2- Definitions, Principal Dimensions, Form Coefficients

Definition

1- Perpendiculars1- Perpendiculars

Imaginary lines perpendicular to the base line or plane (and the water line)

On the ship there is a :

- Forward Perpendicular - Forward Perpendicular (F(Fpppp or F or Fpp))

This is the line crosses the intersection of the water line and the front of the stem

-Aft Perpendicular -Aft Perpendicular (A(Apppp or A or App))

This line usually aligns the centre line of the rudder stock. This is the imaginary line around which the rudder rotates.

2. Waterlines2. Waterlines

The waterline of a ship lying in the water. There are different waterlines (i.e load-lines) for different loading conditions, such as:

- Light waterlineLight waterline

The waterline of a ship carrying only her regular inventory.

- Fully loaded waterlineFully loaded waterline

The waterline of maximum load draft in sea water.

- Construction (Scantling) waterline Construction (Scantling) waterline (C(CWLWL))

The waterline used as the limit to which the various structural components are designed.

3- Plimsoll Mark (freeboard mark)3- Plimsoll Mark (freeboard mark)

The freeboard mark is a symbol indicating the maximal immersion of the ship in the water, leaving a minimal freeboard for safety.

The mark consists of a circle with a diameter of 300 mm, through which a horizontal lines is drawn with its upper edge going through the centre of the circle.

This level indicates the minimal freeboard in salt water summer conditions. Beside this circle the loadline mark consists of a number of horizontal lines indicating the minimal freeboard required for other than summer conditions. All freeboard lines are 25 mm wide and are connected by a vertical line.

The freeboard mark is placed midships on each side of the ship.

The minimal operating freeboard depends on:

-Ship’s position at sea

-The time of year (summer, winter, etc,.._

4- Deck Line4- Deck Line

In general this is the extended line from the upper side of the freeboard deck at the ship’s side.

The deck line is placed above the Plimsoll mark so that the freeboard can be easily monitored by the ship’s crew or other interested parties

5- Permanent marks on the ship’s hull5- Permanent marks on the ship’s hull

It is very important the draft marks can be accurately read as easily as possible.

Dimensions

FP Forward Perpendicular

AP After Perpendicular

WL Waterline

WL WaterlineWL Waterline

CL CentrelineCL Centreline

11- Length over all LOA

It is the overall length of the vessel, i.e the horizontal distance over the extremities from stem to stern

22- Length between perpendicular LPP

It is the horizontal distance between the FP and AP

3- 3- Length waterline L LWLWL

Horizontal distance between the fore and aft when the ship is loaded at the summer mark, less the shell.

4- 4- Breadth over allBreadth over all B BOAOA

The maximum breadth of the ship as measured from the outer hull on the starboard to the outer hull on port side, including rubbing bars, permanent fenders.

4-4- Breadth or beam Breadth or beam BMLD

The greatest moulded breadth, measured from side to side at the outside of the frames, but inside the shell

55- Depth Depth D

The vertical distance between the base line and the upper continuous deck and is measured at the half Lpp at the side of the ship

66- Draft ForwardDraft Forward (TFWD)

Vertical distance between the waterline and the underside of the keel, as measured at the forward perpendicular

66- Draft at the sternDraft at the stern (TAF)

Vertical distance between the waterline and the underside of the keel, as measured at the after perpendicular

77- FreeboardFreeboard

The distance between the waterline and the top of the deck at the side ( at the deck line). The term summer freeboard means the distance from the top of the summer loadline and the upper edge of the deck line

88- Air draftAir draft

The vertical distance between the waterline and the highest point of the ship. The air draft is measured from the summer mark.

SheerSheer

This is the upward rise of the ship’s deck from mid length towards the bow and stern. The sheer gives the vessel extra buoyancy at the stem and stern

CamberCamber

The transverse curvature of the weather deck. The curvature helps to ensure sufficient drainage of any water on deck

40

Base lineBase line

Top of the flat keelplace

Keel (K)Keel (K)

Inter section of the base line and the center line plane

Beam: B Camber

Depth: D

Draft: T

FreeboardWL

KCL

FlareFlare

• FlareFlare : outward curvature of ship’s hull surface above the waterline

• Tumble HomeTumble Home : opposite of flare

Tumble HomeTumble Home

Positions of the shipPositions of the ship

ListList

Heeling to one side about the fore and aft axis

Heel to port side

Trim (t)Trim (t)

The difference between the draft at the stern and the draft at the stem i.e the trim fore (tF) + the trim aft (tA)

On an even keelOn an even keel, in proper trim

The draft of the stern equals the draft of the stem

Trim by head TF more than TA

Trim by stern TA more than TF

Volumes and weightsVolumes and weights

Register ton (RT)

To determine the size of a ship the RT is used. It is based on volume where one register ton equals 100 cubic feet or 2.83 m3

Gross Register TonnageGross Register Tonnage

The Gross Register Tonnage (GRT or GT) usually called Gross Tonnage, is calculated using a formula that takes into account the ship’s volume in cubic meters below the main deck and the enclosed spaces above the main deckNet Register TonnageNet Register Tonnage

The Net Register Tonnage is also a non-dimensional number that describes the volume of the cargo space. The NT is derived from the GT by subtracting the volume of space occupied by:

- crew

- Navigation equipment

-The propulsion equipment

- work stations

- Ballast

Volume of Displacement Volume of Displacement V mV m33

The displacement is the volume of the part of the ship below the waterline including the shell plating, propeller and rudder

Displacement Displacement ΔΔ ton ton

The displacement is the weight of the volume of water displaced by the ship

Lightship weight (ton)Lightship weight (ton)

This is the weight of the ship including the regular inventory but without any cargo, fuel or crew. The regular inventory includes: anchors. Life-saving equipment, lubricating oil, paint

Deadweight (ton)Deadweight (ton)

This is the weight of the a ship can take on until the maximal allowable immersion is reached. This is a fixed value, unique to each ship.

