A structure which, when moved rapidly through water, generates lift
in exactly the same way and for the same reason as does the airfoil.
It is usually mounted beneath a vessel (also called a hydrofoil). Much of
a conventional boat's power is spent in overcoming the drag
(resistance) of the water; as a hydrofoil vessel builds up speed, it lifts
out of the water until only a small portion of it (struts, hydrofoils, and
propeller) is in contact with the water. Thus drag is reduced to a minimum.
Hydrofoils can exceed 125 km/h as compared with conventional craft, whose
maximum speeds rarely approach 80 km/h.
|Common hydrofoil configurations
(left) surface-piercing foils; (right) fully submerged foils