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 most unique things about these boats is that they only use the water they're on for propulsion and steering--when going full speed they are primarily held aloft by a principle of aerodynamics known as "planing", with only a tiny fraction of their hull actually touching the water.

Hydroplane design

The basic principle of the hull design of most hydroplanes has remained much the same since the beginning of the sport: 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 like that. The goal is to keep as little of the boat as possible from touching the water, since water gives more drag than air.

One of the few significant attempts at a radically different design 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, other than 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.

Unlimited hydroplane engines

The aerodynamics industry has been the main source of engines for the boats. For the first few decades, they used surplus World War II-era internal-combustion airplane engines. The manufacturers of the two most commonly used engines are Rolls Royce and their Allison division. The loud roar of these engines earned hydroplanes the nickname thunderboats.

Donald Campbell attempted world speed records in a jet engine powered hydroplane, Bluebird in the early 1950s.

Starting in 1980, they have increasingly used Vietnam War-era turbine engines from helicopters (actually, in 1973-1974, one hydroplane used turbine engines in races to test the technology). The manufacturer of the most commonly used turbines is Lycoming.

Efforts have occasionally been made to use automotive engines, but they generally haven't been proven to be competitive.

External link

• Nice set of pictures showing bow design evolution, from the Hydroplane and Raceboat Museum Also note the wood grain visible on some of the early boats--later hydros have used fiberglass and assorted hi-tech materials