Cargo Capacity (t)Cargo Capacity (t)

This is the total weight of cargo a ship is designed to carry at a given time.

Hull Form CoefficientsHull Form Coefficients

Line coefficients define the characteristics of the vessel’s shape at and below the waterline. This makes it possible to get an impression of the shape of the underwater body of a ship without extensive use of any data.

1- Block Coefficient, Coefficient of fineness1- Block Coefficient, Coefficient of fineness C CBB

The block coefficient gives the ratio of the volume of the underwater body (V) and the rectangular block bounded by LPP, BMLD and draft (T). The vessel with a small block coefficient is reoffered to as fine.

2- Waterline coefficient CW

The waterline coefficient gives the ratio of the area of the waterline (Aw) and the rectangular plane bounded by LPP, BMLD.

Midship Section CoefficientMidship Section Coefficient C CMM

The midship (main frame) coefficient gives the ratio of the area of the midship section (AM) and the area bounded by BMLD and T.

Prismatic CoefficientPrismatic Coefficient C CPP

The prismatic Coefficient gives the ratio of the volume of the underwater body and the block formed by the area of the Midship Section AM and LPP.

When the principal dimensions, displacement and hull form coefficients are known, one has an impressive amount of design information, but not yet a clear image of the exact geometrical shape of the shape. The shape is given by the lines plane.

The shape of a ship can vary in height, length and breadth. In order to represent this complex shape on paper, transverse sections of the hull are combined with two longitudinal sets of parallel planes, each one perpendicular to the others

Since the ship is a 3-dimensional shape, data in x, y and z directions is necessary to represent the ship hull.

(Table of Offsets)Table of Offsets) Lines

- body plan (front View) - shear plan (side view) - half breadth plan (top view)

Example 1Example 1A ship has a length and breadth at the waterline of 40.1 m and 8.6 m respectively. If the water-plane area is 280 m2 calculate the coefficient of fineness of the water-plane area (CW).

SolutionSolution

Example 2Example 2A ship floats at a draught of 3.20 m and has a waterline length and breadth of 46.3 m and 15.5 m respectively. Calculate the block coefficient (CB) if its volume of displacement is 1800 m3.

SolutionSolution

Example 3Example 3A ship has length 200 m and breadth 18 m at the waterline. If the ship floats at an even keel draught of 7.56 m in water RD 1.012 and the block coefficient is 0.824 calculate the displacement.SolutionSolution

Example 4Example 4A ship floats at a draught of 4.40 m and has a waterline breadth of 12.70 m. Calculate the underwater transverse area of the midships section if CM is 0.922.

Example 5Example 5A ship has the following details: Draught 3.63 m; Waterline length 48.38 m; Waterline breadth 9.42 m;Cm 0.946; Cp 0.778.Calculate the volume of displacement.SolutionSolution

Tonnes per Centimetre immersion TPCTonnes per Centimetre immersion TPC

The TPC for any given draught is the weight that must be loaded or discharged to change the ship’s mean draught by one centimetre (1cm)

Where:

TPC : tonnes per cm

WPA : water plane area m2

ρ : water density 1.025 t/m3

Example 6Example 6Calculate the TPC for a ship with a water-plane area of 1500 m2 when it is floating in:(a) fresh water;(b) dock water of RD 1.005;(c) salt waterSolution:Solution:

LOAD/DISCHARGELOAD/DISCHARGE

Example 7Example 7M.V. Almar has a displacement of 13200 ton at an initial mean draught of 4.40 m in salt water and is required to complete loading with a draught of 6.70 m (displacement will reach 20610 ton). Calculate the amount of cargo that must be loaded.

Fresh Water Allowance (FWA)Fresh Water Allowance (FWA)Fresh Water Allowance (FWA) is the number of millimetres by which the mean draught changes when a ship passes from salt water to fresh water, or vice-versa, when the ship is loaded to the Summer displacement.The FWA is found by the formula:

TPCSW is the salt-water TPC value for the summer load draught.

Example 8Example 8A ship floats in SW at the Summer displacement of 1680 tonnes. If the TPCSW is 5.18, how much will the draught change by if the ship is towed to a berth where the density of the water is 1.000 t/m3?

3- Classification Societies & Governmental Authorities

Classification Societies

- Merchant shippers and underwriters provided ship lists and met Edward Lloyd 17th – 18th century

- Activities of classification societies (rules, certification, delegation by governments,…)

Governmental Authorities (IMO)

- 1959 (IMCO) inter governmental maritime consultative organization, 1982 IMO

- Committees (maritime safety committee MSC, marine environment protection committee MEPC)

-Conventions (SOLAS, MARPOL, ILLC, tonnage)

- Resolutions