Of course all damages resulting on an impact like fire, sinking, theft of the engine or its parts and so much more are insurend in the range of the yacht's hull insurance.
Nethertheless there are other risks light damages on the cylinder head gasket, the pistons might cause a problem or the engine is failing completely without an insured event in the range of the yacht's hull insurance.
These claims can be covered by the engine breakdown clause which is securing your engine against any damages in the range of the contract.