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In page Sailing ship:

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Hull shapes for sailing ships evolved from being relatively short and blunt to being longer and finer at the bow.[1] By the nineteenth century, ships were built with reference to a half model, made from wooden layers that were pinned together. Each layer could be scaled to the actual size of the vessel in order to lay out its hull structure, starting with the keel and leading to the ship's ribs. The ribs were pieced together from curved elements, called futtocks and tied in place until the installation of the planking. Typically, planking was caulked with a tar-impregnated yarn made from manila or hemp to make the planking watertight.[2] Starting in the mid-19th century, iron was used first for the hull structure and later for its watertight sheathing.[3]