Retired Naval Architect
Join Date: May 2012
Location: ON S/V Strider
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Re: Keel cooling
Keel cooling is on the list of things I would like to do with my boat since I have a RW cooled engine. It's the least troublesome form of FW cooling there is.
For a sailboat, you would want to use a "Package Cooler" from Fernstrum or Walters instead of a bunch of pipe looped back and forth. You will be surprised how small it is for 20-30 hp. The boundary layer gets so thick towards the back of a boat that the drag won't be significant with a wedge in front of and behind the cooler.
Dry exhaust isn't practical. You will need to install a second water pump belted off the engine to provide exhaust water. You will also need a small header tank.
Raw water cooled engines like mine have a thermostat set to a temperature that is too low for optimum operation. This is necessary to keep salt deposits from quickly building up. One of the main reasons I would like to convert to keel cooling is to get the engine running hotter as well as being able to make domestic hot water.
Yanmar does not sell a thermostat with a higher setting which will fit my engine so I would need to remove the thermostat and replace it with an external one that would keep all the water in the keel cooler loop at the right temperature. As you can see, there are some design and engine specific issue so a keel cooler conversion should be done with some informed professional help.