The raw water pump on an inboard engine is usually a Jabsco or similar flexible impeller pump, driven by the engine. In a service you replace the impeller, the oil lip seal and the mechanical water seal.

In this video I pull Renko's Jabsco raw water pump apart to work out how it goes together, and replace everything that needs replacing. After that I go for a short SCUBA dive to check where the propeller sits relative to the rudder and cutless bearing.