The very first hull is thought to have consisted of a hollowed out tree bole and was a Stone Age invention--in effect the first canoe. Hull construction then proceeded to keeled hulls, including ballast and on to modern double steel hulls with waterproof sections.
In the very latest sailing ships, hulls are often made of layers of foam and plastic, forming composite hulls, with a minimum of weight. Variations on the single hull can be found with outriggers, and craft with more than one hull, called multihulls.
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