What naval diesel engines burn

Do naval diesels use road diesel or bunker fuel?

They can use heavy bunker-like fuel; the term describes the diesel cycle rather than a particular road fuel.

The word diesel identifies the engine's operating cycle rather than a single retail fuel grade. A large marine engine need not burn the same refined product placed in a road vehicle. It can use a heavier, bunker-like fuel while retaining the defining diesel-cycle machinery. Separating fuel from engine type avoids importing automotive assumptions into naval engineering.