On small passenger vessels which parts of a water-cooled gasoline or diesel engine must be water-jacketed and cooled?

Correct Answer: Option D — All of the above

46 CFR Subchapter T requires that all surfaces of a water-cooled engine, including the block, head, and exhaust manifold, be jacketed to prevent excessive heat radiation. This design minimizes fire hazards in the engine compartment by ensuring external surface temperatures remain within safe operational limits for small passenger vessels.