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Old 07-05-2014, 03:38   #16
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Re: Fiberglass exhaust elbows

Would silicon tubing give you the flex you want?? I have been thinking of using it instead of heavy rubber for some time. It will cost more but the less stress on bits may balance that out.
I have been looking at the cracks that appear in the 1GM mixing elbow & think there is a conection to the stress cracks in the stainless because of the vibration & heavy rubber tubing.
Regards Bill
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Old 07-05-2014, 09:48   #17
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Re: Fiberglass exhaust elbows

Yeah, that hose is stiff for sure. On my 3" exhaust I added a SS bellows, and many power boats have them.
OP: if your hose slopes toward the engine from the stern with no muffler you really should try to put a loop above the exit somehow.
On one boat, I even had a large muffler, the exhaust exit was about 2-3 " above the water line. Once sitting at the dock the water was lapping into the exit fitting (wind from the stern). It gradually filled the whole system. When I started the engine next am I bent a pushrod and had a fouled injector. I must have just started it in time before I would have been water locked!
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Old 07-05-2014, 11:10   #18
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Re: Fiberglass exhaust elbows

Quote:
Originally Posted by Cheechako View Post
Yeah, that hose is stiff for sure. On my 3" exhaust I added a SS bellows, and many power boats have them.
OP: if your hose slopes toward the engine from the stern with no muffler you really should try to put a loop above the exit somehow.
On one boat, I even had a large muffler, the exhaust exit was about 2-3 " above the water line. Once sitting at the dock the water was lapping into the exit fitting (wind from the stern). It gradually filled the whole system. When I started the engine next am I bent a pushrod and had a fouled injector. I must have just started it in time before I would have been water locked!
The exhaust exit sits about 15" above the water and there is a high loop in the engine room but that is far from the exhaust exit. I will take comfort in the fact that the boat has operated this way without issue for 32 years.

As you can figure from these picture, unless I brought that exhaust loop up between my pillows it just is not going to happen.

On the other topic of the dis-similar metals I found that "Red Brass" is used as a substitute for non-existent bronze nipples (at least in the size that I need).
Confirmed by one of our own commercial members here:
Bronze vs Red Brass fittings
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Old 07-05-2014, 11:23   #19
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Re: Fiberglass exhaust elbows

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Originally Posted by bill good View Post
Would silicon tubing give you the flex you want?? I have been thinking of using it instead of heavy rubber for some time. It will cost more but the less stress on bits may balance that out.
I don't think even the silicone hose would flex as much as I need without kinking. I would need a 180 degree loop down into the bilge within about 24" wide to avoid using the fiberglass elbows. It might allow me to use only one though.

I have seen preformed bends in silicone for automotive applications but I have not looked for the wire reinforced hose I would need in this application. Might be worth a search though, I like the silicone hose and I hear it seals much better at the fittings.
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Old 07-05-2014, 11:30   #20
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Re: Fiberglass Exhaust Elbows

On my generator I use a 2" corrugated silicone hose. It's only disadvantage is it's price tag.
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Old 07-05-2014, 11:38   #21
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Re: Fiberglass exhaust elbows

I have seen preformed bends in silicone for automotive applications but I have not looked for the wire reinforced hose I would need in this application. Might be worth a search though, I like the silicone hose and I hear it seals much better at the fittings.[/QUOTE]

For what it's worth, There are elbows used in/on aircraft that use a fiberglass elbow with short bits of silicone hose bonded to the ends. There is no wire needed. They would be way to expensive for a boat but it might be an inspiration..
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Old 07-05-2014, 12:17   #22
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Re: Fiberglass Exhaust Elbows

"The exhaust exit sits about 15" above the water and there is a high loop in the engine room but that is far from the exhaust exit. I will take comfort in the fact that the boat has operated this way without issue for 32 years."
That sounds like a pretty good setup.
BTW the boat I had the problem on was a 1982! One time, the right wind and water....
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Old 08-05-2014, 18:00   #23
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Re: Fiberglass Exhaust Elbows

Instead of worrying about the water that might come in by way of the through hull, I'd be more concerned by the water coming through your raw water pump siphoning back into the engine on shutdown.

There's a wealth of information concerning wet exhaust systems on the boatdiesel.com website, and more specifically in an article by Tony Athens that I think everybody should read before doing something that might cost them an engine or two.

Jacques
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