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the length is not a fixed quantity for a particular ship, as it will depend upon the waterline at

Lwhich the ship is floating and upon the trim of the ship. This length is also shown in Figure 1 .

Breadth

The mid point of the length between perpendiculars is called ?amidships‘and the ship is usually broadest at this

point. The breadth is measured at this position and the breadth most commonly used is called the ?breadth

moulded‘. It may be defined simply as the distance from the inside of plating on one side to a similar point on the

other side measured at the broadest part of the ship.

As is the case in the length between perpendiculars, the breadth moulded dose not represent the greatest

breadth the breadth extreme is required (see Figure 2 ). In many ships the breadth extreme is the breadth moulded

plus the thickness of the shell plating where the strakes of shell plating were overlapped the breadth extreme was

equal to the breadth moulded plus four thicknesses of shell plating, but in the case of modern welded ships the

extra breadth consists of two thicknesses of shell plating only. The breadth extreme may be much greater than this in some ships, since it is the distance from the extreme

overhang on one side of the ship to a similar point on the other side. This distance would include the overhang of

decks, a feature which is sometimes found in passenger ships in order to provide additional deck area. It would be

measured over fenders, which are sometimes fitted to ships such as cross channel vessels which have to operate in

and out of port under their own power and have fenders provided to protect the sides of the ships when coming

alongside quays. Depth

The third principal dimension is depth, which varies along the length of the ship but is usually measured ant

amidships. This depth is known as the ?depth moulded and is measured from the underside of the plating of the

deck at side amidships to the base line. It is shown in Figure 2(a). It is sometimes quoted as a ?depth moulded to

upper deck‘ or ?depth moulded to second deck‘, etc. Where no deck is specified it can be taken the depth is

measured to the uppermost continuous deck. In some modern ships there is a rounded gunwale as shown in Figure

2(b). In such cases the depth moulded is measured from the intersection of the deck line continued with the

breadth moulded line. Other features

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The Naval Architect

The three principal dimensions give a general idea of the size of a ship but there are several other features which have to be considered and which could be different in two ships having the same length, breadth and depth.

The more important of these will now be defined. Sheer

Sheer is the height of the deck at side above a line drawn parallel to the base and tangent to the length of the ship and is usually greatest at the ends. In modern ships the deck line at side often has a variety of shapes: it may be flat with zero sheer over some distance on either side of amidships and then rise as a straight line towards the

ends; on the other hand there may be no sheer at all on the deck, which will then be parallel to the base over the

entire length. In older ships the deck at side line was parabolic in profile and the sheer was quoted as its value on + 20 ft the forward and after perpendiculars as shown in Figure 1. So called ?standard‘ sheer was given by the formulae: Sheer aft (in) = 0.1L+ 10 ft Sheer forward (in) = 0.2LThese two formulae in terms of metric units would give:

Sheer forward (cm) = 1.666L+ 50.8 m Sheer aft (cm) = 0.833L+ 25.4 m

It will be seen that the sheer forward is twice as much as the sheer aft in these standard formulae. It was often the case, however, that

considerable variation was made from these standard values. Sometimes the sheer forward was increased while the sheer after was reduced. Occasionally the lowest point of the upper deck was some

distance aft of amidships and sometimes departures were made from the parabolic sheer profile. The value of

sheer and particularly the sheer forward was to increase the height of the deck above water (the ?height of

platform‘ as it was called ) and this helped to prevent water being shipped when the vessel was moving through

rough sea. The reason for the abolition of sheer in some modern ships is that their depths are so great that

additional height of the deck above water at the fore end is unnecessary from a seakeeping point of view.

Deletion of sheer also tends to make the ship easier to construct, but on the other hand it could be said that the appearance of the ship suffers in consequence.

Camber

Camber or round of beam is beam is defined as the rise of the deck of the ship in going from the side to the centre as shown in Figure 3(a). The camber curve used to be parabolic but here again often nowadays straight line camber curves are used or there may be no camber at all on decks. Camber is useful on the weather deck of a ship from a drainage point of view, but this may not be very important since the ship is very

rarely upright and at rest. Often, if the weather deck of a ship is cambered, the lower decks particularly in passenger ships may have no

camber at all, as this makes for horizontal decks in accommodation which is an advantage.

Camber is usually stated as its value on the moulded breadth of the ship and standard camber was taken as one-fiftieth of the breadth. The camber on the deck diminishes towards the ends of the ship as the deck breadths become smaller.

Bilge radius

An outline of the midship section of a ship is shown in Figure 3(a). In many ?full‘ cargo ships the section is

virtually a rectangle with the lower corners rounded off. This part of the section is referred to as the ?bilge‘ and the shape is often circular at this position. The radius of the circular arc forming the bilge is called the ?bilge radius‘. Some designers prefer to make the section some curve other than a circle in way of the bilge. The curve would

have a radius of curvature which increases as it approaches the straight parts of the section with which it has to link up.

Rise of floor

The bottom of a ship at amidships is usually flat but is not necessarily horizontal. If the line of the flat bottom is continued outwards it will intersect the breadth moulded line as shown in Figure 3(a). The height of this