Boat Hull Design Kit - · PDF file4 Boat Hull Design Kit User Guide 57911 V0311 Before cutting...

57911 V0311

User Guide

Boat HullDesign Kit

2 Boat Hull Design Kit User Guide 57911 V0311

Hull – Nautical. The frame or body of a ship, exclusive of masts, engines, or superstructure.

One of the most exhilarating moments of the design process is the moment when you sit before a completely new, untouched block of material and realize that what you make of it is entirely up to you and your own creativity! That moment is right now, as you begin the process of designing your own boat hull.

This instruction manual will guide you through the boat hull design process. By following these procedures, you transform your ideas into a boat hull to test and use. But be aware that in boat design, there is no such thing as the perfect boat. Every design represents a compromise that takes into account all the various needs and functions the boat must meet.

First, you make many sketches before deciding on a final hull design. Then you learn some of the techniques involved in hull carving by making a prototype from foam. After testing and modifying the design of the foam prototype to your satisfaction, you are ready to make, test, and finish a final wooden boat.

People have been designing boats for centuries. Each new shape is an effort to gain a bit more speed, cargo capacity, safety, and comfort. While following these instructions, you learn the design process and likely build a better boat as well.

Remember, no boat designer lasts long in this business without working safely. Be sure you know how to operate the necessary tools properly and safely.

Introduction

Deck(any horizontal

surface in a boat)

Hold(area designated

for cargo)

Gunwate(top edge

of hull)

Stern(structural piece

that forms the bow)

Waterline

Bow (front)

Stern (back)

Freeboard(distance from waterline

to top edge of hull)

Draft(distance from waterline

to bottom of hull)

Transom(structural piece that

forms the stern)

Figure 1 – A simple boat hull

Boat Hull Design Kit User Guide 57911 V0311 3

The Boat Hull Design Kit (Figure 2) contains the following items, which are needed to construct the foam prototype and the final wooden hull:

• Structuralfoam,1-15/16"x3-1/2"x12"• Pineblock,1-13/16"x3-1/2"x12"• 2screweyes(bowhookonwoodenhull)• 2drywallscrews• 3sheetsofsandpaper,differentgrades• Sheetof11"x17"graphpaper• Woodcarvingblock

The following items are needed for the design process and construction of the foam prototype and wooden boat hull:

• Ruler• Pencil• Scissors• Transparenttape• CopingsaworFreeHandFoamCutter

(Pitsco#54527)• Sandingsealer• Enamel-basedpaintorvarnish• Paintbrushes• Paperclip(forthebowhookonthefoamhull)• Adhesivespray(optional)

To construct the wooden boat hull, the following tools, which are available in the Boat Hull Design ToolSet(Pitsco#56813),areneeded:

• Woodrasp• Half-roundwoodfile• Copingsaw• Indexcard• Frenchcurvescraper• Setoffourrifflers

Materials Included

Items Required (not included)Ifavailable,thesepowertoolswillmaketheconstruction process easier and more precise:

• Bandsaw• Drillwith1/16"drillbit• Belt/discsander(forroughshaping)• Dremeltoolorotherhobbytoolwith

accessories (for intricate polishing and shaping)

• Carvingtoolset• Vise

Figure 2 – The Boat Hull Design Kit


Before cutting that block of wood, you need to do alotofplanning.Infact,theplanningprocesswillprobably take longer than the actual construction of the hull. The reason is very simple: Before constructing the boat, you need to be sure you have designed the very best boat hull that you can.

After designing the hull, you will make a foam prototype to learn the design and construction process, test the prototype in the AquaTrak to get all the bugs out of the design, and then carve a

wooden boat for competition. Most importantly, keep improving your design until you have carefully crafted an outrageously creative boat that makes you proud!

The flowchart below outlines the process to follow as you design, build, and test the boat hull. The process is similar to that used by professional boat designers.

