[Euro Cruiser]

Wolfgag:

The short answer to your Q is 'No'. In fact, at one point on a previous boat - I've used this method on several - we got down to 1-2 gals of water in our keel tank yet fridge performance was not effected.

While in Trinidad, an 'engineer' on a Tayana 43 who was dissatisfied with his raw water cooling arrangement (he had two reefer systems) wanted to switch to fresh water but, like you, wondered about the system efficiency once the water volume in a source tank decreased. He sourced a 5 gal bucket of fresh water(which sat in his cockpit in the blistering sun) temporarily to measure the temp increase of the water and the most he could get it up was 5F. After a week's 'experiment', he shifted over to FW tanks sourcing both units.

The reason the water doesn't heat up is the huge heat transfer that occurs as your boat floats in an ambient medium (sea water temp) and all the materials between your fresh water supply and that ocean medium are sucking off the heat that is absorbed. To the extent your water tank(s) contact the hull's surface, this 'heat loss' will be greater; to the extent they are surrounded by air (800X less dense than water) the heat transfer will be slower.

Talbot, I wasn't commenting on the electrical performance of any given system; my points have been that using raw water as a cooling medium can be improved on, and the purchase of special thru-hulls or keel coolers seems an unnecessary expense. Just my opinion, of course.

Jack