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14-07-2015, 00:36


The representation of the shape of a ship on paper is not easy. In the late 18th and early 19th centuries naval architects devised a standard convention for producing plans of hull shapes using a series of three plans to represent the shape of the hull. The first plan is a side view of the vessel viewed perpendicular to the keel and is known as the sheer plan or elevation. The second plan is a view from the fore and aft of the vessel, usually with the planks removed, showing the outlines of the timbers and is known as the body plan or projection. Finally the half-breadth or horizontal plane is a view of the hull from below. Onto these plans various sections are drawn which help to define the surface. The sections can be imagined to be formed by slicing the solid hull into a series of slices of equal thickness in the three different planes. Thus the horizontal slices form a series of water lines, the vertical longitudinal slices form a series of sheer lines, and the vertical lateral slices form the shapes that the frames will have. Additionally, the body plan sometimes shows the diagonals, which are lines that would be formed if the ship was cut longitudinally, parallel to the keel, at an angle, usually 45°. A number of authors (Chapman, 1769; Steel, 1805) show early ship drafts which are useful reference material and Lyon (1974) gives a good introduction to the various types of ships’ plans and their sources in the National Maritime Museum at Greenwich.

There are a number of computer-based programs which enable ships’ lines to be drawn from a table of offsets. These programs usually allow the entry of X, Y, and Z coordinates for various sections of the hull and then calculate and produce a series of line drawings (Figure 11.16).


Figure 11.16 Line drawing of a Yatra Dhoni in Sri Lanka. The line drawing enables naval architects to make calculations about the performance and capacity of the vessel. This plan is used in the construction of the vessel. (Courtesy of Brian Richards, Department of Marine Archaeology, Western Australian Maritime Museum.)


Figure 11.17 Large-size calipers used to measure diameters. (Courtesy of Brian Richards, Department of Marine Archaeology, Western Australian Maritime Museum.)

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