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Old 05-19-2019, 11:41 AM   #1
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Stinky Exhaust

I have a dry exhaust and it exits the pilothouse roof at head level when standing on the back deck. There is ventilation around the pipe where it exits, see photo. I rebuilt the system using galvanized plumbing pipe, (1.25" and 1.5") which was a mistake. The first sea trials with the new system I got a lot of smoke, which was the galvanizing burning off, coming up through the ventilation portion. The smoke gradually went away but I still get a bad smell and it is bad enough to make standing at the rear steering station uncomfortable. The exhaust itself is released higher up and directed up and away. The smell is different than diesel engine exhaust, maybe acrid is a good term. Perhaps it takes a long time for all the zinc to go away and yes I know that the vapor is harmful. I am going to investigate for exhaust leaks and am considering replacing everything with plain steel or stainless. The second photo shows the interior with out the cowling. The reason for all the fittings is that the muffler has BSPT ports so had to convert to NPT.

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Old 05-19-2019, 11:47 AM   #2
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Looks like a leak in the pipe judging by how black it is. I would also wrap that pipe in insulation as you might set yourself on fire. Galvanized pipe is ok, but plumbing pipe is very thick; stainless is better. Only 1.5”? What engine do you have? Mine is a Cummins 6CTA and it has a 6” pipe for a stack and the muffler is 5”. Make sure your back pressure is not too high.
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Old 05-19-2019, 11:56 AM   #3
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Quote:
Originally Posted by Xsbank View Post
Looks like a leak in the pipe judging by how black it is. I would also wrap that pipe in insulation as you might set yourself on fire. Galvanized pipe is ok, but plumbing pipe is very thick; stainless is better. Only 1.5? What engine do you have? Mine is a Cummins 6CTA and it has a 6 pipe for a stack and the muffler is 5. Make sure your back pressure is not too high.
That was quick reply. I added a second photo that shows some insulation, and I do now have more on the exposed section. My engine is small, 27hp. I am going to look for leaks.
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Old 05-19-2019, 01:29 PM   #4
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Be careful of flu like symptoms. An early sign of zinc oxide poisoning. It starts with a headache and nausea. I've welded a lot of galvanized metal and the fumes have to be well ventilated. The fumes can kill you.
When steel is galvanized, it makes a chemical bond with the base metal. This results in pure zinc on the outside layer and interior layers having various compositions of zinc and the steel until you get to the base metal. When you slowly cook the zinc off with exhaust temps, it appears to be gone, but the mixed layers keep their zinc a long time. It could take months for all the zinc to burn off. And the zinc on the pipe inside makes the exhaust more toxic.
I'd do it in stainless.
In fishing boats, some made double wall 316 and circulated sea water to keep the cabin cooler and quieter than insulation alone does. Some keep the water under vacuum and have a evaporator making fresh water. Water boils at a lower temp under vacuum.
Also if the trunk with the exhaust pipe is the source for incoming air to the engine, cooler air makes the engine more efficient.



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Old 05-20-2019, 06:38 AM   #5
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. "I rebuilt the system using galvanized plumbing pipe, (1.25" and 1.5") which was a mistake."

Most large exhaust and muffler shops make exhausts out of SS .

It is not expensive so going up to 2 or 2 1/2 with a SS muffler wont be a boat style outlay.

Plan B could simply be replacing the galvanized pipe with black , easily found at a real plumbing supply house.
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Old 05-20-2019, 08:49 AM   #6
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What Lepke said. I've had zinc poisoning. I was so sick it was painful. There is no cure other than time. Get rid of the zinc piping.
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Old 05-20-2019, 11:41 AM   #7
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I have ordered new stainless fittings to replace all galvanized. Sometimes I wish I could drive to a store.
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