Representing the hull form

The hull form is portrayed graphically by the lines plan or sheer plan (Figure 3.4). This shows the various curves of intersection between the hull and the three sets of orthogonal planes. Because the ship is symmetrical, by convention only one half is shown. The curves showing the intersections of the vertical fore and aft planes are grouped in the sheer profile; the waterlines are grouped in the half breadth plan; and the sections by transverse planes in the body plan. In merchant ships the transverse sections are numbered from aft to forward. In warships they are numbered from forward to aft although the forward half of the ship is still, by tradition, shown on the right hand side of the body plan. The distances of the various intersection points from the middle line plane are called offsets.

Clearly the three sets of curves making up the lines plan are interrelated as they represent the same three dimensional body. This interdependency

Naval Architecture Programs


is used in manual fairing of the hull form, each set being faired in turn and the changes in the other two noted. At the end of the iteration the three sets will be mutually compatible. Fairing is usually now carried out by computer. Indeed the form itself is often generated directly from the early design processes in the computer. Manual fairing is done first in the design office on a reduced scale drawing. To aid production the lines used to be laid off, and refaired, full scale on the floor of a building known as the mould loft. Many shipyards now use a reduced scale, say one-tenth, for use in the building process. For computer designed ships the computer may produce the set of offsets for setting out in the shipyard or, more likely, it will provide computer tapes to be used in computer aided manufacturing processes.

In some ships, particularly carriers of bulk cargo, the transverse cross section is constant for some fore and aft distance near amidships. This portion is known as the parallel middle body.

Where there are excrescences from the main hull, such as shaft bossings or a sonar dome, these are treated as appendages and faired separately.

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