The Hull Design Flowchart

Figure 3 – The hull design process

Concept sketches

(pg 8)

Three-view plan

(pg 7)

Lofting(pg 11)

Foam prototype

(pg 12)

Testing (pg 13)

Testing (pg 13)

Wooden boatproduction

(pg 14)

Testing (pg 13)

Finishing(pg 15)

Prep for competition

(pg 20)

Testing the hull design: If you are not satisfied with the results at any step, go back to a previous step. How far back you go depends on the test results and on how much you need to change the design to get the boat the way you want it.

Unsatisfactory Results

Competition!


SpecificationsWhen designing your boat hull, you follow a set of designrules,orspecifications.Somespecificationsmight be set by your teacher or by the rules of a competition you are entering. Before beginning the design process, learn what specifications you must meet.

Intended FunctionsNext, consider the intended function(s) of the hull. For the AquaTrak curriculum activity, “Over the Long Haul,” you need to design a freighter that can carry a large load of cargo and still move with enough speed and efficiency to make a profit. For “The Great Boat Race,” the drag boat will be designed primarily for speed. You decide what specifications are necessary to meet these (or other) performance requirements.

Size and ShapeYou control the size (length and width) and shape (bow,stern,andbottom)ofthehull.Figure4illustrates the symmetry of a boat hull (both sides have the same shape), and defines two important measurements: length overall (LOA) and beam (width).

The hull should always be symmetrical, but LOAandbeammayvaryconsiderably.Ifyou’redesigning a hull for speed, would you want a long, narrow hull or a short, wide one? Would this differ ifdesigningforload-bearingcapacity?How?

Important Factors in Hull DesignHydrodynamicsHydrodynamics is the science of fluid behavior and movement. The smooth movement of water past the hullgreatlyimprovestheboat’sperformance.Thismovement, in turn, is affected by the shape of the hull – including bow, stern, and bottom shapes.

The simplest hydrodynamic hull shape is a pointed bow and a rounded stern. What do you think the water movement around such a shape would be? What variations in these shapes would improve performance? How would each of the bottom typesinFigure5onthenextpageaffecttheboat’shydrodynamics?

Displacement The weight of water that the boat moves, or displaces, as it settles into the water is called displacement.Displacementisequaltotheboat’sweight.

Hulls can be divided into two general categories: displacement hulls and planing hulls. Displacement hulls push the water aside as they move through it; planing hulls move over the bow wave on the surface of the water. Displacement hulls can have anyofthebottomshapesshowninFigure5onthenextpage.Ifthereisenoughpowerpushingtheboat,allexcepttheround-bottomtypecanplaneaswell.

Figure 4 – Top view of hull showing basic dimensions and directions

Beam (width)

Port (left) side

Length Overall (LOA)

Centerline

Starboard (right) side


Ifdesigningahullforspeed,wouldyouwantalarge or a small displacement? Would you want the displacement to be smaller or larger if you are planning to carry cargo?

StabilityEvery boat must be stable enough to not capsize under ordinary (or even extraordinary) circumstances. What combination of size and shape (long and narrow, short and wide) will make the hull most stable?

How will designing the boat for stability affect its performance in other areas (such as hydrodynamics, speed,orload-carryingcapacity)?

Remember, no design can do everything. Your job as a designer is to determine what the boat must be able to do, and find the combination of design factors that will best meet those needs. As with everythingelseinlife,therewillbetrade-offs–forexample, a faster boat will hold less cargo and vice versa.

Don’tbeafraidtokeeptryingnewdesigns.Soonerorlater,youwillfindonethat’sjustright.Formoreinformationondesigncriteria,tryPitsco’scurriculum guide, Boat Design and Testing: From AquaTrak to the Oceans or any of the boat design bookslistedinthecurriculum’sreferencesection.

Figure 5 – Common hull bottom shapes

A. Flat Bottom

B. V-Bottom

D. Multichine Bottom

E. Planing Hull (one of many)

C. Round Bottom F. Multihill (catamaran)


Boat Hull Shapes

Figure 6 – Variations in boat hull shapes


Use this page to make some rough concept sketches forthehulldesign.Don’tworryaboutdimensionsor scale at this point. Just think about how you want the boat to look.

As you design keep in mind the specifications, boat’sintendedfunction(s),anddesignfactorslistedonpages5and6.Youmightwanttodraweachdesign from more than one angle – the front and side views, for example.

