4.1 General arrangement plan

8/[

4.3 Shell expansion

4.4 Other plans

5 Important data on various ships

SHIP KNOWLEDGE

A MOD ER N ENC Y CLO P EDIA

1. Principal Dimensions

1.1 General

Shipwise

The Shape OF A Ship

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All aspects concerning the measurements of seagoing vessels are arranged in the certificate of registry act of 1982. Part of the certificate of registry act is the International treaty on the measurement of ships, as set up by the IMO- conference in 1969. The treaty applies to seagoing vessels with a minimum length of 24 metres and came into force in July1994.

Explanation of the picture at the right:

—

S

= Summer ( for water with a density of 1.025 t/m³)

W Winter( ditto)

T Tropics ( ditto)

WNA Winter North

Atlantic ( ditto)

TF Tropical Fresh water

F Fresh water

When a ship carries a deck cargo of timber, and certain demands are met, this ship is allowed to have more draught ( less freeboard). This is because of the reserve buoyancy caused by the deck cargo. To indicate this, the ship has a special Plimsoll’ s mark for when it is carrying a deck cargo of timber, the so-called timber mark.

1.2 Dimensions

Length between perpendiculars ( Lpp) Distance between the Fore and the Aft Perpendicular.

Length over all ( Loa)

The horizontal distance from stem to stern.

Length on the water line ( Lwl)

Horizontal distance between the moulded sides of stem and stern when the ship is on her summer mark.

Breadth(B)

The greatest moulded breadth, measured from side to side outside the frames, but inside the shell plating.

Breadth over all

The maximum breadth of the ship as measured from the outer hull on starboard to the outer hull on port side.

Draught at the stem ( Tfwd)

Vertical distance between the water line and the underside of the keel, as measured on the fore perpendicular.

Draught at the stern ( Ta)

The vertical distance between the water line and the underside of the keel as measured from the aft perpendicular.

Trim

The difference between the draught at the stem and the draught at the stern.

The breadth / depth-ratio; varies between 1.3 and 2. If this value becomes larger, it will have an unfavourable effect on the stability ( because the deck will be flooded when the vessel has an inclination) and on the strength.

( mostly containers) can be placed on deck. It is typical for small container ships to use this strategy. As a consequence of this, dangerous situations can occur because the loss of reserve buoyancy can result in a loss of stability and more“water on deck”.

The NT may not be less than 30% of the GT.

Displacement ( in m³)

The displacement equals the volume of the part of the ship below the water line including the shell plating, propeller and rudder.

1.4 Volumes and weights

Nett Tonnage Underwater body ( in m³)

General

The dimensions of a ship can be expressed by using termsm which describe the characteristics of the ship. Each term has a specific abbreviation. The type of ship determines the term to be used. For instance, the size of a container vessel is expressed in the number of containers it can transport; a roll-on roll-off carrier's size is given by the total deck-area in square metres and a passenger ship in the number of people it can carry. At the IMO- conference in 1969 the new units “Gross Tonnage” and “Nett Tonnage” were introduced, to establish a world-wide standard in calculating the size of a ship. In many countries the Gross Tonnage is used to determine port dues and pilotage, or to determine the number of people in the crew.

Register ton

To determine the volume of a space the register ton is used. One register ton equals 100 cft, or 2.83 m³.

Gross Tonnage

The gross tonnage is calculated using a formula that takes into account the ship’ s volume in cubic metre below the main deck and the enclosed spaces above the main deck.

This volume is then multiplied by a constant, which results in a dimen- sionless number ( this means no values of T or m³ should be placed after the number). All distances used in the calculation are moulded dimensions.

In order to minimize the daily expenses of a ship, the ship owner will keep the GT as low as possible. One way of doing this is by keeping the depth small, so more cargo

The Nett Tonnage is also a dimensionless number that describes the volume of the cargo space. The NT can be calculated from the GT by subtracting the volume of space occupied by:

- crew

The underwater body of a ship equals the displacement minus the contri- bution of the shell, propeller and rudder. Or: the calculated volume of the part of the hull which is sub- merged in the water, on the outside of the frames without extensions.

- navigation equipment

- propulsion equipment

- workshops

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Displacement (t) = waterdisplacement (m³) * density of water (t/m³)

Light displacement ( in t)

This is the weight of the hull including the regular inventory. The regular inventory includes: anchors, life-saving appliances, lubricating oil, paint, etc.

