The ship’s main engine produces power to propel a mega-ship at sea. The power is generated inside the cylinder liner, where the fuel is compressed and burnt.
The power produced inside the cylinder is then transferred to the propeller via connecting rod and crankshaft.
No engine is 100% efficient and the ship engine will also have some waste energy while doing this work. This waste energy will be in the form of heat and exhaust.
The heat of the engine is taken care of by the jacket cooling...
https://www.marineinsight.com/videos/watch-ships-main-engine-exhaust-valve-working/