Concept SketchesWhat design features will make the boat fast? Or able to carry a lot of cargo? How will it perform hydrodynamically?Canyoumakeitwiththetoolsand materials that are already available?

Keep trying designs until you find one that seems to meet all the criteria. Most of all, be creative! Let your imagination run wild!


What is a Three-View Plan?The next step is to choose your best design and drawathree-viewplanofit,liketheoneinFigure7below.Thisplanshouldhaveascaleof1/2"=1";that is, it will be half the size of the final boat hull youmake.Youcansketchyourthree-viewplanintheblanksonpage10.

ViewAiscalledtheprofileview.Itrepresentstheside view of the hull.

ViewBiscalledthebreadthview.Boatdesignersusually draw only half the breadth (width), because boats are symmetrical. However, you may want to

draw both sides of the hull to better visualize how it will look.

ViewC,calledthebodyplanview,representstwoend views (cross sections) through the hull. The left half represents the end view from a section made through the end of the boat near the stern. The right half represents the end view from another section madenearthebow.Ifthebowandsternarethesame in your design, these two sections will also be on either end, several lines may be drawn on each section to indicate the change.

Load Waterline Length (LWL)(length of hull at waterline)

Waterline(line where hull floats)

Freeboard(distance from waterline to top edge of hull)

Draft(distance from waterline to bottom of hull)

a b

Beam(width)

Centerline

Length Overall (LOA)

a b

LWLLeft: Section A on Profile View (stern)Right: Section B on Profile View (bow)

Figure 7 – Sample three-view plan

B. Breadth (top) View

A. Profile (side) View

C. Body Plan (cross sectional) View


B. Breadth (or Half-Breadth) View

Making Your Three-View Plan

A. Profile View

C. Body Plan View

Figure 8 – Blanks for three-view plan


Transfer the TemplatesNow, you are ready to transfer the paper templates to the foam block.

Using scissors, carefully cut out the profile plan and attach it to the side of the foam block with transparent tape. Trace around the profile plan with a pencil.

Note:Ifusinghandtoolstoshapetheprototype,consider tracing the profile on both sides of the block.

Next, cut out the box for the breadth plan, fold it inhalf,andcarefullycutaroundthehalf-breadthdrawing (Figure 9). Unfold the paper, tape it to the top of the foam block, and trace the outline onto the foam.

Repeattheprocesswiththebodyplans.Cutoutthe box (or boxes), fold in half, and cut out the pattern(s) to make full end views. Trace these onto the ends of the foam block.

You are now ready to shape the foam prototypes!

LoftingLofting is the process of making patterns or templatesfromthedesigner’sdrawings.Makethepatterntofullscaleusingthepieceof11"x17"graph paper in the Boat Hull Design Kit.

Take MeasurementsMeasure the foam block and draw boxes to full scale for the breadth and profile plans.

Work carefully and make your measurements as exact as possible because the graph paper templates will be cut out and traced onto the foam block to make the prototype. As you make the drawings, refer to the specifications to be sure your design meets all of them.

Draw the PlansFirst, draw the profile plan in the appropriate box.

Next, draw a line down the center of the box for the breadthplan.Inonehalfofthebox,drawthehead-breadth plan. Later, when you cut out the box, fold it in half and cut around the drawing. This will form asymmetricalfull-breadthpatternthatcanbetracedonto the top of the foam block.

Ifthebowandsternaredifferentshapes,youneedto draw two boxes for the body plan. Draw half of the bow in one box and half of the stern in the other box. Fold the boxes and cut out the patterns; you will have full end views of both bow and stern.

Duplicate the DrawingsAfter completing the lofting process, make several copies of the drawings. You need two to serve as templates for building the foam prototype and wooden hull and one to turn in your teacher (if required).

Note:Ifyoumakeextensivedesignchanges,youneed to repeat the lofting process before building the wooden boat.

Figure 9 – Cutting the folded half-breadth plan


3.Turntheblockuprightandcutoutthebreadthviewofthedesign(Figure11).

