Mopar Marine Pick
Isn't there something about marine engines and rotation???
Do they turn opposite of cars???
Only one side. With two right hand rotation engines, the boat will not track straight.
Aircraft twins generally have one left hand engine and one right hand engine. This keeps them straight and level. This is a factor of the prop radius and pushing up or down farther out.
How do you know a right or left hand engine for the definition? If you are looking at the flywheel end with your fists like you are gripping the flywheel and your thumbs pointing up. If your right hand thumb is pointing in the direction of rotation of the flywheel, it is a right hand rotation engine. All automotive are this way, unless Smoky Yunick raced it. :-). If the left thumb points in the direction of rotation, it is a left hand rotation.
For oilfield use, many Detroit Diesel installations used "twin sets", with two left hand engines bolted to a gear box with two overcenter clutches. The gearbox had three gears with the center gear rotating right hand. This provided redundency. If an engine had a problem, the clutch could be locked out and the engine worked on.
They also used twin and quad units for marine applications. Quad 16V71 units could be used and two quads used in bigger ships. One would have the engine locations changed to get one right hand prop and one left hand prop. A quad unit would have two right hand engines and two left hand engines. The outer gears would have a clutch on the front and back sides, with generally the left hand engines on the front and right hand engines mounted backwards on the back. Governors and throttle linkages had to exactly match so all engines pulled the same load. Otherwise on engine could be doing most of the work and another going for a free ride.