Hydrofoil

An underwater lifting surface shaped to generate hydrodynamic lift as it moves through water.

A vessel may use one or more foils to support part or nearly all of its weight, reducing immersed hull area and wave-making resistance at sufficient speed. Foils may be surface-piercing or fully submerged and can be fixed, actively controlled or integrated with rudders, centreboards and propulsion units.

Lift, drag, stability and ventilation or cavitation depend on foil shape, angle, depth, speed and control. Foils impose substantial structural loads and add underwater draft and impact risk; not every hydrofoil vessel completely raises its hull clear of the water.