calculatethe corresponding draft and display the hull and (heeled)waterlines. The extension is not only useful to optimize theshape of sailing yachts in order to minimize the amount oftrim that occurs while the ship heels, it can also be used tovisually check when the deck edge submerges. The amountof waterlines to be displayed can be in the range from 0 to25. A regular spacing between the waterlines is used. Next tothe 3D view the most important hydrostatic features of thespecified condition are displayed.

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Illustration Illustration 15.515.5: Inclined hydrostatics.: Inclined hydrostatics.

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15.6 15.6 CrosscurvesCrosscurvesIf the optional crosscurves extension is included into thesoftware then stability calculations are also provided in theform of cross curves. For a number of heeling angles, trimsand displacements KN*sin(ø) is calculated and presented inboth graphical and tabular form. If only one singledisplacement is specified KN*sin(ø) curve is displayed. Ifmultiple displacements are provided the graph shows thestandard graph for cross curves as can be seen on illustration15.6. The crosscurves are calculated while the hull is free totrim. For each displacement the calculation is started with thespecified initial trim and subsequently for each heeling anglethe trim is adjusted to maintain a constant center ofbuoyancy. In combination with the critical points extension thereport also shows a tabulated downflooding overview. Foreach heeling angle the first submerged downflooding point isdisplayed in combination with the correspondingdisplacement. Other options are:

● Extended report or a simplified report. ● Heel to port/starboard, especially useful for

asymmetrical hulls.

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Illustration Illustration 15.615.6: Example of crosscurves report.: Example of crosscurves report.

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15.7 15.7 Max VCGMax VCG''The max VCG' extension calculates the maximum verticalcenter of gravity for each stability criterion for which thatcriterion still passes. This is done for all the criteria from theselected set of stability criteria. The criterion with the lowestvalue for the VCG is the limiting criterion. It is calculated fora range of drafts, trims and wind silhouettes. For eachcombination of draft, trim and silhouette a stability curve isgenerated and the criteria will be evaluated. Due to themany combinations possible it can be a time consumingcalculation. The report shows a graphical representation ofthe calculations, called limiting VCG' curves, as well as thetabulated numerical results. The green area in the graphindicates the “safe area”. The red area on the other hand isthe “unsafe area”. VCG values in the red area will result afailed test for the stability criteria.

If the selected criteria contains the wind criterion then atleast one wind silhouette must be selected also. For eachspecified draft the actual wind area is calculated from thesilhouette.

For more information on selecting or creating a set ofstability criteria the reader is referred to paragraph 8.6 onpage 27 and paragraph 11.11 on page 46.

15.8 15.8 Plate developmentPlate developmentssAll layers that are marked as developable in the layer properties window (paragraph 9.8.6 on page 37) areunfolded into flat plates (a process also called developing). If the model contains no developable layers then thisoption is disabled in the menus. Both sides of the ship will be unfolded. A window then is opened showing the platedevelopments. It is best to assign each strake or part of the hull to a different layer. Then each layer will have itsown unfolding. If a layer consists of multiple isolatedparts, each part again will have its own unfolding.The unfolded panels can be moved by draggingthem with the mouse. Buttons on the toolbar at thetop of the window can be used to rotate thecurrently selected plate. The rotation angle of eachpanel may additionally be entered manually.Zooming and panning is done exactly as in thewindows used for modeling the ship. Interior edgesor any present intersection curves are drawn on topof the unfolded panels, and can be switched on oroff as desired. The initial display settings are thesame as the display settings from the mainmenubut can be modified. The image displayed in theviewport be can saved as a bitmap image, butvisible plate developments can also be exported toa .dxf file or sent directly to the printer/plotter. Thecoordinates forming the outer boundary of each partcan be exported to an ASCII text file.

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Illustration Illustration 15.715.7: Plate developments.: Plate developments.

