A hydroplane is a type of boat that uses air to raise itself almost completely out of the water and is capable of obtaining very high speeds. The typical hydroplane is constructed with a very wide bow consisting of two sponsons — one on each side of the boat — and a narrow stern. The common engine used in modern boats is a gas turbine, which replaces the piston aircraft-style engines of the earlier hydroplane designs. The bottom of the boat is designed to trap air under the bow of the boat and hold it between the sponsons as the high speed of the propeller raises the stern out of the water. This leaves the boat to ride on a cushion of air with only the bottom half of the propeller and the very bottom edge of the sponsons contacting the water.
This boat design is capable of producing such great speeds because the water's resistance is eliminated by raising the boat out of the water on the air cushion. With this great speed comes great peril, and the boat is constantly on the verge of becoming airborne and actually flipping over. This type of accident is known as a blow over in hydroplane racing terms. The boat's driver or pilot is able to manipulate small, wing flap-type devices in the front of the boat to correct and adjust the boat's attitude in the water. The problem comes in the form of wind gusts blowing across the water in the boat's path.
If the pilot is unable to correctly adjust to the changing wind, the boat can become airborne. Modern hydroplane design incorporates a breakaway cockpit complete with an on-board oxygen system to protect the driver in the event of such a crash. Prior to the introduction of this space-age design, a driver would be required to hold his breath until rescue personnel could reach the crashed boat and extract him. The main problem with this situation is that the driver would often be unconscious and unable to hold his breath, resulting in a driver fatality.
The propeller on a modern hydroplane can cost as much as a family sedan and occasionally more. Sharpened to a razor's edge, the hydroplane propeller is commonly of a three-blade design with only the bottom single blade contacting the water when at top speed. This type of design is known as a three-point design, with the hydroplane riding on the three points consisting of the two sponsons and the propeller.