Raft
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A raft is any structure, with a flat top, that floats on water. It is the most basic of boat design, characterized by the absence of a hull. Instead, rafts are kept afloat using any combination of buoyant materials such as wood, sealed barrels, or inflated air chambers.
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[edit] Rafts built by humans
Traditional or primitive rafts are constructed of wood or reeds. Modern rafts may also use pontoons, drums, or extruded polystyrene blocks. Inflatable rafts use durable, multi-layered rubberized fabrics. Depending on its use and size, it may have a superstructure, masts, or rudders.
Timber rafting is used by the logging industry for the transportation of logs, by tying them together into rafts, and drifting or pulling them down a river. This method was very common up until the middle of the 20th century but is now used only rarely.
The type of raft used for recreational rafting is almost exclusively an inflatable boat, manufactured of flexible materials for use on whitewater.
[edit] Nonanthropogenic rafts
In biology, particularly in island biogeography, non-anthropogenic rafts are an important concept. Such rafts consist of matted clumps of vegetation that has been swept off the dry land by a storm, tsunami, tide, earthquake or similar event; in modern times they sometimes also incorporate other kinds of flotsam and jetsam, e.g. plastic containers. They stay afloat by its natural buoyancy and can travel for hundreds, even thousands of miles and ultimately are destroyed by wave action and decomposition, or make landfall.
Biological rafts are important means of distribution for non-flying animals. For small mammals, amphibians and reptiles in particular, but for many invertebrates as well, such rafts of vegetation are often the only means by which they could reach and – if they are lucky – colonize oceanic islands before human-built vehicles provided another mode of transport.
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