
A pontoon boat, like this small pleasure boat, typically floats and balances by means of two pontoons mounted lengthwise.
A 'pontoon' is a flat-bottomed
boat or the floats used to support a structure on water. It may be simply constructed from closed
cylinders such as pipes or barrels or fabricated as boxes from
metal or
concrete. These may be used to support a simple platform, creating a
raft. A raft supporting a house-like structure is one form of
houseboat.
Pontoon boats generally run slower and are less likely to cause harm to themselves or other vessels, and are thus less expensive to insure. As such, they are the most popular vessel style for rental operations. They also offer the largest value in terms of capacity to price.
Pontoons are also used as small
vehicle ferries to cross rivers and lakes in many parts of the world, especially in
Africa. Pontoon ferries may be motorised, such as the
Kazungula Ferry across the
Zambezi River, or powered by another boat, or pulled by cables. A type of ferry known as the
cable ferry (called 'punts' in
Australia and
New Zealand) pull themselves across a river using a motor or human power applied to the cable, which also guides the pontoon.
History
Pontoon bridges have been used by military forces since ancient times.
The invention of the pontoon motorboat in the USA is credited to a
Minnesota farmer
[1].
"Pontoon" is also the name of a yearly anthology of Washington State poets published by the Floating Bridge Press. http://www.scn.org/floatingbridge/main.html
Applications

Pontoon bridge part on truck.
Pontoons may be used to support docks or
floating bridges. In the case of a dock the entire device is sometimes called a pontoon.
Pontoons of sophisticated construction and shape are used to support aircraft so they may be operated from water. Such pontoons may also contain
landing gear so that the aircraft may operate on both land and water. Such aircraft are called amphibious
floatplanes. Floatplanes are distinct from
flying boats in which the aircraft fuselage forms a watertight hull.
Pontoons are useful in the salvage of sunken vessels. They may be used to support
cranes that lift the boat via cables. In other cases they may be sunk and attached to the vessel underwater. The water inside the pontoon is then displaced with compressed air to float the pontoon.
The "Pontoon effect"
See the main article:
Pontoon effect
Notes
1. "An Idea that Started an Industry", Weeres Industries Corp., St. Cloud, Minnesota