Keel cooler

A keel cooler is a closed-loop heat exchanger mounted externally on the hull below the waterline that rejects engine cooling-water heat directly to the surrounding sea without taking seawater aboard. Fresh engine coolant circulates through hull-mounted tubes, channels, or a box cooler welded to the shell, and the moving water and the vessel’s forward motion carry the heat away by conduction and convection. It removes the sea-chest, strainer, and seawater-pump train and the fouling and corrosion they bring, which suits tugs, workboats, and ice-class vessels where a flooded seawater intake is a liability.