Here is a pic from our service department of a damaged water pump impeller.  Just a reminder for boaters to get them checked if your engine is not pumping water well.

An impeller is one of the smallest parts on a boat but it is one of the most vital and it can fail at any time, usually without notice. It can also do substantial damage to other pieces of equipment; in some cases, totally incapacitating the engine.

An impeller is a rotating component of a centrifugal pump, which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. Impellers are usually short cylinders with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid radially, and a splined, keyed or threaded bore to accept a drive-shaft.