4. Again,putthepiecestogetherwithmaskingtape, and cut the end pieces (body plan) according to the design.

5. Removethewastepiecesandmaskingtapefrom the block and discard them.

6. Hollowouttheinsideofthehulltoformaseat,or hold, if this is part of the design.

7. Sandtheprototypeuntilitisverysmooth.Asmooth surface minimizes drag on a hull as it flows through the water.

8. IfyourclassroomhasaPitscoFLOVisualizationTunnel (or a similar small wind tunnel), use it to observe the airflow patterns around the boat hull. As air flows over the hull, turbulence will indicate where the hull is not smooth and where design problems exist. Modify the shape of the hull to minimize the turbulence.

9. Ifyoudonothaveaccesstoawindtunnel,study the foam prototype and try to identify any potentialdesignproblems.Carveandsandyourprototype until satisfied that the design meets specifications and will perform well when tested in the AquaTrak.

Caution: Before using any tools, first check with your instructor for proper operating procedures and important safety information. Misuse of power or hand tools could result in serious injury.

The foam block with the template lines traced on it shouldlooklikeFigure10.

To cut out the foam prototype, you need a coping saw,FreeHandFoamCutter*,orothertoolsprovidedbyyourinstructor.Cutcarefullyalongthetemplate lines you traced earlier as follows:1.Turntheblockonitssideandcuttheprofileline

all the way through.2. Gather all the pieces and put them back

together with masking tape.

Shaping the Foam Prototype

* TheFreeHandFoamCutter(Pitsco#54527)canbeusedtoroughoutshapetheprototype.Thehotwirecutsthrough foam quickly and quietly with no mess. Using the cutting wire in the vertical position is similar to using a band saw.

Figure 11 – Using a coping saw to cut the foam prototype

Figure 10 – Foam block with template lines drawn


Testing and Modifying the PrototypeThe moment has arrived – it is time to put your boat in the water!

The general procedure is as follows:

1. Checktheboathullagainstthespecificationsto be certain it meets size, weight, and other requirements.

2. Fashion a boat hook from a paper clip, and insert the hook into the center of the bow.

3. AttachtheloopontheAquaTrak’spulleylinetothehookonthehull.Checkthepulleyweights(thepowerfortheboat’smovement)andbesurethe power is low for the first set of tests.

4. RunapreliminarytestoftheboathullintheAquaTrak, observing the motion of the hull and the waves it generates.

5. Foraccuratetestsofthefoamprototype,itsdisplacement must be as close as possible to the displacement of the finished wooden hull. To simulate this condition, load the foam hull with cargountilthewaterlineisaboutone-thirdofthe way up the side of the hull.

6.Testanyoftheperformancefactors(nextcolumn) that are relevant to the design. Record and graph the results on the “Foam Prototype HullDataSheet”(pages16and17),ormakeyour own tables and graphs. Make other tests on your own or as directed by your instructor.

7. Basedontheresultsofthesetests,makeanydesign changes that you think would improve performance and test the hull again. (You may go through this process several times until satisfied with the design.)

Performance Factors:• Hydrodyanics. As the boat hull travels through

the AquaTrak, is the water flow around it smooth and straight or rough and choppy? A smooth, straight flow indicates lower drag on the hull and thus greater speed. How can you change the design to decrease drag?

• Speed. Measure the time it takes the hull to travel several different distances along the AquaTrak. Record the results in Table A, and graphtheminFigureA(page16).Calculatehullspeed as distance traveled (cm) divided by time (sec),orS=D/T.Whatdesignchangesmightincrease speed?

• Power. Measure the time it takes the hull to travelthelengthoftheAquaTrak*usingseveraldifferent pulley weights (powers). Record the results in Table B, and graph them in Figure B (page16).Figurespeedateachpower.Howdoes it change? Make a graph showing this change.

• Load. Measure the time it takes the hull to travelthelengthoftheAquaTrak*usingseveraldifferent loads (brass weights braced in the hold).InTableConpage17,recordthechanges in speed, draft, and freeboard as you change the load. Then, graph the changes in FiguresC,D,andEonpage17.Howdoeschanging the load affect these factors? How does it affect stability? How can you modify the hull to carry a heavier load?

