Finally, after seven weeks of worry, googling and angst, we have our repaired exhaust riser installed in Galapagos. Here is what we finally ended up with.
You will note an eerie similarity to the first riser we had built in Astoria. The only difference is that we have added an eight inch long 2.5 inch wide flexible coupling as close to the exhuast manifold as was possible. The flexible coupling is a bellows type with a smooth liner inside to protect the bellows from exhaust particulates which hopefully will prolong its life. I opted for a larger flex coupling in the hopes that it will provide some additional strength to the whole unit. Sizing the coupling up came at the expense of requiring two stainless cones to fit the coupling to the existing pipe.
All of this is a departure from an earlier design that would have increased the diameter of the exhaust to 2 inches right after the manifold and added a flex coupling horizontally instead of vertically. I still like that idea and may design another system using threaded pipe to allow me to build yet another exhaust riser if this proves unreliable.
So why didn’t I just have the new riser designed like this? Mostly I was talked out of it by the welders who tended to agree that the existing design was actually quite robust in all areas and the only modification needed was the flex coupling to allow for engine movement without stressing the riser. The existing system is quite beefy and at this point I can only hope they are right. Still I would like to have a new manifold flange made with a 1.5 inch NPT fitting welded on that would allow me to create my own riser using easily acquired stainless fittings and pipe. Broomfields, the local exhaust experts in the Puget Sound, has a flex coupling with NPT fittings welded on that would be ideal for such a project.
As you may note, I am not done worrying over this part of our engine. Maybe it will just take some time with this layout to begin to feel that this is a safe and robust system. On Saturday, I added an additional brace to the riser and used what fiber glass heat tape I had left to wrap the majority of the pipe. I ran the engine for an hour at a variety of RPMs and everything looked great. In reality the engine moves very little except at dead idle. At 750 RPM, you can see the coupling moving perhaps a quarter of an inch. Since I know the engine moves most in this range, I tend to bump the speed up a bit as soon as I can and the vibration disappears quickly. Still, boats tend to spend a lot of time at idle, especially during docking maneuvers. When docking, I prefer to worry about crashing into expensive boats and would rather not have to split my time worrying over the engine.
Now that we have a functoning engine again, Let’s hope the weather will allow us to get out on the water a few more times. We are well and fully into fall here but we should have a few days here and there that will allow us enjoy a crisp autumn sail.