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Old 07-16-2016, 02:19 PM   #1
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Main engine and genset exhaust through one muffler

Is it practical to route both the prime mover and the genset exhausts through a single mufflers? With a low back pressure muffler and the venturi effect I don't see how main engine exhaust would be blown through a non-operating genset.
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Old 07-16-2016, 02:25 PM   #2
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No. Several reasons make it a bad idea.
If the valves are on overlap. You can have exhaust gases to push back through the main engine and out the air cleaner. Also if the engine has a turbo it will spin it with no oil and that will cause premature failure of the bearings.
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Old 07-16-2016, 02:42 PM   #3
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This is not permitted by ABYC standards for the reasons Big Cat mentioned. I was an expert witness in wrongful death case where the boat builder combined the two exhausts and it killed someone. The builder lost.
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Old 07-16-2016, 02:57 PM   #4
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Yep, bad idea.

There are some sporties that do this, but if you look closely, the gen exhaust ties into the main exhaust right at the tailpipe exit and has a clamshell glassed in to keep the two flows separate. I still don't like those, but less risky. I think this system is responsible for some of the otherwise "unexplainable" water in genny engine events.

Run the exhausts separate.
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Old 07-16-2016, 03:03 PM   #5
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Most modern sportsfish are built this way as are a number of large yachts. This meets the ABYC requirement because each exhaust terminates at the exterior surface of the hull.
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Old 07-16-2016, 04:29 PM   #6
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Good to keep the transom clean with only the main engine exhaust hole, bad for the megaphone effect from dumping 2.5" gen exhaust into a 14" main engine exhaust pipe just before the transom.




Quote:
Originally Posted by Ski in NC View Post
Yep, bad idea.

There are some sporties that do this, but if you look closely, the gen exhaust ties into the main exhaust right at the tailpipe exit and has a clamshell glassed in to keep the two flows separate. I still don't like those, but less risky. I think this system is responsible for some of the otherwise "unexplainable" water in genny engine events.

Run the exhausts separate.
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Old 07-17-2016, 07:42 AM   #7
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Quote:
Originally Posted by Ski in NC View Post
Yep, bad idea.

There are some sporties that do this, but if you look closely, the gen exhaust ties into the main exhaust right at the tailpipe exit and has a clamshell glassed in to keep the two flows separate.
True on the big and medium Bertrams of my acquaintance. Worth bearing in mind that the genset(s) usually have water-lift mufflers which may prevent backflow.
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Old 07-17-2016, 11:08 AM   #8
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Water lift mufflers may reduce the chance of backflow, but once you fill one of those little coffee cans up the water will start heading towards the exhaust manifold / turbo

A separator would make it next to impossible to back flood



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True on the big and medium Bertrams of my acquaintance. Worth bearing in mind that the genset(s) usually have water-lift mufflers which may prevent backflow.
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