Neoprene impellers and nitrile impellers for boat pumps. The impeller is a vital component of your engine’s cooling system. Boat impellers are often rubber with vanes to draw water to the engine. Most marine engines will have a raw water pump with a flexible impeller. It is used to pump raw water from outside the boat through the engine’s raw water. Find your pump impeller easily, Water Pump Flexible Rubber Impeller Replaces. Changing an impeller on an outboard marine engine is a common practice for do-it-yourself. Shop our huge in stock selection of shafts impellers