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Old 11-12-2013, 18:30   #1
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Water lift muffler and rerouting exhaust hose

In my boat the water lift muffler is flush against the aft bulkhead of the engine room. So the only way for the exhaust to route to the stern is up and forward across the engine room, loop down and back aft. The makes the hose quite long and it makes access to one side of the engine more difficult.

I would like to reroute the exhaust hose but due to the location of the muffler the only option is to use some sort of elbow since the hose cannot make the sharp bend to go directly aft.

So, the question, is there any potential down side to putting an elbow or two in the exhaust hose between the water lift muffler and the exit at the transom? If I do this, any installation issues to be aware of?

Thanks
Skip
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Old 12-12-2013, 01:31   #2
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Re: Water lift muffler and rerouting exhaust hose

none that I could think of except heat, but I would be interested in seeing what answers you get as I was also thinking of adding a right hand bend just before the stern.
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Old 12-12-2013, 04:52   #3
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Re: Water lift muffler and rerouting exhaust hose

When you run a dryer vent or a kitchen vent in a house, a 90 degree bend is equal to five feet of duct. Following that logic, the elbow in the exhaust system may make it too long a run, and create back pressure, which, besides cutting engine performance, could also allow cooling water to stay in the system, and possibly back up into the engine.
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Old 12-12-2013, 05:26   #4
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I have two centek fiberglass elbows that I installed for the same reason you did. I have not been able to perceive any problems with back pressure or holding water.
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Old 12-12-2013, 05:37   #5
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Re: Water lift muffler and rerouting exhaust hose

Replaced my entire exhaust system going from 2" to 3" this created a need for a 90 degree elbow connecting the stand pipe to the muffler. When finished I ran the boat WOT for a mile no issues a year later all is well.
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Old 12-12-2013, 07:45   #6
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Re: Water lift muffler and rerouting exhaust hose

Quote:
Originally Posted by keepondancin View Post
When you run a dryer vent or a kitchen vent in a house, a 90 degree bend is equal to five feet of duct. Following that logic, the elbow in the exhaust system may make it too long a run, and create back pressure, which, besides cutting engine performance, could also allow cooling water to stay in the system, and possibly back up into the engine.
Thanks KoD. Good points. Regarding the back pressure from adding a 90 degree elbow, would that not depend a great degree to the radius of the bend? So a large 90 might add only minimal additional back pressure where a tight radius 90 a lot.

Also in my case I will be able to shorten the overall length by about 15' by adding the elbows so think I should see a net reduction even with the bends added.
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Old 12-12-2013, 08:48   #7
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Re: Water lift muffler and rerouting exhaust hose

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Originally Posted by Sailmonkey View Post
I have two centek fiberglass elbows that I installed for the same reason you did. I have not been able to perceive any problems with back pressure or holding water.
Thanks Sailmonkey. Encouraging news and also answered my next question, what material should I use for the elbows. Am checking out the Centik options.
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Old 12-12-2013, 08:51   #8
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Re: Water lift muffler and rerouting exhaust hose

Quote:
Originally Posted by casual View Post
Replaced my entire exhaust system going from 2" to 3" this created a need for a 90 degree elbow connecting the stand pipe to the muffler. When finished I ran the boat WOT for a mile no issues a year later all is well.
Thanks. Long term experience is reassuring. Unfortunately I am already at 3", which is part of the problem, so don't want to go any larger. But from all information so far I think I'm good.
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Old 12-12-2013, 09:19   #9
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Re: Water lift muffler and rerouting exhaust hose

Many engine manufacturers specify the maximum back pressure that is acceptable. Friends who repowered with a Cummins had to make expensive mods to the exhaust in order to comply with such specs... the warranty was void otherwise, and the factory rep came out to the boat and measured the pressure in situ.

So, if you care to investigate, it is likely that real info is available for basing your decision.

Cheers,

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Old 12-12-2013, 09:20   #10
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Re: Water lift muffler and rerouting exhaust hose

If you post a pic or two someone might have a different idea about how to route it.

I replaced my exhaust system last year. There were quite a few bends in the main length. I decided to go with a more flexible hose and do it in a single piece instead of using elbows. I used Vetus 3" corrugated hose and it was easily able to make all the bends. I did have to change some of the thru bulkhead holes into ovals in order to eliminate the elbows.

The flexible hose was expensive, but so are the elbows and good "t" bolt hose clamps (double clamped).

Cheers,
JM.
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Old 12-12-2013, 09:24   #11
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Re: Water lift muffler and rerouting exhaust hose

Shields and Trident both make black rubber and blue silicone elbows that can connect directly to the muffler or exhaust port. Trident (at least) also makes tube connectors for connecting the elbows to hose. I find that the Shields elbows turn a tighter radius than Tridents for the same diameter.
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Old 12-12-2013, 10:35   #12
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Re: Water lift muffler and rerouting exhaust hose

Quote:
Originally Posted by Jim Cate View Post
Many engine manufacturers specify the maximum back pressure that is acceptable. Friends who repowered with a Cummins had to make expensive mods to the exhaust in order to comply with such specs... the warranty was void otherwise, and the factory rep came out to the boat and measured the pressure in situ.

So, if you care to investigate, it is likely that real info is available for basing your decision.

Cheers,

Jim
What a concept. Do some real calculations based on real world data.

Well don't have the engine specs at hand but did some calculations to compare relative back pressure of a longer hose without elbows to a shorter hose with elbows and the difference appears to be minimal. Did not yet find data to account for a large diameter hose loop of 270 degrees so I ignored that which should make the numbers compare even better.
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Old 12-12-2013, 10:38   #13
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Re: Water lift muffler and rerouting exhaust hose

Quote:
Originally Posted by NahanniV View Post
If you post a pic or two someone might have a different idea about how to route it.

I replaced my exhaust system last year. There were quite a few bends in the main length. I decided to go with a more flexible hose and do it in a single piece instead of using elbows. I used Vetus 3" corrugated hose and it was easily able to make all the bends. I did have to change some of the thru bulkhead holes into ovals in order to eliminate the elbows.

The flexible hose was expensive, but so are the elbows and good "t" bolt hose clamps (double clamped).

Cheers,
JM.
Due to the cramped engine space, multiple angles and small access areas I'm looking at for rerouting the hose I think photos might not help. BUT, was not aware of the availability of flexible, corrugated hose. That might simply the changeover dramatically. Thanks
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Old 12-12-2013, 10:40   #14
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Re: Water lift muffler and rerouting exhaust hose

Quote:
Originally Posted by JayH View Post
Shields and Trident both make black rubber and blue silicone elbows that can connect directly to the muffler or exhaust port. Trident (at least) also makes tube connectors for connecting the elbows to hose. I find that the Shields elbows turn a tighter radius than Tridents for the same diameter.
Thanks. I've been using Trident hose in several places on the boat and they seem to be top of the line.
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Old 12-12-2013, 10:42   #15
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Re: Water lift muffler and rerouting exhaust hose

The elbow also restricts the inside diameter quite a bit if it is fiberglass. 3" elbow, 1/4" glass (?) = 2.5 inside diameter etc.
However your long loop is not so good either... Maybe you could glass an elbow right onto your muffler...?
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