Flexible bellows exhaust connection - SailNet Community

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  #1  
Old 11-15-2007
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Flexible bellows exhaust connection

I have gotten along fine for 45 years in my wood sailboat with a rigid metal exhaust, water jacketed to the riser, with the cooling water discharging into the pipe after the riser. Never had a problem with water getting back to the engine. My old gas engine was mounted solid to the beds.

I'm planning to repower with a diesel (Yanmar 3YM30) that will be on flexible mounts with a lot of rock and roll. I'd prefer to replicate my tried and true system with the diesel, but only if I can come up with a reliable flexible metal coupling from the exhaust manifold to the rigid pipe. Anyone know of a source for such a coupling that can tolerate all this shake?

I know that modern wet exhausts with water lift mufflers are "Cool and Quiet and trouble free." And they don't require a flexible metal coupling. However space limitations in my boat present a problem for this type of system.
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Old 11-15-2007
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Same set up on my boat

I have a very similar situation on my boat. It's got a fiberglass hull, but that's not the issue, right? I have a diesel Universal M4-30 on flexible motor mounts. My set up goes from the exhaust manifold via a threaded fitting to a water-jacket exhaust tube. The hot (now somewhat cooled) exhaust gas continues through a rigid, albeit circuitous, route of 2" OD black-iron pipe. It eventually rejoins the water which exited the water-jacket just before leaving the boat through a through-hull located above the waterline under the aft overhang.

Most of my piping is hung from hangers, like on a car's muffler exhaust system, so it takes the engine movement without a lot of noise and vibration...and without self-destructing. The first leg is a long run, so most of the vibration is absorbed before it goes anywhere tight.

You might think the black-iron would break down quickly in the salt air, but the last one lasted 10 years before giving up.

I hope you get a better answer than this one, because I'd like to do something more elegant as well. I know there are new rubberized hose and elbow materials out there, but I'm unsure if their temp ratings could take the heat in a worst-case scenario - even with the exhaust gas being cooled somewhat via the water jacket.

I considered the flexible stainless steel exhaust materials I've seen on many 18-wheelers, but couldn't find any in my desired OD. I also wondered if their safe enough (air tight) for this application.

Any thoughts out there on that?
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Old 11-16-2007
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Quote:
Originally Posted by Pub911 View Post

I considered the flexible stainless steel exhaust materials I've seen on many 18-wheelers, but couldn't find any in my desired OD. I also wondered if their safe enough (air tight) for this application.

Any thoughts out there on that?
That's avail. in any size from 1" I.D. (not O.D.), and up. The O.D. type usually has welded pipes on the ends for specialized apps..

Try a lg. automotive or truck parts supplier, they can get it and many have it in stock.
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Old 11-16-2007
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Maybe a flex coupling for automotive use, it is to be dry at this point right ?
http://www.jegs.com/webapp/wcs/store...31438_-1_10263
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Old 11-16-2007
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Trident Marine makes various sizes of "hump hoses" that allow some flexibility for an engine exhaust....

http://www.tridentmarine.com/stage/wetex_elbows.htm
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Thanks for the info on the ss flexhose. Does anyone know if it's safe - airtight, that is, or any other risks for this application (sorry to steal the line of questions by the way, but figured this might help you too).
And regarding trident, I know they rate the humphose and all their hoses to pretty high temps...400F if memory serves....but will this set up get hotter than that? Recall, the exhaust gas has been cooled somewhat by the water jacket upstream. But I've always wondered under extreme conditions, if the exhaust would get hotter than that.
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Old 11-17-2007
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More thoughts on metallic bellows exhaust

My original post in this thread was my first experience with SailNet. Thanks to all you rapid responders. I also want to apologize to Junior Member "fishstick" for the unintentional near-appropriation of his name. I have had something to do with manufacturing this beloved food, though. I even recall when, years ago, we made them with 75% haddock and 25% breading.

I heard from SloopTattoo (thank you) that he has had good luck with an inexpensive stock automotive bellows. Meanwhile I've queried a custom bellows manufacturer I found with Google. The Yanmar I'll be installing is really shaky and will impose a high lateral cycling load at the manifold connection. I can use up to about 18" of bellows to limit the stress. The exhaust system for this repower is going to be one of the more challenging aspects of the whole project.
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Last edited by FishSticks; 11-18-2007 at 07:54 AM.
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Old 11-17-2007
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Someone could probably answer better about the hump hose, but on my Catalina 30 with a Universal M25 diesel, the hump hose connects the exhaust riser to the aqualift muffler, after the point that water is injected into the exhaust. This is pretty standard, I believe.

Also, after the muffler, all the exhaust plumbing is exhaust hose.
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