Dead weight ( in t)

This is the weight a ship can load until the maximum allowable submersion is reached. This is a constant, which is unique for every ship.

Dead weight (t) = maximum weight Δ(t) - light displacement (t)

Dead weight (t) = maximum weight Δ(t) - actual weight Δ(t)

Cargo, carrying or dead weight capacity ( in t)

This is the total weight of cargo a ship can carry. The cargo capacity ( in t) is not a fixed number, it depends on the ship's maximum allowable submersion, which will include the capacity ( in t) of fuel, provisions and drinking water. For a long voyage there has to be room for extra fuel, which reduces the cargo capacity. If, on the other hand, the ship refuels ( bunkers) halfway, the cargo capacity is larger upon departure. The choices for the amount of fuel on board and the location for refuelling depend on many factors, but in the end the master has final responsibility for the choices made.

Cargo capacity (t) = dead weight (t) - ballast, fuel, provisions (t).

The cargo capacity largely determines the amount of money a ship generates.

2. Form coefficients

Form coefficients give clues about the characteristics of the vessel’ s shape from the water line down into the water. This makes it possible to get an impression of the shape of the underwater body of a ship without extensive use of any data. However, the form coefficients do not contain any information on the dimensions of the ship, they are non-dimensional numbers.

2.1 Waterplane-coefficient Cw.

The waterplane-coefficient gives the ratio of the area of the water line A and the rectangular plane spanned by Lpp and Bmld. A large waterplane-coefficient in combination with a small block-coefficient ( or coef- ficient of fineness) is favourable for the stability in both athwart and fore and aft direction.

2.2 Midship section coefficient, Cm.

The midship-coefficient gives the ratio of the area of the midship section ( Am) and the area spanned by Bmld and T.

2.3 Block coefficient, coefficient of fineness, Cb.

The block coefficient gives the ratio of the volume of the underwater body and the rectangular beam spanned by Lpp, Bmld and T. A vessel with a small block coefficient is referred to as‘slim’. In general, fast ships have a small block coefficient.

Customary values for the block coefficient of several types of vessels:

Tanker 0.80-0.90

Freighter 0.70-0.80

Container vessel 0.60-0.75

Reefer 0.55-0.70

Frigate 0.50-0.55

V

Block coefficient ( Cb) = Lpp x Bmld x T

A ship with a small block-coefficient and a large midship section coefficient

Graphical representation of the block coefficient.

A ship with a large block-coefficient and a large midship section and prismatic coefficient.

Prismatic coefficient( Cp)=

2.4 Prismatic coefficient, Cp.

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. The Cp is important for the resistance and hence for the necessary power of propulsion ( if the Cp decreases, the necessary propulsion power also becomes smaller).

The maximum value of all these coefficients is reached in case of a rectangular beam, and equals 1. The minimal value is theoretically 0.

3. Lines and offsets ( Lines plan)

When the principal dimensions, displacement and line-coefficients are known, one has an impressive amount of design information, but not yet a clear image of the exact geometrical shape of the ship. This can be obtained by the use of a lines plan.

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

water lines

Water lines.

Horizontal cross-sections of the hull are called water lines. One of these is the water lines/ design draught. This is the water line used in the design of the ship when it is hypothetically loaded. When the water lines are projected and drawn into one particular view, the result is called a water line model.

The waterlines

Ordinates. Evenly spaced vertical cross-sections in athwart direction are called ordinates. Usually the ship is divided into 20 ordinates, from the centre of the rudder stock ( ordinate 0) to the intersection of the water line and the mould-side of the stem ( ordinate 20). The boundaries of these distances are numbered 1 to 20, called the ordinate numbers. A projection of all ordinates into one view is called a body plan.

The ordinates

Buttocks

Vertical cross-sections in fore and aft direction are called buttock lines. These cross-sections are parallel to the plane of symmetry of the ship. When the buttocks are projected and drawn into one particular view, the result is called a sheer plan.

Buttock lines

The diagonals are cross-sections of fore and aft planes that intersect with the water lines and verticals at a certain angle. On the longitudinal plan they show up as straight lines. The curvature of the water lines and buttocks are compared to each other and modified until they are consistent. When this procedure is executed, the results can be checked using the diagonals. The most common diagonal is called the bilge diagonal.

