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Old 19-02-2009, 18:45   #1
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Join Date: Feb 2009
Location: Brisbane, Oz
Boat: Roberts 36 - Clarity
Posts: 24
Keel cooling

I must bite the bullet and replace the BMC Commander 53 horse auxiliary diesel in my Roberts 36 "Clarity". Would members with more engineering knowledge than me advise why I wouldn't consider using, say, a good secondhand 2 litre diesel (Toyota, Nissan, Mitsubishi) and a keel cooling unit (eg Fernstrum Gridcooler). I would need to have built a stainless water jacket for the exhaust, to be included in the overall cooling system, and provide substantial thermal lagging to the run of dry exhaust. In Oz, we have a plentiful supply of late model, low hours, secondhand diesels from Japan, courtesy of their stringent antipollution laws. Say $AUD4k for the engine and exhaust jacket, the cost of the keel cooler, and a control panel consisting of orignial guages stacks up against, say, $AUD17k for a comparable Nanni, or $AUD20k for Yanmar is rather appealing. I run a bilge blower whenever the engine is running. Perhaps this could be ducted along the run of dry exhaust as well? Cheers in advance. Bill
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Old 19-02-2009, 19:54   #2
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Join Date: Nov 2006
Location: Vancouver, Can.
Boat: Woods 40' catamaran
Posts: 277
Don't forget the cost of:

- flexible mounts
- a bell housing might be needed to match to a suitable gearbox
- damper plate
- a gearbox $3K AUD?
- keel cooler maybe $500 - 1K

Lots of extra drag with a keel cooler as well.

Do you have a dry exhaust right now? If not it would be pretty hard to build into a sailboat without adding a LOT of extra heat into the boat. Typical diesels reject about the same amount of heat into the exhaust as they put out. So you might be adding 10 or 20 kW of heat into the inside of the boat. Even with lots of lagging, diesel dry exhausts give off so much heat that you can feel the radiant heat from a few inches away with a bare hand.

Welcome to Lancing Marine, the boat builder's source of engines and marinising parts is the best source of marinizing info I know of. They sell lots of parts that might help you out. Not trying to discourage you too much, but the savings might be less than you think.
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Old 20-02-2009, 16:18   #3
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Boat: Custom cutter, 42'
Posts: 702
The details are important. Does the engine have a bellhousing that can mate up to the gearbox you'll use? (Adapter plates are frequently available, or you can make one yourself). What will you need to do to drive the accessories you need? (is the flywheel pulley OK, or will you need something different?) Where will you mount the accessories?

That said, using an engine as you describe can save a lot of money. Keel cooling, if it is done properly, is much more reliable than the common raw water pump/heat exchanger set up. It eliminates many potential failure modes.

I'll have to disagree with Evan about dry exhausts having to give off lots of heat. If they do, by definition, they aren't well insulated. It is possible to insulate dry exhausts so that they give off little heat. Traditional lagging is not a very good insulator. Rockwool has a much better insulation rating.

You have a metal boat. The best way to keel cool a metal boat is use the hull, or appendages like the keel or rudder skeg as the heat exchanger. This is easy to do when building the hull. If you can find a way to run your heat exchanging this way you can eliminate the external keel cooler unit and have a really bulletproof set up.

Regards, Paul
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Old 22-02-2009, 21:51   #4
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Location: Brisbane, Oz
Boat: Roberts 36 - Clarity
Posts: 24
keel cooling

Thankyou, Gentlemen
A bit more research is called for. I appreciate your input
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