hydrofoil

A hydrofoil is a specialized vessel equipped with underwater wing-like structures, called foils, designed to lift the hull out of the water during motion. By raising the hull, the craft minimizes "wetted surface area," which drastically reduces hydrodynamic drag—the resistance water exerts against a moving object. This allows the hydrofoil to achieve significantly higher speeds and greater fuel efficiency than conventional displacement hulls. Think of it as an airplane taking off; the physics are nearly identical, but the medium is water instead of air.

The concept dates back to the late 19th century, with pioneers such as Alexander Graham Bell experimenting with early designs. Those first models were often unstable and difficult to control, but modern computerized flight-control systems have refined the technology, making today's hydrofoils smoother, more stable, and highly efficient even in rougher seas.

Today, hydrofoils serve a variety of roles. Many regions use them as passenger ferries for quick travel across bays and channels. The military has used them for fast attack craft and patrol boats where speed and maneuverability matter. In recent years, the technology has also become popular in sports, including foil surfing, kiteboarding, and the high-tech yachts of the America's Cup. In some contexts, "hydrofoil" can also mean the underwater wing itself rather than the whole vessel, but in most conversations it refers to the sleek, "flying" boat.