Join Date: Oct 2007
Location: Beacon Falls CT USA
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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?