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To the right of the window a list is visible with all the unfolded parts. By clicking on the check boxes each platedevelopment can be made visible or invisible. At the top some crucial information about the developments isshown. After the plates have been unfolded to 2D, DELFTship compares the length of the unfolded interior edgesto the length of these edges in 3D. If this length is smaller then the edges are compressed (drawn in blue). If theunfolded edges are longer then these edges are stretched (drawn in red). The minimum error shown at the top isthe largest compression error that occurred (in world space dimensions, so meters or feet). The maximum error isthe largest amount of stress of an edge. Compressed or stretched edges may be visualized by turning both thevisibility of interior edges and highlighting of compressed edges on. The difference in area between the 3D surfaceand the unfolded surface is also shown. Below the displayed edges the number of iterations it took to unfold theselected panel is shown. DELFTship makes up to 25 developments of each panel and uses the one with thesmallest overall error as the final one. Generally surfaces that are truly developable are unfolded in 1 iteration, andhave min. and max. errors of 0.0. Surfaces that are not exactly developable can in most cases still be unfolded butmight have significant errors due to the fact that the surface is curved in two directions. Think of it as the top half ofa sphere, you can not press this surface down to a flat surface without stretching or compressing certain areas,unless you make some cuts in the surface. So it's very important to check these errors if you actually want to usethe unfolded plates for construction purposes!

There are also two input fields to adapt the grid spacing. The grid can be turned on and off from the toolbar. Eachintersection of a grid line and an unfolded panel has a number displayed next to it indicating the coordinate of thatintersection.

The two panels that are created from layers that border the center plane of the hull and are completely flat, suchas for example a flat transom or bottom, are merged into 1 unfolded panel.

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15.9 15.9 ResistanceResistanceDELFTship currently contains twomethods to predict the resistance of amodel. The resistance module is createdsuch that all data relevant to the differentprediction methods only needs to bespecified once and is shared by all ofthose methods. This way optimalconsistency is ensured and the requiredamount of user input is kept to aminimum. To make things easier mosthullform parameters can be extractedautomatically from the model. Of courseit is also possible to enter thoseparameters manually. The first tab pagecontains a list with all the methods that are available. By clicking on the check box next to the name of eachmethod that particular method can be included or excluded from the calculations. You can easily compare theresults of different methods by plotting them simultaneously in the resistance graph as shown on the image above.

This resistance module has been completely rewritten in preparation of the addition of more resistance predictionalgorithms that will be added with the next release.

The report button shows the numerical results from the calculations for the selected prediction methods in a singlereport.

15.9.1 15.9.1 Delft seriesDelft seriesThe Delft series resistance calculation is a method that is intended for fin-keeled yachts. From version 3.2 and upthe results are based on a the publication from 1998. It's a statistical method based upon a whole series of modelsthat are tested over the years in the towing tank of the Delft University of Technology. The software does notrestrict the calculations to use only models that that are in the same range as those of the tested models. Resultsof models that are outside the range however can be very inaccurate with sometimes even negative results for theresidual resistance.

15.9.2 15.9.2 KaperKaperThe KAPER resistance method is intended for canoes and kayaks. It was originally developed by John Winters, anaval architect now specializing in designing canoes and kayaks. (See http://www.greenval.com/jwinters.html) It isbased on statistical data obtained by model tests. His method is later extended by Matt Broze to higherspeed/length ratios and to incorporate more variables into the equations. This extended version is available in theform of an Excel spreadsheet from http://www.marinerkayaks.com/mkhtml/downloads.htm. However whileimplementing this method in DELFTship two serious discontinuities showed up in the curve of residual resistance.These consist of a sudden drop in resistance of about 10% at speed/length ratios of 1.4 and 1.6 and are the resultof a correction implemented by Matt. After careful consideration the decision was made to only allow calculationsup to a speed/length ratio of 1.4 in order not to give the user a false sense of accuracy.

The range of valid parameters for the KAPER method is:● Prismatic coefficient 0.48-0.64● Submerged transom ratio 0.0-0.04● None of the other variables other than the waterline entrance angle is allowed to be zero.

The center of buoyancy used in the Kaper method is measured from the bow and made dimensionless bydividing the distance by the waterline length.

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15.10 15.10 Probabilistic damage stabilityProbabilistic damage stability..

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16. 16. SelectionSelection

16.1 16.1 Selecting objects in DELFTshipSelecting objects in DELFTshipSelecting objects in DELFTship is pretty straightforward. Almost any visible object in the hull modeling windowscan be selected by clicking on it with the mouse. Clicking it again will deselect it. Only critical points (paragraph8.4) can not be selected this way. Selecting works only when the windows are in the wireframe mode (shadingmust be turned off). Selected objects are highlighted in yellow.