After deciding on design changes, modify the hullwithcarvingtoolsand/orsandpaper.Ifthechanges are extensive, you need to repeat the lofting process to make another template.

* Toobtainthecorrectdistancepertrial,substractthedistancebeforethestartinglineplusthedistanceafterthefinishlinefrom600cm(thetotallengthoftheAquaTrak).


Shaping the Wooden HullNow that the foam prototype has been designed, tested, and modified to your satisfaction, you are ready to form a final wooden hull.

1. Modifyacopyoftheoriginaltemplatessothatthey conform to the final shape of your foam hull.(Ifyoumadeextensivemodifications,youwill need to obtain a new piece of graph paper and make a new set of templates.)

2. Cutoutthetemplates,attachthemwithtapetothe wooden block, and trace around them with a pencil. (Alternatively, attach the templates to thewoodenblockwithadhesivespray.Sawtheblock[Step4]withthetemplateattached.)

3. Toavoiddamagewhencarvingthehull,usethe drywall screws provided to attach the small carving block to the deck side of the wooden hull block. Place the carving block in a vise with the hull bottom of the wooden block facing up.

Caution: To avoid injury, use extreme care when operating either hand or power tools. Use toolsonlyunderyourinstructor’ssupervision.

4. Carefullycutouttheprofileofthehull,usingthecopingsaw(Figure12)intheBoatHullDesignerToolSetorabandsawprovidedbyyourinstructor.Cutontheoutsideofthetemplate lines, to avoid cutting away too much material.• Cuttheprofilelinefirst.• Tapethepiecesbacktogethertoformtheir

original shape, and cut the top (breadth) view.

• Cutanyremainingendpiecestorevealthebody plan (bow and stern) shapes.

5. Withyourinstructors’help,cutouttheseatorhold area using the tools provided.

6. Smooththebodyshape,usingawoodrasp,rifflers,andcoursesandpaper.Ifusingabeltsander, gently touch the hull to the sander belt. Becareful–it’seasytopresstoohardandaccidentally remove too much material.

7. Usefinesandpapertoobtainaverysmoothsurface. There should be no humps or dips along the sides or bottom of the hull. Boatbuilders call this a fair hull.

8. Installthebowhookonthefrontofthehull:a. Determine where to install the hook by

marking the spot on the bow where the pulley line, when inserted into the hook, will be parallel to the water.

b. Usingadrillwitha1/16"drillbit,drillahole1/8"deepinthehull.

c. Using pliers, open the screw eye to form a hook.

d. Insertthescreweye.Loopthepulleylinefrom the AquaTrak over the hook.

9. The hull is now ready to be tested in the AquaTrak. Repeat the tests that you did on the foam prototype and note the results on the “FinalWoodenHullDataSheet”(pages18and19).Howdotheresultscomparewiththatofthe foam prototype? What do you think is the cause of any differences observed?

10.Makeanyminordesignchanges(suchassmoothing or sanding) that you think will improve performance.

Figure 12 – Using a coping saw to cut the foam prototype


Finishing the Wooden HullAt this point, your boat hull should be tested and modifiedtoyoursatisfaction.It’stimetofinishitbyaddingseveralcoatsofenamel-basedpaintorvarnish. Really let your imagination go and make the hull truly yours in both color and exterior design.Here’stheprocess:

1. Removethebowhookuntilyouhavecompletedthe finishing process.

2. Make sure the hull is sanded as smooth as you can get it. Often, the amount of time spent sanding determines the quality of the paint job. First,sandwithmedium-gritsandpaper.Takeyour time and remove all imperfections. For an extremely smooth surface, apply a coat of sanding sealer before final sanding.

3. Brushorsprayontothehullathincoatofpaintorexterior-gradevarnish.Afterthehulldries,lightly sand it with fine sandpaper.

4. RepeatStep3severaltimes,untilthehull’sfinish is very smooth. All wood on a boat that is varnished is called finished bright. Why do you think such a finish is important on a boat hull?

