Raft
Overview
 
A raft is any flat structure for support or transportation over water. It is the most basic of boat
Boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

 design, characterized by the absence of a hull
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

. 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
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

, sealed barrel
Barrel
A barrel or cask is a hollow cylindrical container, traditionally made of vertical wooden staves and bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. A small barrel is called a keg.For example, a...

s, or inflated air chambers (such as pontoons), and are typically not propelled by an engine.
Traditional or primitive rafts are constructed of wood or reeds
Phragmites
Phragmites, the Common reed, is a large perennial grass found in wetlands throughout temperate and tropical regions of the world. Phragmites australis is sometimes regarded as the sole species of the genus Phragmites, though some botanists divide Phragmites australis into three or four species...

.
Encyclopedia
A raft is any flat structure for support or transportation over water. It is the most basic of boat
Boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

 design, characterized by the absence of a hull
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

. 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
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

, sealed barrel
Barrel
A barrel or cask is a hollow cylindrical container, traditionally made of vertical wooden staves and bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. A small barrel is called a keg.For example, a...

s, or inflated air chambers (such as pontoons), and are typically not propelled by an engine.

Man-made rafts

Traditional or primitive rafts are constructed of wood or reeds
Phragmites
Phragmites, the Common reed, is a large perennial grass found in wetlands throughout temperate and tropical regions of the world. Phragmites australis is sometimes regarded as the sole species of the genus Phragmites, though some botanists divide Phragmites australis into three or four species...

. Modern rafts may also use pontoons
Pontoon (boat)
A pontoon is a flotation device with buoyancy sufficient to float itself as well as a heavy load. A pontoon boat is a flattish boat that relies on pontoons to float. Pontoons may be used on boats, rafts, barges, docks, floatplanes or seaplanes. Pontoons may support a platform, creating a raft. A...

, drums
Drum (container)
A drum is a cylindrical container used for shipping bulk cargo. Drums can be made of steel, dense paperboard , or plastics, and are generally used for the transportation and storage of liquids and powders. Drums are often certified for shipment of dangerous goods...

, or extruded polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...

 blocks. Inflatable rafts use durable, multi-layered rubberized fabrics. Depending on its use and size, it may have a superstructure
Superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships...

, masts, or rudders.

Timber rafting
Timber rafting
Timber rafting is a log transportation method in which logs are tied together into rafts and drifted or pulled across a water body or down a flatter river. It is arguably the second cheapest method of transportation of timber, next after log driving...

 is used by the logging
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...

 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
Rafting
Rafting or white water rafting is a challenging recreational outdoor activity using an inflatable raft to navigate a river or other bodies of water. This is usually done on white water or different degrees of rough water, in order to thrill and excite the raft passengers. The development of this...

 is almost exclusively an inflatable boat
Inflatable boat
An inflatable boat is a lightweight boat constructed with its sides and bow made of flexible tubes containing pressurised gas. For smaller boats, the floor and hull beneath it is often flexible. On boats longer than , the floor often consists of three to five rigid plywood or aluminium sheets fixed...

, manufactured of flexible materials for use on whitewater
Whitewater
Whitewater is formed in a rapid, when a river's gradient increases enough to disturb its laminar flow and create turbulence, i.e. form a bubbly, or aerated and unstable current; the frothy water appears white...

.

Nonanthropogenic rafts

In biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

, particularly in island biogeography
Island biogeography
Island biogeography is a field within biogeography that attempts to establish and explain the factors that affect the species richness of natural communities. The theory was developed to explain species richness of actual islands...

, non-anthropogenic rafts are an important concept. Such rafts consist of matted clumps of vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...

 that has been swept off the dry land by a storm
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...

, tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

, tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

, earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

 or similar event; in modern times they sometimes also incorporate other kinds of flotsam and jetsam
Flotsam and jetsam
In maritime law, flotsam, jetsam, lagan and derelict describe specific kinds of wreck.The words have specific nautical meanings, with legal consequences in the law of admiralty and marine salvage....

, e.g. plastic containers. They stay afloat by its natural buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 and can travel for hundreds, even thousands of miles and ultimately are destroyed by wave
Wave
In physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...

 action and decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...

, or make landfall.

Biological rafts are important means of distribution
Rafting event
Oceanic dispersal is a type of biological dispersal that occurs when organisms transfer from one land mass to another by way of a sea crossing on large clumps of floating vegetation. Such matted clumps of vegetation are often seen floating down major rivers in the tropics and washing out to sea,...

 for non-flying animals. For small mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, amphibians and reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s in particular, but for many invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s as well, such rafts of vegetation are often the only means by which they could reach and – if they are lucky – colonize ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

ic island
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

s before human
Human
Humans are the only living species in the Homo genus...

-built vehicles provided another mode of transport
Mode of transport
Mode of transport is a term used to distinguish substantially different ways to perform transport. The most dominant modes of transport are aviation, land transport, which includes rail, road and off-road transport, and ship transport...

.

See also

  • Great Raft
    Great Raft
    The Great Raft was a gigantic logjam or series of "rafts" that clogged the Red and Atchafalaya Rivers and was unique in North America.-Origin:It has been speculated that the trees in the jams were knocked down by an impact event...

  • Kon-Tiki
    Kon-Tiki
    Kon-Tiki was the raft used by Norwegian explorer and writer Thor Heyerdahl in his 1947 expedition across the Pacific Ocean from South America to the Polynesian islands. It was named after the Inca sun god, Viracocha, for whom "Kon-Tiki" was said to be an old name...

  • Lifeboat (shipboard)
    Lifeboat (shipboard)
    A lifeboat is a small, rigid or inflatable watercraft carried for emergency evacuation in the event of a disaster aboard ship. In the military, a lifeboat may be referred to as a whaleboat, dinghy, or gig. The ship's tenders of cruise ships often double as lifeboats. Recreational sailors sometimes...

  • Pumice raft
    Pumice raft
    A pumice raft is a floating raft of pumice occasionally created by ocean-based volcanic activity.Volcanic activity in the South Pacific near Tonga on August 12, 2006 caused the emergence of a new island...


  • Raft of the Medusa
    Raft of the Medusa
    For other uses, See: Radeau The Raft of the Medusa is an oil painting of 1818–1819 by the French Romantic painter and lithographer Théodore Géricault . Completed when the artist was 27, the work has become an icon of French Romanticism...

  • Supertramp (ecology)
    Supertramp (ecology)
    In ecology, a supertramp species is any type of animal which follows the "supertramp" strategy of high dispersion among many different habitats, towards none of which it is particularly specialized...

  • Thor Heyerdahl
    Thor Heyerdahl
    Thor Heyerdahl was a Norwegian ethnographer and adventurer with a background in zoology and geography. He became notable for his Kon-Tiki expedition, in which he sailed by raft from South America to the Tuamotu Islands...

  • Poon Lim
    Poon Lim
    Poon Lim or Lim Poon BEM was a Chinese sailor who survived 133 days alone in the South Atlantic.-Castaway:...



External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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