Ok, I've wrapped my head around this much. It's a fiberglass hull, 30 feet. Engine is a 4BT3.9 Cummins. I think it is rated at 105 HP. The fresh water cooling hose to the heat exchanger is about 2 or 3 inch dia. (guess). I'm thinking Type K refrigeration hard copper tubing in some dia. times number of runs to equal the cooling hose volume capacity (lets say seven to ten sq inches) with the necessary amount of surface area (length of the ten tubes or multiples of) to transfer some unknown amount of heat generated to produce 105 HP at some unknown temp.at some unknown transfer rate, into ambient water at possibly 95 degree temp.( might go to Ft. Lauderdale in the summer), So, given these unknowns, can some engineer out there fill in the blanks to figure out the dia. and length and quantity of tubing? I'm pretty sure a single or double run of tubing would not be enough coolant flow, and don't have a clue how long it would have to be to lose that heat. I have to imagine that the shrimpers have some formula that they've worked out by trial and error that works. Or should I hook up a bunch of tubing and throw it overboard and see if it overheats and work from there? Thanks, Ed

sealubber7@aol.com writes: >with the necessary amount of surface area (length of the ten tubes or >multiples of) to transfer some unknown amount of heat generated to produce 10 >5 >HP at some unknown temp.at some unknown transfer rate, into ambient water at >possibly 95 degree temp.( might go to Ft. Lauderdale in the summer), So, give >n >these unknowns, can some engineer out there fill in the blanks to figure out >the dia. and length and quantity of tubing? You need to do two things: 1) Find out how much waste heat the engine generates. You should be able to f ind this online, usually specified as "Heat rejection to coolant" and express ed in BTU per minute. For example take a look at the Lugger specs: http://www .lugger.com/PDFs/brochure_pdfs/L1066_series.pdf 2) Then use that to size the keel cooler. Here's the form from Walter: http://www.waltergear.com/kcdata.htm Scott Welch Chief Evangelist, Open Text Social Media Group www.opentext.com 905 762 6101 "Things turn out best for people who make the best of the way things turn out ." - John Wooden