Hydrofoil, which lifts the hull out of the water, was popular in the ’60s and ’70s, mostly with successful military and commercial passenger boats.
Although hydrofoil can reduce both the effect of waves and the drag at high speed, hydrofoils are vulnerable to objects in the water and expensive to build.
Foilborne operations are limited as wave height exceeds the hydrofoil’s strut length. These have caused a steady decline in interest and popularity, though in the past several years, the boating industry has seen new hydrofoil projects.
A hydrofoil boat uses lifting elements (foils) to create an upward force, which raises the hull out of the water (takeoff). The lifting force is a result of a pressure difference in the flow field above and beneath the foils. This principle is comparable to wings (aerofoils) of an aircraft.
Yet hydrofoils only generate lift when they move through water—in order to take off and overcome the total drag, extra power and an efficient hull is needed. With the hull out of the water and the foils submerged, the hydrofoil boat is “foilborne.” From then, the foils only need to keep the boat in a good seakeeping and steerable condition.
Foils are most commonly in a T- or L-shape, and the most common system is the fully submerged type, which is more stable and less a subject to the effects of sea waves.
Up to 65 knots
The French sailing hydrofoil Hydroptère is a state-of-the-art vessel that combines leading technology from both the aeronautic and marine industries. The project started with a childhood dream from Alain Thébault.
In 2009 Hydroptère broke the outright sailboat speed world record of more than 51 knots in just 30 knots of wind. Today this record stands at 65 knots by the VSR2 Sailrocket.
In the America’s Cup, hydrofoil is the established standard, where catamarans like an AC72 powered by a tall wing sail are able to hydrofoil at speeds of almost three times the wind speed.
These hydrofoils also exist in smaller sizes, with hydrofoil boards to surf, kite or wake.