flat or curved finlike device, attached by struts to the hull of a watercraft, that lifts the moving watercraft above the water's surface. The term is often extended to include the vessel itself. Like an aircraft wing in its appearance and function, the foil develops lift as it passes through the water; the hull is raised above the surface, and the drag caused by the vessel's contact with the water is thereby reduced. Hydrofoil vessels are capable of traveling faster than 70 mi (113 km) per hr. They are used for ferries in many countries in Europe and Asia; in the United States they are used mostly for military purposes. In addition to offering greater speeds, such vessels do not pitch and roll as do conventional watercraft. Foils may be of the submerged or the surface-piercing type. On oceangoing passenger ships a type of hydrofoil called a stabilizer is used to minimize wave action on the vessel. The first hydrofoil vessel was built in 1905 by the Italian engineer Enrico Forlanini. In 1918, Alexander Graham Bell built the HD-4, a vessel 60 ft (18.3 m) long that attained a speed of 70.86 mi (114.03 km) per hr.
See C. Hook, Hydrofoils (1967); R. McLeary, Jane's Surface Skimmers (annually, 1968–); W. T. Gunston, Hydrofoils and Hovercraft (1969).
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