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Old 19-08-2015, 10:45   #1
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Interesting Exhaust Loop Setup Needs Fixing

I have a fairly bizarre loop setup on my exhaust, and am currently having trouble with it. Any help on understanding it from you fine folks would be appreciated.

There is a custom made u-shaped loop on the exhaust side of my engine's cooling water. It has 3 lines (formerly 4) going into it, and lacks an anti-siphon valve or air hole entirely.
- Going into the center of the arch of the U is the 1" coolant line coming out of the raw water intercooler
- The left side of the U is a 3/4" line leading to the exhaust elbow water injection
- The right side is a 1" line leading to the top of the gooseneck at the stern
-There used to be a 3/4" line welded into the left (exhaust elbow line) that led to a port on the intake of the waterlock muffler. I replaced the muffler, and saw no need to add this extra plumbing back in to the new one

The loop is led to about 10" above the waterline on the centerline of the boat. The engine is totally below the waterline.

Due to an older impeller, water can freeflow through the raw water intake, past the impeller, into this high loop, and then to the exhaust elbow, where it fills the muffler and eventually the elbow, cylinders, and then flows out of the air intake. Replacing the impeller seems to be a short term fix. Currently, we turn the raw water intake off and on for engine operation, but this also could lead to disaster if forgotten.

Any idea what was going on in the designer's mind? If I replace with an anti siphon loop from the engine to the exhaust elbow, thus removing the 1" line to the gooseneck, will I cause new problems?

Help! We just rebuilt this engine and already hydrolocked it once. No damage, but this setup makes me nervous.

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Old 19-08-2015, 11:14   #2
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Re: Interesting Exhaust Loop Setup Needs Fixing

Why not just remove the whole mess and put in a normal riser with mixing elbow and an anti siphon well above the heeled waterline?
I've never heard of a mess like what you're describing!


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Old 19-08-2015, 11:20   #3
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Re: Interesting Exhaust Loop Setup Needs Fixing

I very well may do just that. I'm thinking that this is mostly original (the gooseneck is a stainless steel custom job, as was the old waterlock muffler, typical of production parts on this boat), and that the long run of the exhaust hoses from the engine amidships to the stern outlet gave reason for the hose to the gooseneck. The reason why it was this way is what I want to understand beforehand, rather than after I have changed it all around.
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Old 19-08-2015, 14:22   #4
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Re: Interesting Exhaust Loop Setup Needs Fixing

Run the 1 inch hose from the intercooler into the 1 inch inlet on the right side of the U. Leave the 3/4 line on the left side of the U alone, going to the elbow.

Take the center 1 inch hose and step it down to about 1/2 inch hose and run that 1/2 inch hose to the top of the goose neck aft. Make sure this hose runs up, then aft, then down to the goose neck. No dips or hollows in this hose. This hose will become the air line to make the siphon break work.

Now, lift the entire assembly up at least 5 or 6 inches, if not more. 10 inches above centerline is not enough to guarantee no problems when the boat is heeling.

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Old 20-08-2015, 10:20   #5
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Re: Interesting Exhaust Loop Setup Needs Fixing

Interesting DougR. I thought the same thing, except for your comment about not allowing the hose to the gooseneck to drop until it reached the gooseneck. Right now, it does in fact run straight down the same path as the exhaust hose, rising up to meet the gooseneck.

I will definitely raise the loop as high as possible, around 12" above waterline unless I go through some acrobatics to run the loop somewhere else.

If I eliminated this hose altogether, plugged the port on the gooseneck, and had a regular groco anti siphon loop on the engine, do you think I would be cutting out something important?

I guess this is one more argument to keep the boat light and not loaded down with all of our liveaboard junk!
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Old 20-08-2015, 11:27   #6
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Re: Interesting Exhaust Loop Setup Needs Fixing

Changing the location of the plumbing to somewhere else "on the engine" won't make any difference because your system is essentially " on the engine" now.
What you can do however is to remove the hose running from the inverted U to the stern gooseneck and place a normal anti siphon valve where the hose used to connect to the U. Block off the hole at the gooseneck. Then elevate the entire stainless assembly as high as you can.

One thing I didn't comment on yesterday.... The reason that there was a hose bypassing the elbow and going directly into the muffler was an attempt to lower exhaust back pressure. When water is injected into the elbow and hits the 900 degree exhaust gas, the water flashes into steam, and this steam volume causes high back pressure. Bypassing some of the cooling water around the exhaust elbow cuts down on the steam volume and lowers back pressure. If your system is long and convoluted it might have been necessary to get within the engine manufacturers back pressure limits. It wouldn't hurt to do a backpressure test to be sure things are within limits.

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Old 20-08-2015, 14:24   #7
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Re: Interesting Exhaust Loop Setup Needs Fixing

If the engine hydro locked don't forget to change the oil.
I would toss the U thing out and buy a Vetus or similar antisyphon. Install as instructions. On the fore / aft centreline as high as possible so it is above the heeled waterline on either tack. Bleed line should run with no dips same height and out the centre of the transom. No valve to stick in my Vetus. Some water dribbles out the transom line but air can enter to prevent syphon. Cooling water from engine in one side of Vetus inverted U and out into exhaust from other side.
A large waterlock at least 1' / 300mm below the exhaust bend in the lowest point of the flexible exhaust piping is essential to collect exhaust water when the motor is shut down. A waterlock acts as a muffler which should not be needed additionally
Check any waterlock has no restriction. Some have various tails to cut off. Google marine waterlock if you don't know what I mean. Also Google Vetus antisyphon.
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Old 20-08-2015, 15:20   #8
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Re: Interesting Exhaust Loop Setup Needs Fixing

Some people run a 1/4" tube up and out to the cockpit. They then angle it down so the water is aimed at a cockpit drain. This is safer than an anti siphon valve and also lets you know the pump is working.
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Old 20-08-2015, 15:55   #9
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Re: Interesting Exhaust Loop Setup Needs Fixing

Quote:
Originally Posted by DeepFrz View Post
Some people run a 1/4" tube up and out to the cockpit. They then angle it down so the water is aimed at a cockpit drain. This is safer than an anti siphon valve and also lets you know the pump is working.
Yes that's a good idea. Each boat is different. I have a tiller hole for a drain at cockpit floor level and a slightly raised ocker under the tiller so I split the syphon bleed line either side of the locker so it works on either tack.
I think the anti syphon units with a bleed line are more reliable than with a valve
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Old 20-08-2015, 16:12   #10
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Re: Interesting Exhaust Loop Setup Needs Fixing

Quote:
Originally Posted by DeepFrz View Post
Some people run a 1/4" tube up and out to the cockpit. They then angle it down so the water is aimed at a cockpit drain. This is safer than an anti siphon valve and also lets you know the pump is working.
We have something like that. I plumbed it out the side of the boat instead of into the cockpit. It's still easy to check on our boat. Super happy with it.
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