Being in the Coast Guard, I have seen some of the big ones. A new Hapag Lloyd ship came in from Germany last year. She was 940 feet long and the engine was an in line 10 cylinder 45,000 BHP engine. Valves were the diameter of a basketball and the pistons looked like about 4 ' in diameter. They carried spare valves, two cylinders and two pistons. The prop shaft looked to be about 36" in diameter. She was a two cycle direct drive. That means no "transmission". To go forward, set the lever on forward and air start with compressed air injected into the cylinders to start it turning over. Once it reaches about 20 rpms, fuel is added and it starts. To go in reverse, stop the engine, set lever for reverse and crank. They burn Bunker C which is like tar until heated to 200*F. Max speed on the engine was 300 rpms. Cruise was about 180 rpms turning a 24' prop. The rudder was 90,000 lbs. The flywheel was about 30 tons. She was running twin turbos, each with a turbine housing over 8 feet in diameter. They add lube oil by the 55 gallon drum.