As the boat moves through the water, the hydrofoils lift its hull partly out of the water. The less of a boat there is in the water, the faster and more easily it can move. The lift from the foils is rather like the lift provided by the wings of an aeroplane but the foils are very much smaller than aircraft wings.

There are two main type of foils: the surface-piercing type and the fully-submerged type. Surface-piercing foils are the simpler type. They were developed by a Swiss, Baron von Schertel. His 30-seater craft started the world's first passenger hydrofoil service in 1953, on Lake Maggiore on the borders of Italy and Switzerland. When viewed from the front of the craft, a pair of surface-piercing foils is V-shaped. The amount they lift the hull depends on how much of the foils is submerged. Fully-submerged foils were developed by an Englishman, Christopher Hook. The amount of lift they provide can be varied. Foils are made from high-strength alloys (mixtures of metals).

Because of the size of the foils, engineers believe that it is not possible to build a hydrofoil craft bigger than about 1,000 tons. The largest on service today weigh a few hundred tons. The top speed of normal hydrofoils is about 50 knots, but craft with specially designed foils can travel at more than 80 knots.

A hydrofoil craft is usually propelled by one or more propellers (or 'screws') like those of a motor-boat. Power for driving the propellers is supplied by diesel engines or gas turbines. In another method of propulsion, water jets (driven by gas turbines) are used instead of propellers.

The hydrofoil was first invented more than 100 years ago, but it was not until the early 1950s that really successful craft were built. Various types are now in use in coastal waters and on rivers in many parts of the world, and some can carry well over 200 passengers. The Soviet Union has a very large number of hydrofoils.