A floatplane is a type of seaplane, with slender pontoons (known as "floats") mounted under the fuselage; only the floats of a floatplane normally come into contact with water, with the fuselage remaining above water. A floatplane is opposed to a flying boat, which uses its fuselage for buoyancy like a ship's hull. However in popular parlance the term "seaplane" is sometimes used to refer exclusively to floatplanes, but not flying boats.
A floatplane is essentially the best development of land-based aircraft, with floats mounted under the fuselage instead of wheeled landing gear. Floatplanes are traditionally more popular than flying boats for small aircraft designs, since it permits a single piston engine to be installed in the conventional manner, that is at the nose of the fuselage (this could be done on flying boats only by mounting the engine high above the fuselage). Moreover, the fuselages of floatplanes are typically more aerodynamic than flying boats; while the large floats underneath the fuselages inevitably impose extra drag and weight to floatplanes, rendering them less manoeuvrable during flight than their land-based counterparts, historically it did little to affect their speed, as the contestants in the Schneider Trophy demonstrated.
There are two basic arrangements for floats on floatplanes. One is the single float design, in which a single large float is mounted directly underneath the fuselage, with smaller stabilizing floats underneath the wings. The other is the twin float design, with a pair of floats mounted beneath the wing roots, in place of wheeled landing gear. The main advantage of the single float design is its rough sea landing capability: the large central float is directly attached to the fuselage, this being the strongest part of the aircraft structure, while the small floats under the outer wings provide the aircraft with good lateral stability. However the twin float design facilitates mooring and boarding, and in the case of a military floatplane, leaves the belly free to carry a torpedo or a heavy bombload. Whatever the float layout, a floatplane tends to be less stable on water than flying boats.
Floatplanes first appeared during World War I, and remained in widespread naval use until World War II. Most larger warships of that era carried floatplanes - typically four for each battleship, and one to two for each cruiser - to be launched by catapults; their main task was to spot targets over the horizon for the big guns. Other floatplanes, sometimes carried on seaplane tenders, were used for bombings, reconnaissance, air-sea rescue, and even as fighters.
During the interwar period, civilian use of floatplanes were rather rare, given the larger fuselage (hence greater payload) of flying boats; however floatplane racing aircraft were very popular, as exemplified by those which participated the Schneider Trophy.
After World War II, the advent of radar and helicopters, and the advanced development of aircraft carriers and land-based aircraft, saw the demise of military seaplanes. This, coupled with the increased availability of civilian airstrips, have greatly reduced the number of flying boats being built. However, numerous modern civilian aircraft have floatplane variants, most of these are offered as third-party modifications under a supplemental type certificate (STC), although there are several aircraft manufacturers that build floatplanes from scratch. These floatplanes have found their niche as "bush" aircraft, for light duty transportation to lakes and other remote areas, as well as to small/hilly islands without proper airstrips. They may operate on a charter basis (including, but not limited to, pleasure flights), provide scheduled service, or be operated by residents of the area for private, personal use.