John Sarkis, age 10, of Youngstown, Ohio, for his question:
WHAT IS A HYDROFOIL?
Hydrofoil boats (the word comes from the English word foil, meaning turn aside, and the Greek word hydro, meaning water) range from small experimental models to 100¬foot ocean going crafts. Most are built of lightweight material such as fiberglass or aluminum with the understructure, called the foils, being made of steel or other strong metal.
A hydrofoil is a craft that skims over water, usually at high speeds. Wing shaped structures extend into the water below the vessel and they actually lift the hull of the boat out of the water much as the wings of an airplane lift it into the air. When a hydrofoil boat is going fast enough, the hull flies above the surface with the foils and the propellers remaining beneath the surface.
Commercial hydrofoil vessels, powered by gas turbine, diesel, gasoline or even jet engines, can travel at speeds of between 30 and 40 knots with some experimental models having passed 60 knots. A knot, by the way, equals one nautical mile [1.15 statue milesI per hour,
Most hydrofoils have regular screw propellers at the stern. Some, however, use streams of water that are squirted into the air from the boat or into the water from the foils. This method of propulsion is called hydrojets.
Hydrofoil commuters are used to take passengers across New York Harbor. They provide smooth rides and create very little wakes. Even when the water is choppy with waves, the boats still hold very steady courses because so little is touching the water. Hydrofoil boats are especially well suited for use on rivers and inland waters, although they can also be used on the rough waters of open seas.
Leonardo da Vinci studied the hydrofoil action of wings but the principle wasn't applied until 1906 when an Italian inventor named Enrico Forlanini built and tested the first hydrofoil boat. In 1918 Alexander Graham Bell and his partner built one that was tested in Nova Scotia. Bell's craft held the hydrofoil speed record until the 1960s.
Much development with hydrofoil boats was done after World War II came to a close. Hans von Schertel, a German scientist who pioneered in designing surface¬piercing hydrofoil craft for commercial use, set up a firm in Switzerland with shipbuilders licensed in Italy and other countries. Russian developers also perfected large hydrofoil boats that are now used to carry passengers and cargo on rivers.