What is a Hydrofoil?

               A hydrofoil is an underwater fin which consists of a flat or curved plane surface and is designed to lift a moving water vehicle by the reaction on its surface from the water through which it moves. Hydrofoils are used with ships and motor boats.

               The first hydrofoil was invented by an Italian called Forlanini in 1898. In 1918 a hydrofoil powered by an aircraft engine, gained the world’s water speed record. Hydrofoils were not widely used until the 1950s. After 1950 their use became common in military and commercial ships. By the 1970s hydrofoil craft were in operation in many places and speeds of upto 80 knots were achieved. During 1950s hydrofoils were developed in the United States, Canada and Russia.

               Now the question arises, how does a hydrofoil work?

               We know that water is 775 times heavier than air. And so very small hydrofoil wings can support relatively heavy boats. But since water puts great loads on boats, the hulls are usually built of high strength steel.

               The function of the hydrofoil is to raise the hull from the water so that the resistance caused by friction is reduced. This means the power needed to drive the boat at high speeds is reduced considerably. Another advantage of hydrofoil is that it can travel smoothly even in rough water.

               Hydrofoils are of such a shape that the flow of water over them causes a lift. As the boat’s speed increases it raises out of the water, supported on wing-like struts or foils. The hull lifts farther and farther out of the water until it is clear. Under this condition the only parts then in contact with the water are the hydrofoils and supporting struts and the propeller shaft.

               Hydrofoils are of various designs. While some boats have V-shaped or surface piercing hydrofoils, others have variable angle foils that can be adjusted. The purpose of all these is to lift the boat above water surface so that water friction does not produce any resistance. Hydrofoil boats can travel at a high speed. Nowadays hydrofoils are being used on a large scale in naval ships and commercial boats.

               The largest hydrofoil was launched by the Lockheed ship-building and Constructions Company, Washington, on 28 June, 1965. The 64.6 metre long hydrofoil has a service speed of 92 km per hour.