VENTILATION hydrodynamic:

Any system of hydrodynamic profiles moving near the surface tends to suffer from air entrainment. This phenomenon is usually called ventilation.

The VENTILATION hydrodynamic follows that the hydrodynamic pressure over the profile is significantly below atmospheric pressure, so that if the air finds a passage he is immediately drawn into the area of the upper.

The result is a sudden loss of the profile lift force . If the air supply is limited, or if it is drawn only during a short period of time, a simple transient bubble forms on the dorsal surface of the profile and is evacuated in the aftermath.

A much more serious situation occurs when air can enter without interruption. This has often been a problem in the development of hydrofoils mounted on a hollow base, including systems for varying the incidence tends to provide a path for air.

In all profiles evolving near surface, air can leak in down, one solution is to install dams.

The problems of VENTILATION hydrodynamic can be found in the pumping with the suction is too close to the surface .