Hydroplane

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This article is about the hydroplane, a specific type of motorboat used in sport of hydroplane racing. See hydroplaning for other uses.

A hydroplane (or hydro, or thunderboat) is a very specific type of motorboat used exclusively for racing.

One of the unique things about these boats is that they only use the water they're on for propulsion and steering (not for floatation)--when going full speed they are primarily held aloft by a principle of fluid dynamics known as "planing", with only a tiny fraction of their hull actually touching the water.

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Hydroplane design

The basic hull design of most hydroplanes has remained relatively unchanged since the 1950s: two sponsons in front, one on either side of the bow; behind the wide bow, is a narrower, mostly rectangular section housing the driver, engine, and steering equipment. The aft part of the vessel is supported, in the water, by the lower half of the propeller, which is designed to operate semi-submerged at all times. The goal is to keep as little of the boat in contact with the water as possible, as water is much denser than air, and so exerts more drag on the vehicle than air does. Essentially the boat 'flies' over the surface of the water rather than actually travelling through it.

One of the few significant attempts at a radically different design since the three-point propriding design was introduced was referred to as Canard. It reversed the width properties, having a very narrow bow that only touched the water in one place, and two small outrigger sponsons in the back.

Early hydroplanes had mostly straight lines and flat surfaces aside from the uniformly curved bow and sponsons. The curved bow was eventually replaced by what is known as a pickle fork bow, where a space is left between the front few feet of the sponsons. Also, the centered single, vertical tail (similar to the ones on most modern airplanes) was gradually replaced by a horizontal stabilizer supported by vertical tails on either side of the boat. Later, as fine-tuning the aerodynamics became more important, the bottoms of the main hull have subtle curves to give the best lift.

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Unlimited hydroplane engines

The aviation industry has been the main source of engines for the boats. For the first few decades after World War II, they used surplus World War II-era internal-combustion airplane engines, typically Rolls-Royce Merlins or Griffons, or Allison V-1710s, all liquid-cooled V-12s. The loud roar of these engines earned hydroplanes the nickname thunderboats.

Donald Campbell attempted world speed records in the jet engined hydroplane, Bluebird in the early 1950s. The Ted Jones-designed Slo-Mo-Shun IV three-point, Allison-powered hydro set the water speed record (160.323 mph) in Lake Washington, off Seattle (USA)'s Sand Point, on June 26, 1950, breaking the previous (10+ year-old) record (141.740 mph/228.1 km/h) by almost 20 mph (32 km/h).

Starting in 1980, they have increasingly used Vietnam War-era turbine engines from helicopters (in 1973-1974, one hydroplane, U-95, used turbine engines in races to test the technology). The most commonly used turbine is the Lycoming T55, L-7C, used in the CH-47 Chinook.

Efforts have occasionally been made to use automotive engines, but they generally have not proven competitive.

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