Joe wrote:
The oragami boat here used the rudder skeg as a keel cooler.


That is a good idea, but you don't even need to do that.
Just run parallel cooling lines (small diameter tubing works
best, but you have to make sure they will carry enough flow)
in metal-to-metal contact with the hull. The entire hull
will dissipate the heat.


Has 25 gallons of antifreeze in the rudder skeg, just wonder if the
antifreeze is a good enough rust inhibitor

Aluminum doesn't rust. Doesn't need an inhibitor.


... if the keel skeg will
radiate the heat well enough. If so... it sure beats the hell out of
having cooling channels or pipes coming out of the hull.


That's for boats made of wood or foam core or some other
insulator.

Another clever idea for a heat sink is to put a coil in each
thru-hull. Some refrigeration units have these as an option,
gets similar efficiency to water-cooling but you don't need
a pump.

DSK