Floats (also called pontoons) are airtight hollow structures, similar to pressure vessels, designed to provide buoyancy in water. Their principal applications are in watercraft hulls and aircraft floats, floating pier and pontoon bridge construction, and marine engineering applications such as salvage.
Various objects that make use of floats are often referred to synecdochically as pontoons.
Floats make up the multipart hulls of catamarans and trimarans and provide buoyancy for floatplanes, seaplanes and houseboats. They are used in pontoon bridges, floating piers, and floats anchored to the seabed for recreation or dockage. They are also used in shipbuilding and marine salvage, often deployed uninflated then pressurized to raise a sunken object.
In popular usage, the term pontoon can refer to any of several of the following objects that make use of nautical floats.
A pontoon boat is a flattish boat that relies on nautical floats for buoyancy. Common boat designs are a catamaran with two pontoons, or a trimaran with three. In many parts of the world, pontoon boats are used as small vehicle ferries to cross rivers and lakes.
Anchored recreational platform
Raft-like platforms used for diving and other recreational activities are sometimes anchored at beaches and lake shores, often seasonally. Such platforms may be supported by foam-filled plastic floats or air-filled pontoons, and are known simply as "pontoons" in Australia and New Zealand. They may also be called swim floats.
A floating dock, floating pier or floating jetty consists of a platform or ramp supported by nautical floats. It is usually joined to the shore with a gangway. This type of pier maintains a fixed vertical relationship to watercraft secured to it.
A pontoon bridge (also known as a ponton bridge or floating bridge) uses floats or shallow-draft boats to support a continuous deck for pedestrian and vehicle travel. Most pontoon bridges are temporary, used in wartime and civil emergencies.
A floatplane (float plane or pontoon plane) is a type of seaplane with one or more slender pontoons mounted under the fuselage to provide buoyancy.
Pontoons for marine industrial uses are usually fabricated from steel. Pontoons as parts of watercraft and aircraft are more typically molded in glass-reinforced plastic. Other techniques include those of traditional wooden boatbuilding as well as plywood over wooden ribs or metal sheets over metal ribs (aluminium or steel), reflecting the prevailing practice in aircraft and boats. In model building, floats can easily be carved out of solid blocks or laminated sheets of foam.
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