For some objects there are some additional ways of selecting which can make life easier:

● Points. If a point is selected, and the user clicks on a different point, this new point will be selected andthe previous point will be deselected. Selecting multiple points however is possible by keeping the CTRL-key pressed while selecting the new point.

● Edges. If the CTRL key is pressed while an edge is being selected, the program tries to trace the edgeuntil a irregular point is encountered or an edge with a different crease-property. This way it is easy toselect an entire row of edges (edge loop) such as for example the sheerline or a hard chine.

● Faces. Faces also can be CTRL-selected. In that case all the faces belonging to the same layer andconnected to the selected one are also selected or deselected. Faces that are isolated from the selectedface because they are totally surrounded by crease edges are not included.

16.2 16.2 Select allSelect all

With this command (also available by pressing the shortcut Ctrl-A) all visible objects are automatically selected.

16.3 16.3 Deselect allDeselect allUse this option to deselect all selected items simultaneously. Pressing the Esc-key has the same result.

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DELFTship

Alphabetical IndexAAAppendage coefficient..............................................................................................................................................................................................26Automatic fairing...........................................................................................................................................................................................30, 35, 44BBB-Spline............................................................................................................................................................................................................6, 9, 17Background image..............................................................................................................................................................................2, 15, 16, 23, 41Box..........................................................................................................................................................................................2, 26, 37, 45, 57, 58, 76CCCompartment................................................................................................................................................................................3, 55, 56, 57, 58, 59

Position...........................................................................................................................................................................................................3, 58Control curve........................................................................................................................................................2, 13, 18, 29, 30, 34, 35, 39, 41, 42Controlnet.................................................................................................................................................................................................2, 13, 39, 44Coordinate system..........................................................................................................................................................................................2, 10, 14Critical point..........................................................................................................................................................2, 26, 27, 41, 44, 47, 48, 53, 73, 78Cross curves.......................................................................................................................................................................................................27, 73Cross curves,............................................................................................................................................................................................................27Curvature................................................................................................................................................................2, 7, 14, 15, 34, 35, 37, 41, 42, 70

Plot.............................................................................................................................................................................................34, 35, 41, 42, 70Cylinder.................................................................................................................................................................................................................2, 45DDDamage stability...........................................................................................................................................................................................................

Probabilistic........................................................................................................................................................................2, 3, 27, 28, 56, 59, 77Deck line.....................................................................................................................................................................................19, 27, 34, 43, 47, 53Downflooding....................................................................................................................................................................................26, 48, 49, 51, 73Draftmark..................................................................................................................................................................................................................25Drawing mode.......................................................................................................................................................................................................2, 14EEEdge..............................................................................................................................................................................................................................

Boundary............................................................................................................................................................................7, 9, 30, 31, 32, 43, 59Crease............................................................................................................................................................................2, 7, 8, 18, 30, 32, 36, 78Interior....................................................................................................................................................................................2, 33, 36, 39, 74, 75

Entrance angle..........................................................................................................................................................................................................76Extrude..................................................................................................................................................................................................................2, 31FFFairing.................................................................................................................................................................................................2, 30, 34, 35, 44

Automatic...............................................................................................................................................................................................30, 35, 44Flowline...............................................................................................................................................................................................2, 13, 29, 39, 41Free surface............................................................................................................................................................................................57, 58, 62, 65Freeboard.......................................................................................................................................................................................................2, 27, 47HHHydrostatics...........................................................................................................................................2, 3, 9, 24, 25, 26, 37, 38, 40, 43, 54, 71, 72

Inclined...............................................................................................................................................................................................3, 25, 38, 72Settings...............................................................................................................................................................................................................25

IIIncremental distance.................................................................................................................................................................................................14Inesplan....................................................................................................................................................................................................................38Intersection curve.........................................................................................................................................13, 37, 38, 39, 41, 42, 44, 53, 70, 71, 74

Buttock......................................................................................................................................................................................................2, 37, 40Diagonal.......................................................................................................................................................................................2, 37, 40, 70, 71Station........................................................................................................................................................2, 9, 17, 19, 25, 37, 38, 40, 42, 44, 71Waterline........................................................................................................................................................2, 19, 25, 37, 39, 40, 41, 54, 72, 76

KKKnuckle line..........................................................................................................................................................................................7, 8, 15, 32, 34LLLayer.............................................................................................................................................................................................................................

