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Old 06-04-2008, 06:31   #1
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Exhaust question

Our recently purchased catamaran has a single inboard engine in the center of the boat (aft view). The exhaust pipe ends about 8 inches below the water line. The engine is above the water line and we hope the boat never heels. In all that we read (Calder, etc.) the illustrations show the exhaust pipe ending above the water line. A local "expert" tells us that having the exhaust below the water line will create undue pressure on the engine and that there is the danger of a following sea causing water to flow up the exhaust pipe thereby flooding the engine. Our exhaust system does not have a muffler. Do we need to make modifications?

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Old 06-04-2008, 09:07   #2
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Is there not a " riser" in the exhaust system, or does the exhust go straight down to the thru hull? there are lots of Prouts out there, I would think it's a good design.
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Old 06-04-2008, 10:08   #3
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A couple inches below the waterline shouldn't hurt. It wouldn't be any worst then a wetlift.

Although, there should be a loop in your exhaust about 18" above the waterline before it exits the vessel. But then you then you would have go with a wetlift just to catch the returning water after a shut down.

Maybe a flapper on your exhaust port, like on powerboats, would be the best solution.

If the boat is heeling with the motor running, water will not enter.

Marine Hardware - 316 SS Generator Exhaust Ports or similar.

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