The hydrofoil works on the same principles as the aerofoil. In fact, aerofoils work much more efficiently in water than in the air. The hull of a hydrofoil has similarities to a floating boat and when at rest, it does actually float on the water. At fast speed, wing-shaped foils underneath the hull force the foils to rise in the water and in turn lift the hull higher than the water level. As this action reduces friction, the hydrofoil has the ability to dart over waves. Hydrofoils can travel at up to three times the speed of the fastest floating vessels. Two common types of hydrofoil are the submerged foil and the surface-piercing foil.
The submerged foil is self-explanatory. As the name suggests it stays submerged under the water at all times. This foil is controlled by a sonar system situated on the hydrofoil. Its function is to detect the height of oncoming waves. A signal is sent to the foil which allows it to change angle and adjust accordingly to the required lift. With this technique the foil adapts to the oncoming waves, evening out the ascent and descent which assures a stable ride.
The second type of foil is the surface-piercing foil. The amount of lift produced is determined by the depth of each foil in the water. The deeper the foil the greater the lift. This enables the craft to rise as it journeys into the apex of a wave. As it commences into calmer waters, the lift lessens, and the foil then begins to submerge. This method allows the hydrofoil to follow the contours of waves, rather than plowing through them.
