Posted by peter (18.104.22.168) on July 28, 2004 at 18:09:35:
In Reply to: fumes posted by craig on 14:42:45 06/24/04:
Curious as to what you found was partially blocking your exhaust and how much difference it made when cleared.
The Northern 29 does have a very long exhaust. Probably about 20 feet or so in length. In addition to the length, there are several 90 degree fittings and 1 check valve about half way down the length of the exhaust to keep seawater from backing up the length of the tube. Plus, the head of lift from the waterlift is about 3 feet. All of these add much more backpressure to the exhaust than a regular installation under the companionway stairs. I suspect that this backpressure is the root cause of the exhaust smell, and possibly also keeping the engine and compartment hotter than the regular installation.
With the engine right in the middle of the boat beside the mast there does not seem to be any good solutions though. I saw one where the exhaust was redirected straight out the port side of the boat, right in the middle of the boat about 1 foot off the water. This not only looked ugly, left stains, but just doesn't seem right.
Maybe increasing the exhaust diameter, and trying very hard to eliminate a 90 degree fitting, and possibly removing the check valve might help. But with the engine sitting so low in the boat you have to wonder if sometimes the check valve is needed.
As a comparison, my other boat, with a yanmar under the companionway has about 3 feet of exhast hose, and the actual exhaust exit at the transom is lower than the ehaust manifold on the engine. Almost no backpressure, and all downhill, the complete opposite of the Northern.