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post #1 of 4 Old 08-26-2013 Thread Starter
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Exhaust Flap

I have a typical external rubber flapper on my exhaust exit. These things do not form a very effective seal. Although I have never had it happen, it seems that during a long run under sail alone with a following sea, that water could possibly get into the exhaust system. Even though there is a good rise above the level of the exit point in the rubber exhaust hose, I have wondered whether repeated waves breaking under the stern could eventually get up over the rise and down into the muffler/riser/engine. Has anyone ever heard of this happening? Has anyone seen a better mouse trap for a 2" exhaust?

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post #2 of 4 Old 08-26-2013
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Re: Exhaust Flap

I've not, personally, ever heard of that happening. It seems the exhaust flap on most yachts is simply there for peace of mind (..and banging at anchorages to annoy the neighbours).

As you say, given a proper rise then down to the muffler very little water should get into the system even if the exhaust outlet itself was under water. Even if water managed to get over the rise, the muffler is designed to get water in it in normal operation anyway and, if properly sized and spec'd, said water will be blown back out the moment the engine starts..

I really don't think you have a problem.

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post #3 of 4 Old 08-26-2013
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Re: Exhaust Flap

Any water in the exaust hose can easily hydraulic up and over the hump and fill the engine while sailing with a following sea.Flopper valves are not effective in the real world. I think a rv type black water dagger board type valve at the transom is good insurance ( push/pull from cockpit is easy). My muffler has a valve on the bottom that opens when the engine is off (oil pressure controlled) I've crewed on several boats that filled their engines offshore, ;once off Cape Conception in the really rough and the only tool on board was a crescent wrench. This was the same trip where the skipper spent 3 days hidden in a fetal position , but that's another story
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post #4 of 4 Old 08-27-2013 Thread Starter
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Re: Exhaust Flap

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Originally Posted by Capt Len View Post
Any water in the exaust hose can easily hydraulic up and over the hump and fill the engine while sailing with a following sea.Flopper valves are not effective in the real world. I think a rv type black water dagger board type valve at the transom is good insurance ( push/pull from cockpit is easy). My muffler has a valve on the bottom that opens when the engine is off (oil pressure controlled) I've crewed on several boats that filled their engines offshore, ;once off Cape Conception in the really rough and the only tool on board was a crescent wrench. This was the same trip where the skipper spent 3 days hidden in a fetal position , but that's another story
The only thing that bothers me about any kind of permanent valve is that if mistakenly left closed, the engine would probably blow something apart if inadvertently started. I bought a 2" PVC ball valve which would go into the exhaust hose nicely but have been reluctant to install it for that reason. I guess anything that makes a tight seal would create too much back pressure. Maybe just a simple tapered plug, something disposable, possibly hard foam that could be jammed in the hole when making long passages would work. The engine would just blow it out when started. It could even be attached with a piece of small line to retrieve.

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