Raft

A raft is any flat structure for support or transportation over water.G. & C. Merriam Co., Websters New Collegiate Dictionary, 1976, It is usually of basic design, characterized by the absence of a hull. 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. Rafts are an ancient mode of transport; naturally occurring rafts such as entwined vegetation and pieces of wood have been used to traverse water since the dawn of humanity.

Human-made rafts

Traditional or primitive rafts were constructed of wood, bamboo, or reeds; early buoyed or float rafts use inflated animal skins or sealed clay pots, which are lashed together. Modern float rafts may also use pontoons, drums, or extruded polystyrene blocks. 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.

Large rafts made of balsa logs and using sails for navigation were important in maritime trade on the Pacific Ocean coast of South America from pre-Columbian times until the 19th century. Voyages were made to locations as far away as Mexico, and many trans-Pacific voyages using replicas of ancient rafts have been undertaken to demonstrate possible contacts between South America and Polynesia.Smith, Cameron M. and Haslett, John F. (1999), "Construction and Sailing Characteristics of a Pre-Columbian Raft Replica", Bulletin of Primitive Technology, pp. 13–18

Rafts used for recreational rafting are almost exclusively inflatable rafts, manufactured of flexible materials such as PVC, hypalon, polyurethane, and nylon. These materials are resistant to the collisions and heavy wear the boats experience when traveling through whitewater. Whitewater rafts are also designed with high rocker, a raised bow and stern, which allows them to pass over waves and obstacles more easily. Most have drain holes in the floor to prevent the boat from becoming swamped with water.

Natural rafts In biology, particularly in island biogeography, non-manmade 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 kind of flotsam and jetsam, e.g. plastic containers. They stay afloat by their natural buoyancy and can travel for hundreds, even thousands of miles and are ultimately destroyed by wave action and decomposition or make landfall.

Rafting events are important means of oceanic dispersal for non-flying animals. For amphibians, reptiles, and small mammals, in particular, but for many invertebrates as well, such rafts of vegetation were often the only means by which they could reach and – if they were lucky – colonize oceanic islands before human-built vehicles provided another mode of transport.

Image gallery

Bron en licentie