A sailing hydrofoil is a wing-like structure on a sailboat that provides a speed advantage over more traditional boat designs. The sailing hydrofoil actually lifts most of the hull, or even the entire hull, out of the water, which greatly reduces the drag as it goes through the water. The concept is more than 100 years old, and enabled man to break some speed records. Some boats may be able to be retrofitted with hydrofoils.
Most types of boats can accommodate hydrofoils, and sailboats are no different. The sailing hydrofoil could be a single hull, often referred to as a mono hull, a catamaran, or a trimaran. A catamaran is a sailing vessel with two hulls and a trimaran has three hulls. Those hulls are held together by a single upper deck. The wider the ship, the more stable the sailing hydrofoil is.
The sailing hydrofoil works with its wing-like appendage. Just like a wing on an aircraft provides lift, a hydrofoil in the water accomplishes the same thing. The main difference is that a hydrofoil does not need to be as large as an airplane wing, because the water is much more dense than air.
One of the main claims of the sailing hydrofoil is that it can travel faster than the wind speed that it is powered by. As implausible as it seems, that is actually true. The hydrofoils can lift the sailboat to such a level that the hydrofoils themselves are almost out of the water. As this is happening, the wind that is flowing over the sails provides thrust for the boat, thus taking the place of some of the wind that was originally responsible for propulsion.
While the most commonly seen sailing hydrofoils are those that are meant for one or two people, larger models also exist. The smaller models are typically used for recreational use and racing competitions. Larger boats may actually have stacked hydrofoils, which provide even more of a lift. This allows for even greater speeds as the boat's hull is lifted out of the water.
The concept of a sailboat using hydrofoils is nothing new. The first hydrofoil ideas were developed by William E. Meacham in 1906. Two years later, Alexander Graham Bell began to test the idea in real-world applications. By 1920, hydrofoils had reached speeds of 119 miles per hour (191.5 kilometers per hour). Since then, the concept as even been applied to motorboats to help reduce drag and increase fuel efficiency.