Hydrofoils

A hydrofoil is a lifting surface or foil attached to a boat or other watercraft that operates underwater. As the vessel gains speed, the foil sections generate lift from the flowing water, raising much of the hull out of the water. This reduces hull wetted area and form drag, allowing higher speeds and a smoother ride at velocity.

Lift is produced by the foil’s shape and angle of attack, governed by fluid dynamics. The crew or on-board systems balance lift, propulsion, and weight so the hull sits steadily above the water. Control surfaces and stabilizing foils help manage pitch, roll, and trim, while some craft use computer-assisted systems to adjust incidences in real time.

Hydrofoils come in different configurations. Fully submerged foils operate entirely below the hull, while surface-piercing foils extend above the water line and re-enter the flow as speed increases. A vessel may use a single central foil or multiple foils arranged to provide lift and stability. Foils are supported by struts or pylons and can be fixed or retractable to ease docking and protection from debris.

History and use have evolved since the early 20th century, with early experiments leading to practical, high-speed craft in later decades. Today hydrofoils are used on some specialized high-speed passenger ferries, racing boats, and military vessels. They offer advantages in speed and ride comfort but entail higher construction and maintenance costs, sensitivity to sea state, and exposure to underwater hazards. Ongoing research explores materials, control systems, and hull-foil integration to improve efficiency and stability further.