A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains speed, the hydrofoils lift the boat's hull out of the water, decreasing drag and allowing greater speeds.
Forlanini's hydrofoil over Lake Maggiore, 1906
Alexander Graham Bell's HD-4 on a test run, c. 1919
Meteor
Raketa
An airfoil or aerofoil is a streamlined body that is capable of generating significantly more lift than drag. Wings, sails and propeller blades are examples of airfoils. Foils of similar function designed with water as the working fluid are called hydrofoils.
Lift and drag curves for a typical airfoil
An airfoil section is displayed at the tip of this Denney Kitfox aircraft, built in 1991.
Airfoil of a Kamov Ka-26 helicopter's lower rotor blade