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I don't know what percentage of Dry installations on trawler yachts require blowers to cool the stacks, but these industrial-sized 120/240VAC blowers are large, noisy, and relatively expensive. …[/ QUOTE]
I’ve never seen a blower like you describe on a dry stack boat. What is it for?
If for ventilation, it’s a waste of time. Every dry stack I know of has the exhaust pipe inside a larger pipe. The hot exhaust pipe induces a substantial air flow due to rising thermals. Cold air inlets are always directed to the lower areas of the bilge. Hot air rises right out the stack.
Maybe in the tropics?
I can't speak for recent, but Nordhavns had large industrial Delta blowers to exhaust heat from engine room and exaust stack.
George Beuhler originally specified dry exhaust for the Diesel Ducks - it was good for marketing too. When Seahorse built the first steel 38, they could not effectively disappate heat. They tried a number of changes to remediate the issue, then finally just went with wet exhaust out the side of the boat.
Diesel has 135,000 Btu per gallon - over 400,000 Btu if 3-gph. Sure, some goes to energy to move the boat, some gets transferred to a keel cooler, but combustion generates a lot of heat (that's sort of the point of combustion) so somehow all that heat has to be shed - not all of it goes out the stack. Expecting that much heat to passively escape via a fairly small chimney/stack via thermals is unrealistic.
Peter