5. Afterthefinalcoatofpainthasdried,youcanbrush on fine detail work, such as pinstripes or lettering.

6. Considerthatwhenyoumeasurehullmassordisplacement,thecoatsofpaintand/orvarnishapplied during finishing will add several grams to the weight of the hull. Reweigh the finished hull, making sure it still meets specifications, and adjust the value for hull mass on the “Final WoodenHullDataSheet”(page18).

Figure 13 – Painting a wooden hull


Foam Prototype Hull Data Sheet, Part 1

Name: ______________________________________ Date: ________________

Specifications

LOA:_____________ Draft: _____________

LWL: _____________ Freeboard: _____________

Beam: _____________ Displacement: _____________

Wetter surface area: _____________ Hull mass (empty): _____________

Theoreticalhullspeed*:_____________m/sec_____________mph_____________knots

*1.34x (LWL)

Performance

TableA:Speedatagivenpower TableB:Effectofpoweronspeed (distance/timerelationship) (power/timerelationship)

Power: _____________

Power Time1 meter2 meters3 meters4 meter5 meters

Power Time

16

14

12

10

8

6

4

2

1 2 3 4 5

Tim

e (s

ec)

16

14

12

10

8

6

4

2

1 2 3 4 5

Tim

e (s

ec)

Distance (meters) Power (grams)

Figure A Figure B


Foam Prototype Hull Data Sheet, Part 2

16

14

12

10

8

6

4

2

1 2 3 4 5

Free

boar

d (m

m)

Load

Figure E: Effect of Load on Freeboard

16

14

12

10

8

6

4

2

1 2 3 4 5

Tim

e (s

ec)

Load

Figure C: Effect of Load on Time

40

35

30

25

20

15

10

5

1 2 3 4 5

Dra

ft (m

m)

Load

Figure D: Effect of Load on Draft

Name: ______________________________________ Date: ________________

Performance continued

TableC:Effectofloadonspeed Distance:LengthoftheAquaTrak*

Load Time Draft Freeboard1. _________ _________ _________ _________

2. _________ _________ _________ _________

3. _________ _________ _________ _________

4. _________ _________ _________ _________

5. _________ _________ _________ _________

*To obtain the correct distance for each trial, subtract the distance before the starting line plus the distance after the finish line from 600 cm (the total length of the AquaTrak).


Final Wooden Hull Data Sheet, Part 1Name: ______________________________________ Date: ________________

Specifications

LOA:_____________ Draft: _____________

LWL: _____________ Freeboard: _____________

Beam: _____________ Displacement: _____________

Wetter surface area: _____________ Hull mass (empty): _____________

Theoreticalhullspeed*:_____________m/sec_____________mph_____________knots

*1.34x (LWL)

Performance

TableA:Speedatagivenpower TableB:Effectofpoweronspeed (distance/timerelationship) (power/timerelationship)

Power: _____________

Power Time1 meter2 meters3 meters4 meter5 meters

Power Time

16

14

12

10

8

6

4

2

1 2 3 4 5

Tim

e (s

ec)

16

14

12

10

8

6

4

2

1 2 3 4 5

Tim

e (s

ec)

Distance (meters) Power (grams)

Figure A Figure B


Final Wooden Hull Data Sheet, Part 2

16

14

12

10

8

6

4

2

1 2 3 4 5

Free

boar

d (m

m)

Load

Figure E: Effect of Load on Freeboard

16

14

12

10

8

6

4

2

1 2 3 4 5

Tim

e (s

ec)

Load

Figure C: Effect of Load on Time

40

35

30

25

20

15

10

5

1 2 3 4 5

Dra

ft (m

m)

Load

Figure D: Effect of Load on Draft

Name: ______________________________________ Date: ________________

Performance continued

TableC:Effectofloadonspeed Distance:LengthoftheAquaTrak*

Load Time Draft Freeboard1. _________ _________ _________ _________

2. _________ _________ _________ _________

3. _________ _________ _________ _________

4. _________ _________ _________ _________

5. _________ _________ _________ _________

*To obtain the correct distance for each trial, subtract the distance before the starting line plus the distance after the finish line from 600 cm (the total length of the AquaTrak).


