A float (also called a pontoon) is an airtight hollow structure, similar to a

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

, designed to provide

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

in water. Its principal applications are in watercraft hulls,

aircraft floats A floatplane is a type of seaplane with one or more slender floats mounted under the fuselage to provide buoyancy. By contrast, a flying boat uses its fuselage for buoyancy. Either type of seaplane may also have landing gear suitable for land, ...

, floating piers,

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...

pontoon bridges A pontoon bridge (or ponton bridge), also known as a floating bridge, is a bridge that uses float (nautical), floats or shallow-draft (hull), draft boats to support a continuous deck for pedestrian and vehicle travel. The buoyancy of the support ...

, and marine engineering applications such as salvage.

Applications

Floats make up the multipart hulls of

catamaran A catamaran () (informally, a "cat") is a watercraft with two parallel hull (watercraft), hulls of equal size. The wide distance between a catamaran's hulls imparts stability through resistance to rolling and overturning; no ballast is requi ...

s and

trimaran A trimaran (or double-outrigger) is a multihull boat that comprises a main hull and two smaller outrigger hulls (or "floats") which are attached to the main hull with lateral beams. Most modern trimarans are sailing yachts designed for recrea ...

s and provide buoyancy for

floatplane A floatplane is a type of seaplane with one or more slender floats mounted under the fuselage to provide buoyancy. By contrast, a flying boat uses its fuselage for buoyancy. Either type of seaplane may also have landing gear suitable for land, ...

seaplane A seaplane is a powered fixed-wing aircraft capable of takeoff, taking off and water landing, landing (alighting) on water.Gunston, "The Cambridge Aerospace Dictionary", 2009. Seaplanes are usually divided into two categories based on their tech ...

s and

houseboat A houseboat is a boat that has been designed or modified to be used primarily for regular dwelling. Most houseboats are not motorized, as they are usually moored or kept stationary, fixed at a Berth (moorings), berth, and often tethered to ...

s. They are used in pontoon bridges, floating piers, and floats anchored to the seabed for recreation or dockage. They are also used in

shipbuilding Shipbuilding is the construction of ships and other Watercraft, floating vessels. In modern times, it normally takes place in a specialized facility known as a shipyard. Shipbuilders, also called shipwrights, follow a specialized occupation th ...

and marine salvage, often deployed uninflated then pressurized to raise a sunken object. In military, floats are used as pontoon bridges or transportation platforms for heavier vehicles or machinery. In popular usage, the term ''pontoon'' can refer to any of several of the following objects that make use of nautical floats.

Pontoon boat

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 platform

Floats are used as floating commercial docks and work areas, and as rafts for swimming, diving, and other recreational activities. Most familiarly, they are anchored seasonally at beaches and lake shores, or year-round where weather permits. They are variously supported by foam-filled plastic floats, closed cell foam, or air-filled vessels (such as used 55-gallon drums). Known as "swim floats" in North America, they are known simply as "pontoons" in Australia and New Zealand.

In aquaculture

Various forms of floating platforms, tanks, growing cages, and work areas are used in

, all employing some form of artificial buoyancy generically known as "floats".

Floating dock

A floating dock, floating pier or floating jetty consists of a platform or ramp supported by nautical floats. It is sometimes joined to the shore with a gangway but can be laid out the whole way from the shore to the end. This type of pier maintains a fixed vertical relationship to watercraft secured to it.

Salvage pontoon

A salvage pontoon, sometimes known as a lift bag, is a pontoon used to raise a sunken watercraft, or provide additional buoyancy. Salvage pontoons can be either flexible and inflatable, or a fixed size. Usually cylindrical in shape, they can be used either in a ship's internal spaces, or externally. In addition to raising sunken vessels, they are also commonly used for long tows, for providing buoyancy to cables and so on.

Pontoon bridge

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, but not all, pontoon bridges are temporary, used in wartime and civil emergencies. Seattle in the US and Kelowna in British Columbia, Canada are two places with permanent pontoon bridges, see William R. Bennett Bridge in British Columbia and these in Seattle: Lacey V. Murrow Memorial Bridge,

Evergreen Point Floating Bridge The Evergreen Point Floating Bridge, also known as the 520 Bridge and officially the Governor Albert D. Rosellini Bridge, is a floating bridge that carries Washington State Route 520 across Lake Washington from Seattle to its eastern suburbs ...

and Homer M. Hadley Memorial Bridge.

Floatplane

(float plane or pontoon plane) is a type of seaplane with one or more floats mounted under the fuselage to provide buoyancy. Floats are streamlined to be both hydro- and aerodynamic.

Construction

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 Fiberglass (American English) or fibreglass ( Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass c ...

. Other techniques include those of traditional wooden boatbuilding as well as

plywood Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboa ...

over wooden ribs or metal sheets over metal ribs (aluminium or steel), reflecting the prevailing practice in aircraft and boats. In most cases, the decking surface on top of the pontoon is made from glass-reinforced plastic ( GRP) or

composite lumber Composite or compositing may refer to: Materials * Composite material, a material that is made from several different substances ** Metal matrix composite, composed of metal and other parts ** Cermet, a composite of ceramic and metallic material ...

. In model building, floats can easily be carved out of solid blocks or laminated sheets of foam.{{Failed verification, date=September 2021

Gallery

Image:Catamaranedan.jpg, Small open

Image:Dragonflyextended.jpg, Foldable trimaran with the floats in extended position File:Port pontoon of a Sikorsky Sea King.jpg, A helicopter pontoon that may be augmented by an inflatable emergency pontoon shown in black File:RV Chetlo pontoon boat contruction.jpg, The underside of a pontoon boat during construction

References

Buoyancy devices