The issue I believe in putting the keel cooler
in the tank is one of thermal capacity of the tank. The heat has to be radiated back out into the air. If there is sufficient circulation about the tank, then you will reach equalibrium with the air and have a great... ie, air cooled system.
I have given this issue a reasonable amount of thought. I have observed how much heat is displaced into the keel
coolers. It is significant. If it were say 200 watts of heat (don't know the BTU equivilant) I know you can eventually have issues with heat build up in the tank. Eventually, you'll reach ambient air temp between the water and air. Unless you would have to put your compressor
in your engine
space and were worried about heat buildup in that space, the only benefit you get is in having a bigger radiating surface to disipate the heat. But, eventually it would not be much of a differential between a good air cooled system.
The benefit of placing that heat in the ocean is the amount of time it would take to heat up the ocean. You can't put enough energy into the system without it being able to disipate that energy.
I'd also be concerned with leaks
into my fresh water supply. I have to change a zinc in my keel
cooler every 4-5 months. One of the two is about half erroded at that point. There would probably be less errosion, because your not in a very strong electrolytic solution. But if you have any impurities in the water, you'll have want to have some kind of sacrificial zinc in the water. I would not want the refrigerant leaking into my drinking water
. Heck, I wouldn't even want the zinc leaching into my water.
The keel cooler is not a through hull
per se. It is a hole in the boat that has been resealed. No water is coming back into the boat. I put mine behind my keel. No very likely to be ripped off by some kind of accident
I have a Frigoboat keel cooler system, I can't recommend them (enumerated in other posts). But, Richard kohlman has an excellent site for marine refrigeration
. I suggest that, and his book as the first level of research
. I don't remember the site off hand, but you can do a search on this site to find it.