Indirect cooling system

An indirect, or central, cooling system cools the engine and auxiliaries with a closed fresh-water loop, and rejects that heat to seawater only in central coolers, so seawater never enters the machinery. Treated fresh water circulates through the engine jackets, lube and charge-air coolers, and auxiliaries, then through plate central coolers cooled by seawater drawn from the sea chest. Keeping seawater out of the engine and out of long pipe runs cuts corrosion, scaling, and erosion to the central coolers alone, and the loop usually splits into high-temperature and low-temperature circuits sharing one expansion tank.