Planing (/ˈpleɪnɪŋ/ PLAY-ning) is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift (buoyancy).
Many forms of marine transport make use of planing, including fast ferries, racing boats, seaplanes, and water skis. Most surfboards are planing or semi-planing hulls. Beyond planing, fast vessel designs have seen a transition to hydrofoil designs.
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Dinghy racing is a competitive sport using dinghies, which are small boats which may be rowboats, have an outboard motor, or be sailing dinghies. Dinghy racing has affected aspects of the modern sailing dinghy, including hull design, sail materials and sailplan, and techniques such as planing and trapezing.
A seaplane is a powered fixed-wing aircraft capable of taking off and landing (alighting) on water. Seaplanes are usually divided into two categories based on their technological characteristics: floatplanes and flying boats; the latter are generally far larger and can carry far more. Seaplanes that can also take off and land on airfields are in a subclass called amphibious aircraft, or amphibians. Seaplanes were sometimes called hydroplanes, but currently this term applies instead to motor-powered watercraft that use the technique of hydrodynamic lift to skim the surface of water when running at speed.
The use of seaplanes gradually tapered off after World War II, partially because of the investments in airports during the war but mainly because landplanes were less constrained by weather conditions that could result in sea states being too high to operate seaplanes while landplanes could continue to operate. In the 21st century, seaplanes maintain a few niche uses, such as for aerial firefighting, air transport around archipelagos, and access to undeveloped or roadless areas, some of which have numerous lakes. In British English, seaplane is sometimes used specifically to refer to a floatplane, rather than a flying boat.
A PT boat (short for patrol torpedo boat) is a motor torpedo boat used by the United States Navy in World War II. These vessels were small, fast, and inexpensive to build, and were valued for their maneuverability and speed. However, PT boats were hampered at the beginning of the war by ineffective torpedoes, limited armament, and comparatively fragile construction that limited some of the variants to coastal waters. In the US Navy they were organized in Motor Torpedo Boat Squadrons (MTBRONs).
PT boats were very different from the first generation of torpedo boats, which had been developed at the end of the 19th century and featured a displacement hull form. These first generation torpedo boats rode low in the water, displaced up to 300 tons, and had a top speed of 25 to 27 kn (46 to 50 km/h). During World War I Italy, the US, and UK developed the first high-performance, gasoline-powered motor torpedo boats (often with top speeds over 40 kn (74 km/h)) and corresponding torpedo tactics, but these projects were all quickly disbanded after the Armistice. Design of World War II PT boats continued to exploit some of the advances in planing hull design borrowed from offshore powerboat racing and used multiple lightweight but more powerful marinized aircraft-derived V-12 engines, and thus were able to advance in both size and speed.
A hydroplane (or hydro, or thunderboat) is a fast motorboat, where the hull shape is such that at speed, the weight of the boat is supported by planing forces, rather than simple buoyancy.
A key aspect of hydroplanes is that they use the water they are on for lift rather than buoyancy, as well as for propulsion and steering: when travelling at high speed water is forced downwards by the bottom of the boat's hull. The water therefore exerts an equal and opposite force upwards, lifting the vast majority of the hull out of the water. This process, happening at the surface of the water, is known as 'foiling'.