Historically, watercraft have been divided into two main categories.
Rafts, which gain their buoyancy from the fastening together of components that are each buoyant in their own right. Generally, a raft is a "flow through" structures, whose users would have difficulty keeping dry as it passes through waves. Consequently, apart from short journeys (such as a river crossing) their use is confined to warmer regions (roughly 40° N to 40° S). Outside this area, use of rafts at sea are impracticable due to the risks of exposure to the crew. Rafts divide into a number of types bundle raft can be made from, for example,papyrus that has been tied into bundles. These can even be shaped
Boats andships, which float by having the submerged part of their structure exclude water with a waterproof surface, so creating a space that contains air, as well as cargo, passengers, crew, etc. In total, this structure weighs less than the water that would occupy the same volume.[2]: 7–8
The design of watercraft requires a tradeoff among internal capacity (tonnage), speed andseaworthiness. Tonnage is important for transport of goods, speed is important forwarships and racing vessels, and the degree of seaworthiness varies according to the bodies of water on which a watercraft is used. Regulations apply to larger watercraft, to avoidfoundering at sea and other problems. Design technologies include the use ofcomputer modeling andship model basin testing before construction.[4]
Watercraft propulsion can be divided into five categories.
Water power is used by drifting with a river current or a tidal stream. An anchor or weight may be lowered to provide enoughsteerage way to keep in the best part of the current (as indrudging) or paddles or poles might be used to keep position.
Human effort is used through apole pushing against the bottom of shallow water, orpaddles oroars operating in the surface of the water.
Towing is used, either from the land, such as the bank of acanal, with the motive power provided bydraught animals, humans or machinery, or one watercraft may tow another.
Mechanical propulsion uses amotor whose power is derived from burning a fuel or stored energy such as batteries. This power is commonly converted into propulsion bypropellers or bywater jets, withpaddle wheels being a largely historical method.[2]: 33
Any one watercraft might use more than one of these methods at different times or in conjunction with each other. For instance, early steamships often set sails to work alongside the engine power. Before steam tugs became common, sailing vessels wouldback and fill their sails to maintain a good position in a tidal stream while drifting with the tide in or out of a river. In a modernyacht, motor-sailing – travelling under the power of both sails and engine – is a common method of making progress, if only in and out of harbour.[2]: 33–34 [5]: 199–202 [6]
^McGrail, Sean (2014).Early ships and seafaring : water transport beyond Europe. Barnsley.ISBN9781473825598.{{cite book}}: CS1 maint: location missing publisher (link)
^abcMcGrail, Sean (2014).Early ships and seafaring : European water transport. South Yorkshire, England: Pen and Sword Archaeology.ISBN9781781593929.
^Tupper, Eric (1996).Introduction to Naval Architecture. Oxford, England: Butterworth-Heinemann.
^Harland, John (1984).Seamanship in the Age of Sail: an account of the shiphandling of the sailing man-of-war 1600–1860, based on contemporary sources. London: Conway Maritime Press.ISBN978-1-8448-6309-9.
