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Old 23-11-2017, 22:22   #16
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Re: Exhaust Plumbing Bypass Stern Squirt

You can chip alot of the corrosion out and keep it as a spare. Not only do they clog up but they can crack as well. I saw a cat stuck in a remote place due to this.
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Old 24-11-2017, 02:15   #17
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Re: Exhaust Plumbing Bypass Stern Squirt

Since I am currently working on my inboard engine installation, Which is something I have not done before, I spent a day on line reading up on the subject. One link that I came across explained that, Often the desired Volume of sea water passing through the heat ex-changer to cool the engine can exceed the amount of water actually needed to be sprayed into the mixing elbow to cool the exhaust. Thus a bypass between the heat ex-changer and the mixing elbow is used to jettison a portion of the water because without this: The excess water can cause an undesirable back pressure.

It was explained that this solution is especially useful in tropical climates where the sea water is consistently warmer. or more so with large engine installations,

I do not think I need to include it in a 28 HP installation. I also hope that Volvo engineers have sized the raw water pump to draw and send the correct amount of water into the system at all engine speeds?
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Old 24-11-2017, 10:09   #18
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Re: Exhaust Plumbing Bypass Stern Squirt

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Originally Posted by daletournier View Post
I don't understand this? How does water exiting through the exhaust create back pressure? replacing space that could be used for exhaust gas? Sorry, don't get it, no criticism.


Salt water weighs about 9 lbs per gallon I think. It takes energy of course to lift all that weight into the air and blow it out of the exhaust.
Of course this energy comes from the exhaust and causes back pressure. Less water, less back pressure.
I understand the concept, just never thought about it before.
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Old 24-11-2017, 15:56   #19
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Re: Exhaust Plumbing Bypass Stern Squirt

a64pilot....looking for clarification of you last line,.. I understand the concept, just never thought about it before.

Does this mean that you think the the concept of a bypass has some usefulness or merit?
With the plastic boxes of water lock, Goose neck, and Silencer installed in the exhaust line.(Manufactured by Vetus of Holland) My concern with using the technique; Is how to know how much the sea water flow though the mixing elbow can be reduced with out melting and compromising them.

we all realize that; of course Water depending on temperature: can be in the states between solid ice and gaseous steam. So being 'NEW" to considering this wet exhaust system I have been trying to find an explanation concerning the content of a normal wet exhaust. As to what percentage is water, As opposed to what percentage is steam or water vapour.

Obviously the greater proportion of steam or water vapour would cause much less back pressure drag on the engine. I note that Vetus require a down slope from the top of the goose neck to the transom exhaust fitting.

This caused me to wonder IF...At the point of mixing the cooling water is virtually completely vaporized, thus assisting its passage down through the Water lock and up through the height of the Goose neck. So that the content exiting the transom exhaust fitting as spurts of water is in fact condensate that reverted to the liquid state by cooling on its transition though the Silencer Box and rubber exhaust pipe.Thus being blown out by the diesel exhaust Gas???

Does anyone else have a clearer analysis of the process?

Sincerely Brian. AKA Coastalexplorer.
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Old 24-11-2017, 16:25   #20
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Re: Exhaust Plumbing Bypass Stern Squirt

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Originally Posted by a64pilot View Post
Salt water weighs about 9 lbs per gallon I think. It takes energy of course to lift all that weight into the air and blow it out of the exhaust.
Of course this energy comes from the exhaust and causes back pressure. Less water, less back pressure.
I understand the concept, just never thought about it before.
The other reason is to alleviate the back pressure caused by smallish wet exhaust diameters. There's is almost always more raw cooling water than required entering the mixing elbow to cool the dry exhaust to satisfactory temps. Anymore than what is required just takes up space in the wet exhaust and reduces the amount of available volume for the exhaust gases.
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Old 24-11-2017, 16:35   #21
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Re: Exhaust Plumbing Bypass Stern Squirt

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Originally Posted by coastalexplorer View Post
a64pilot....looking for clarification of you last line,.. I understand the concept, just never thought about it before.

Does this mean that you think the the concept of a bypass has some usefulness or merit?
With the plastic boxes of water lock, Goose neck, and Silencer installed in the exhaust line.(Manufactured by Vetus of Holland) My concern with using the technique; Is how to know how much the sea water flow though the mixing elbow can be reduced with out melting and compromising them.

we all realize that; of course Water depending on temperature: can be in the states between solid ice and gaseous steam. So being 'NEW" to considering this wet exhaust system I have been trying to find an explanation concerning the content of a normal wet exhaust. As to what percentage is water, As opposed to what percentage is steam or water vapour.

