A cavitation plate, also known as an anti-cavitation plate or a cavitation plate fin, is a component typically found on the lower unit of an outboard motor or sterndrive. It is a flat, horizontal plate that extends horizontally from the lower unit, often just above the propeller.
The primary purpose of a cavitation plate is to improve the performance and handling of the boat by reducing cavitation and improving water flow around the propeller. Cavitation occurs when the pressure on one side of the propeller becomes too low, causing water to vaporize and form small air bubbles. This can lead to a loss of efficiency, reduced propulsion, and increased propeller noise.
The cavitation plate helps mitigate cavitation by redirecting water flow and creating a barrier between the propeller and the water surface. It can increase water pressure on the propeller blades, enhancing traction and reducing the risk of cavitation.
See also: trolling plate, boat hydrofoil