Bowman marine heat exchangers. There are three techniques used for water-cooled marine petrol and diesel engines, which include direct cooling, heat exchanger cooling and keel cooling.
Direct cooling of the cylinders and heads by sea water is unsatisfactory, because the engine which was probably originally designed for radiator cooling will run too cold and the sea water will eventually ruin the cylinder block and heads.
Heat exchanger cooling is the most common method, the sea water being isolated in components which can be designed to withstand its corrosive affect. The closed fresh-water circuit can be thermostatically controlled so that the engine operates at its designed temperature.
Keel cooling is suitable for small boats operating in shallow weedy water, but the need for pipework external to the hull is a severe limitation.
