thumb|Sketch by F.E. Paris (1841) showing construction of a native peruvian balsa raftA
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.
Rafts built by humans
Children successfully test their raft, in Brixham harbour, south Devon, England. The raft is made from wooden poles, rope and blue barrels.
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.
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.
See also
