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A raft is any flat structure for support or transportation over water.〔G. & C. Merriam Co., ''Websters New Collegiate Dictionary'', 1976, ISBN 0-87779-339-5〕 It is the most basic of boat design, characterized by the absence of a hull. Although there are cross-over boat types that blur this definition, rafts are usually kept afloat by using any combination of buoyant materials such as wood, sealed barrels, or inflated air chambers (such as pontoons), and are typically not propelled by an engine. ==Human-made rafts== 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「raft」の詳細全文を読む スポンサード リンク
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