Originally Posted by Faster
I believe many deep sea freighters still do this...
Correct. The most common propulsion plant for large ocean going ships is the slow speed diesel. Engine is coupled directly to the propulsion shaft and propeller turns at the engine RPM. Reversing is done by stopping the engine, shifting the camshaft, and restarting in reverse. Some of the largest are inline 12-cylinder engines with a bore of around 1 meter and run below 100 RPM.