In short - hydrodynamic cavitation is caused by the explosion of tiny bubbles created by pressure differentials across the surface/edges of a propeller. The (new) and largest container ship in the world has two propellers (4 blade I think) that cost a million dollars each to pour, cut robotically and X-Ray. Many propeller designs were tank tested to find the best design to reduce propeller "eating" cavitation. You also have anti-cavitation plates on your marine engines that help a bit too. Cavitation also affects skegs etc.