Keel coolers are like small radiators attached to the hull in a closed cooling system.

In an open cooling system, the main hull openings for water are for engine cooling and air-conditioner chiller, and a watermaker. In an open system, cool seawater is circulated inside the boat to its machinery.

There are three types of closed system. In the first, a heat exchanger located in the engine room separates the internal water system from the external seawater. In the second, the internal water system is routed through an external keel cooler. Finally, an internal heat exchanger can be combined with an external keel cooler.

Keel coolers are usually made from copper-nickel alloys. They should be flush mounted, to protect them. Stud types are easier to install than threaded types. Some builders put keel coolers in a sea chest.

Channel-type coolers consist of a pipe cut in half and welded the length of the keel in a loop. Additives in the water control corrosion inside the pipe. If there is corrosion inside, the pipe should be thick enough to outlast the hull.

Keel coolers must be connected to the boat’sSecond Common Grounding Point. If not, they should have sacrificial zinc attached.