Preparing for CompetitionCongratulations–youdesignedandbuiltyourownboat hull! You followed the design process from concept through building, testing, and finishing. You met the assigned specifications. Your boat hull is the very best you can make it.

Nowitistimetotesttheboat’sperformanceintheAquaTrak against boats built by your classmates. Whether trying to win the speed trials in “The Great

Boat Race,” make the most profit as a freighter captain in “Over the Long Haul,” or vying for a completely different kind of trophy – perhaps the mostcreativedesign–you’reawinnerifyou’velearned from the design and construction process and built a boat that makes you proud.

So,allboatsintothewater!

“The best way to begin a study of hull shapes is by examining midship sections. The midship section of a boat is a slice taken athwartship right through the hull, halfway between the bow and stern. The shape of the midship section tells us the basic form of the hull – flat bottom,Vbottom,orroundbottom.Astudyofthemidship-sectionshapecantellusmuchmore,though,such as whether the boat is tender or stable, hard riding or with an easy motion, even fast or slow . . . .

“Theflat-bottomboatisanidealtypeforthebeginningamateur building because it is the simplest to build, goes together quickly, and requires fewer tools and usuallylessmoneythanmorecomplexshapes.Flat-bottom boats have a deserved reputation for pounding in head seas, but intelligent design can reduce this substantially provided the vessel is used as intended . . . .

“WhenwespeakofV-bottomboats,mostpeoplethinkofahigh-speedmotorboat.Thecharacteristicsofsucha hull . . . are a fairly high chine line forward that submerges just forward of midships and continues aft almost parallel to the LWL. The stern is wide to enable the vessel to get up onto a plane . . . .

“Ingeneral,theround-bilgehullissuperiortotheflatsorV-bottomhullforoff-shoreandrough-waterusage.Itisstrongerandhasaslowerrollwithlesssnapthana chine hull of the same general size. For sailing yachts orsemi-displacementpowerboats,theshapereduceswetted surface and eliminates turbulence along the chines, cutting drag and increasing performance.”

– from Ted Brewer, Understanding Boat Design, 4th edition, pages 9, 11, 12, and 15. (Pitsco #52149)

“Ifyouplantotank-testyourmodel,usethe3/4"=1’scale.Atthisscale,themodel’stowingspeedwillbeexactly25percentofthefull-sizeboat’spotentialspeed.WhenItowatestmodel,Iweightthemodeldown to the desired waterline. Pulling it behind a skiff at,say,4mph,Iuseavideocameratorecordthemodel’sresponse,therebyapproximatingthedesign’sfull-sizeperformanceat16mph.Later,watchingthevideoandfreezingframe,Icananalyzethebowwaveand the wake action; sometimes even the effectiveness of the spray rail or trim tabs can be noted . . . .

“Inthe3/4-inch-scalemodel,theweightofthemodelisrelatedtothefull-sizeboatbythecubeofthelinearratio...Ifthelinearratiois16:1,a1-poundmodel’sweightcanbeprojectedto4,096poundsforthefull-sizeboat.Forballastweight,acopperpennyin3/4-inchscaletranslatestoaroughlyfull-sizeweightof25pounds.Itcanbegreatfuntocheckouttheweightsof engines, fuel tanks, and everything else that might affect the centers of balance and gravity in the boat.

“Building a flotation model is most easily done by followingthehalf-modelbuildingprocedureandsimply gluing lifts and planking up both sides of the boat’sprofile...youcanbuildyourflotationinscaleasyouwouldafull-scaleversion–simplycuttingoutthepanelsoftheboatandusingnylon-filamentpacking tape . . . instead of wires to stitch the boat. Five-minuteepoxyorCAgluecanbeusedinlieuofepoxyandglassjointsasinthefull-sizedboat.. . This is probably the greatest benefit of the whole modeling exercise – it gives you a scale glimpse into the building process.”

– from Samual Devlin, Devlin’s Boatbuilding, pages 68-69, International Marine, Camden, ME., 1996.

P.O. Box 1708 • Pittsburg, KS 66762shop.pitsco.com

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