I heard some discussion at an IBEX conference that the small block type keel coolers currently being offered by a couple of manufacturers have some serious drawback to achieving their potential effeciencies. The biggest is that the inlet and outlet are physically close together and thermally connected by the metal. This allows the hot refrigerant to transfer a portion of its heat directly to the cool side return. The next has to do with water flow over the surfaces. Underway, performance is great as the boat's motion assures a steady flow of water over the surfaces. But the most important test is at anchor or dock which usually is most of the time. Here the small size of the unit and the "relatively small" amount of heat being disipated is not enough to set up a rising thermal current. Finally, since they mount flat to the hull, nearly half of the potential surface area receives no contact with the water. I'd like to see a small tubular type like a Fernstrum offered for this application. I use a Fernstrum for my main engine and it is a quality product with excellent flow around rectangular cupronickel tubes. They are a little pricey, but maybe similar design in a small size would be feasible. Does anyone use a small Fernstrum for refrigeration? Or just run some copper tubing down one side of the keel and back? Dan Gill dd44 "Pelagic"