Main propulsion engine units are directly connected to the propeller shafts and are designed to provide a marine vessel with forward motion. Auxiliary engines are smaller, secondary engines that can be connected to power generators to provide power to a vessel’s lighting, electronics, and HVAC systems. Engine cooling systems utilize liquid coolants or thermal oils circulating through heat transfer pipes routed through the engines. Once the coolant or oil has passed through the engine, it is routed through seawater tanks for further heat transfer.