Hydrofoils use underwater wings to generate lift, allowing them to sail without touching the water at high speeds. Alexander Graham Bell built the first successful hydrofoil in 1919, and modern hydrofoils have submerged foils for stability. Commercial hydrofoil routes were established in 1952, and they are still used in various countries today.
A hydrofoil, not to be confused with a hovercraft, is a vessel that uses its underwater wings to generate lift in the same way that an aircraft uses its wings to generate lift in the air. Foil is another word for wing. A foil generates a region of negative pressure immediately above it, producing lift. This lift elevates the hull off the surface of the water, supporting it on vertical struts attached to the plates below.
When the hydrofoil reaches a critical speed, the entire hull body sails without touching the water. When the hull is suspended, the engine does not need to consume much energy to overcome water resistance. The foils are the only part of the vessel that continues to produce drag in the water. Because they literally fly across the water, hydrofoils are capable of high speeds, having set world records for both conventional and human-powered navigation.
A hydrofoil held the world water speed record between 1919 and 1929. Interestingly, this hydrofoil was built by telephone inventor Alexander Graham Bell in 1908, after he became interested in hydrofoils. Bell and his collaborator Casey Baldwin had seen the first popular article on hydrofoils in a 1906 Scientific American article by William E. Meacham and were inspired to build one. In 1919 they were very successful and built a vessel that reached a top speed of 70.86 mph (114 km/h) thanks to engines supplied to them by the United States Navy.
The first hydrofoils had U-shaped foils, called surface-piercing foils, that essentially jumped on the surface of the water. In modern hydrofoils, the foils are completely submerged, making the vessel less susceptible to surface turbulence. The downside is that there is no uniform layer of surface tension to ride on, so advanced computer control systems must continually update roll, pitch and yaw to keep the craft stable. Layered foils, in a style similar to those of a biplane, are sometimes used for the purpose of providing a smoother ride.
Only in 1952 was a commercial hydrofoil route opened. Baron von Schertel, a German hydrofoil pioneer, was active in the area before and during World War II. After World War II, he fled to Switzerland, where he founded the Supramar company, launched the first commercial hydrofoil route, and went on to design and build dozens of new hydrofoils throughout 1951-1971. The Pegasus-class hydrofoils served in the United States Navy between 1977 and 1993, where they were used to crack down on narcotics trafficking. Today, hydrofoils are still used in China, the United States, Greece, Japan and Russia, among other countries.
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