Active..................................................................................................................................................................................................2, 31, 36, 45Leak point.................................................................................................................................................................................2, 9, 26, 37, 40, 41, 43Linesplan..........................................................................................................................................................................3, 15, 16, 25, 37, 38, 39, 71Load case....................................................................................................................2, 3, 24, 25, 27, 46, 47, 50, 56, 59, 61, 62, 63, 64, 65, 66, 68Lock....................................................................................................................................................................................................................31, 46MMMargin line................................................................................................................................................................................................................27Marker..................................................................................................................................................................2, 18, 26, 29, 31, 35, 42, 44, 45, 70Max VCG......................................................................................................................................................................................3, 27, 46, 47, 50, 74

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DELFTship

Mesh...........................................................................................................................................................................................6, 8, 9, 32, 33, 37, 39NNNormal...........................................................................................................................................................................................................................

Direction...................................................................................................................................................................................................9, 26, 33NURBS.................................................................................................................................................................................................................6, 45PPPermeability..................................................................................................................................................................................................................

Damaged..................................................................................................................................................................................................3, 56, 57Intact...............................................................................................................................................................................................................3, 57

Plate development..................................................................................................................................................................3, 13, 25, 37, 38, 74, 75Point..............................................................................................................................................................................................................................

Corner...................................................................................................................................................................................................................7Critical............................................................................................................................................................2, 26, 27, 41, 44, 47, 48, 53, 73, 78Leak....................................................................................................................................................................................2, 9, 26, 37, 40, 41, 43Lock................................................................................................................................................................................................................2, 31Regular.........................................................................................................................................................................................................34, 78Unlock.......................................................................................................................................................................................................2, 31, 46

Probabilistic damage stability...................................................................................................................................................2, 3, 27, 28, 56, 59, 77Project settings...........................................................................................................................................2, 9, 10, 19, 25, 40, 43, 46, 51, 54, 57, 71RRRegistration code........................................................................................................................................................................................................5Regular grid..........................................................................................................................................................................................................9, 32Resistance............................................................................................................................................................................................................3, 76

Delft................................................................................................................................................................................................................3, 76Kaper..............................................................................................................................................................................................................3, 76

SSShading.........................................................................................................................................................................................................................

Developability.....................................................................................................................................................................................................14Gaussian curvature......................................................................................................................................................................................14, 15Wireframe...................................................................................................................................................................................14, 39, 62, 71, 78Zebra..................................................................................................................................................................................................................15

Stability criteria.........................................................................................................................................................27, 46, 47, 62, 63, 64, 68, 69, 74Stability curve.............................................................................................................................................................................27, 46, 57, 61, 63, 74Subdivision surface................................................................................................................................................................................2, 6, 7, 31, 41TTTank.....................................................................................................2, 3, 13, 14, 24, 26, 27, 29, 42, 53, 55, 56, 57, 58, 59, 60, 61, 62, 64, 65, 76

Abbreviation.............................................................................................................................................................................................3, 27, 56Arrangement.......................................................................................................................................................................................3, 59, 60, 65Connection.........................................................................................................................................................................................................27Non-buoyant.............................................................................................................................................................................................3, 26, 57Position...........................................................................................................................................................................................................3, 56

Tank arrangement....................................................................................................................................................................................3, 59, 60, 65Tank connection........................................................................................................................................................................................................27UUUnlock.............................................................................................................................................................................................................2, 31, 46WWWeathertight..............................................................................................................................................................................................................26Weight...........................................................................................................................................................................................................................

Group...................................................................................................................................................................................56, 60, 62, 63, 64, 65List................................................................................................................................................................................................3, 61, 63, 64, 66

Wind..............................................................................................................................................................................................................................Moment........................................................................................................................................................................................3, 50, 64, 68, 69Silhouette.........................................................................................................................................................................3, 50, 51, 64, 68, 69, 74

YYYdrostatics................................................................................................................................................................................................................37

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