The diagonals

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Nowadays the lines plans are being made with the aid of computer- programs that have the possibility to transform the shape of the vessel automatically when modifications in the ship's design require this. When the linesplan is ready, the programs may be used to calculate, among other things, the volume and stability of the ship.

As shown in the lines plan below, both the water lines and the buttocks are drawn in one half of the ship. In the body plan, the frames aft of the midships are drawn on the left side and the fore frames are drawn on the right. The linesplan is drawn on the inside of the skin plating.

The lines plans shown here are of vessels that have underwater bodies

that differ quite dramatically. The reader can tell from these plans that a ship will be slimmer with smaller coefficients, when the water lines, ordinates and l buttocks are more

closely spaced. For instance, a rectangular forecastle has only one water line, one ordinate and one buttock, the coefficients are 1.

Length over and :212,000 [m]

Moulded breadth :32.240 [m]

5 Draft :12.240 [m] 5

Displacement :59279 [t]

Cb :0.691 [-]

Cp :0.707 [-]

Cm :0.978[-]

LCB :-0,343 [% Lpp]

Xb :102,561 [m]

4| KMtransverse : 14.430 [m]

4

1 Linesplan

Trawler harm Printed: 29-8-2002

A B C D E F G

Last modification: 29-8-200210:59:39 Scale: Fitted

Lpp =35.000m

Cb =0.565

Cm = 0.908

LCB =2.90 %

Tmld =4.500 m

Cp =0.622

KM =5.13 m

Lpp = 23.500 m

Cb =0.157

Volume = 92 m³

Bmld = 6.250 m

Cm =0.305

LCB =-3.16 %

Tmld =4.000 m

Cp =0.515

KM = 6.06 m

Lpp = 73.200 m

Cb =0.637

Volume =4196 m³

Bmld = 18.000 m

Cm =0.933

LCB = - 0.75 %

Tmld =5.000 m

Cp =0.683

KM = 8.67 m

Lpp = 134.000 m

Cb = 0.710

Bmld = 28.000 m

Cm = 0.992

LCB = - 2.24 %

20.000 20.000

15.000 15.000

Tmld =7.000 m

Cp =0.715

10.000 10.000

5.000 5.000

KM = 14.46 m

0.000

0.000

Frigate

LCB =-2.30%

Tmld =3.250m

Cp =0.601

KM = 6.17 m Frigate

Lpp = length between perpen- diculars

Cm LCB

= midship section coefficient

Bmld = breadth moulded Cp = prismatic coefficient

Tmld = draught moulded

Volume = volume of the under-

Cb water body, as measured KM

block coefficient or coefficient of fineness

on the water lines, to the

= point of application of the= resultant of all upward forces; longitudinal centre of buoyancy(m).

= Height of meta-centre above the keel (m).

Of the many drawings, only the most important ones are mentioned here. In general, the following demands are made:

The general arrangement plan, safety plan, docking plan and capacity plan have to be submitted to the Shipping Inspectorate for approval.

The general arrangement plan, midship section drawing, shell expansion and construction plan ( or sheer plan or working drawing) have to be submitted to the classification bureau for approval.

4.1 General arrangement plan

The general plan roughly depicts the division and arrangement of the ship. The following views are displayed:

-a (SB) side-view of the ship.

- the plan views of the most important decks.

- sometimes cross-sections, or a front and back view are included.

The views and cross-sections mentioned above, display among other things:

- the division into the different compartments ( for example: tanks, engine room, holds)

- location of bulkheads.

- location and arrangement of the superstructures.

- parts of the equipment ( for example: winches, loading gear, bow thruster, lifeboat).

Next to these, some basic data are included in the drawing like: principal dimensions, volumes of the holds, tonnage, dead weight, engine power, speed and class.

Fig: General arrangement plan of a multi-purpose vessel that carries mainly paper, timber products and containers.

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SHEET:

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This cross-section shows one or more athwart cross-sections of the ship. In case of a freighter it is always a cross-section of the hold closest to the midship. Some of the data shows includes:

- principal dimensions

-engine power and speed

- data on classification

-equipment numbers

- maximum longitudinal bending moment.