Cavitation is a fluid dynamics phenomenon in which the pressure in a flowing liquid drops locally below its vapor pressure, causing the liquid to vaporize and generate countless bubbles.
As a hydrofoil wing or fin travels through water at high speeds, the pressure drops rapidly on the surfaces where flow velocity increases (primarily the upper side, which becomes the negative pressure zone) according to Bernoulli’s principle. When this pressure drops beyond a certain limit, the water effectively boils even at room temperature, generating fine water vapor bubbles. This is the basic principle of cavitation.
In kitesurfing, the impact varies depending on the board style. For twintip boards, the heel-side rail provides most of the lift and resistance needed to ride upwind, making the role of the fins relatively limited, so cavitation rarely becomes a serious issue. However, for old-school course racing boards or hydrofoils, the underwater fins and wings themselves generate significant lift and drag, making hydrodynamic changes on their surfaces extremely critical.
When a foil reaches a certain speed (typically around 35 to 50 knots) and cavitation occurs, the wing surface becomes covered by a layer of bubbles instead of water. This causes the fluid layer to separate, resulting in a sudden loss of lift and a massive spike in drag. Consequently, the rider risks sudden stalling or spinning out at extreme speeds, leading to severe crashes.
Furthermore, when the generated bubbles collapse instantaneously due to the surrounding water pressure, extremely strong shockwaves are produced. Over time, this continuous impact can accumulate microscopic damage (erosion) on the surface, even on robust foil materials like carbon. In cutting-edge foil design pushing the limits of speed, overcoming the cavitation barrier—such as by adjusting profile thickness—remains the greatest technical challenge.
* Unlike ventilation, which involves drawing air from the water surface, cavitation is caused purely by a pressure drop due to speed.
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