Obviously the greater proportion of steam or water vapour would cause much less back pressure drag on the engine. I note that Vetus require a down slope from the top of the goose neck to the transom exhaust fitting.

This caused me to wonder IF...At the point of mixing the cooling water is virtually completely vaporized, thus assisting its passage down through the Water lock and up through the height of the Goose neck. So that the content exiting the transom exhaust fitting as spurts of water is in fact condensate that reverted to the liquid state by cooling on its transition though the Silencer Box and rubber exhaust pipe.Thus being blown out by the diesel exhaust Gas???

Does anyone else have a clearer analysis of the process?

Sincerely Brian. AKA Coastalexplorer.
Brian,

When you're using Vetus plastic waterlifts and goosenecks you should not be making very visible steam. The maximum continuous temperature is 158° F. Steam is 212°, you need more water to reduce temps.
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Old 24-11-2017, 17:37   #22
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Re: Exhaust Plumbing Bypass Stern Squirt

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This is the good way to do it. No spring, no plastic piston to seize. When needed, flush with fresh.

Or think differently and dispose of the anti-siphon completely.
http://www.cruisersforum.com/attachm...xhaust-med.jpg
That system ONLY works if you can maintain the injection port a minimum of 11" above the load waterline as shown in the drawing. If you tried it with a typical sailboat installation where the injection elbow can be below the water line you'll be in a world of hurt...

Of course if you were almost a foot above the waterline at the injection port, an antisyphon isn't as critical--even in a conventional installation...
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Old 24-11-2017, 18:34   #23
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Exhaust Plumbing Bypass Stern Squirt

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Brian,

When you're using Vetus plastic waterlifts and goosenecks you should not be making very visible steam. The maximum continuous temperature is 158° F. Steam is 212°, you need more water to reduce temps.


Steam is at least 212F, likely much higher, plus the energy in steam is much higher as it is water that has gone through a phase change.
Steam at 212F will burn you much more severely than water at 212F.

However I believe that water separators work by separating the water from the exhaust well down stream from the point of injection, after it has dropped the temp of the exhaust gases, so pulling the water from the system prior to it being injected into the exhaust is risky, I can see it being fine, then later your strainer gets a little clogged or you impeller worn or whatever reduces the water flow, then you could burn up your exhaust components.
However a little pee like what comes out of an outboard surely isn’t enough to be a concern?
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Old 24-11-2017, 19:30   #24
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Re: Exhaust Plumbing Bypass Stern Squirt

Isn't the above just a case of a poorly designed exhaust system? Using the anti siphon loop is a band-aid. I've never seen this.
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Old 25-11-2017, 08:24   #25
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Re: Exhaust Plumbing Bypass Stern Squirt

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UPDATE: After replacing the mixing elbow the vale/siphon no longer squirts water at idle, and doesn’t shoot as far at higher rpms. My guess is that the elbow was so clogged that it was backing up and out the siphon. Now I wish I had a video for comparison and illustration/reference purposes.

I would post a pic of the old elbow but it looks just like all the other corroded ones on the web
That's the same assumption I would make.

One other thought, just make sure that "squirt" line has no dips or other water traps. If it does and your engine is at or below the water level, you could have back siphoning through the raw water lines and get salt water into your engine.

Best practice for that line is to have it sloping downward for it's entire length if its long or upwards it's entire length if it's short. But no up and downs in the run to form a water trap.
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Old 25-11-2017, 08:30   #26
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Re: Exhaust Plumbing Bypass Stern Squirt

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Isn't the above just a case of a poorly designed exhaust system? Using the anti siphon loop is a band-aid. I've never seen this.
Not if the engine is installed at or below the working water level, it's an essential part of the system. In fact the "pee" line is actually the best type of anti siphon for wet exhaust.

Done correctly, it can serve 3 purposes: anti siphon, positive indication of raw water flow and trimmer for exhaust temp vs. back pressure reduction.
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Old 25-11-2017, 08:43   #27
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Re: Exhaust Plumbing Bypass Stern Squirt

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Isn't the above just a case of a poorly designed exhaust system? Using the anti siphon loop is a band-aid. I've never seen this.
My memory isn't as good as it used to be, but I seem to remember the exhaust anti siphon on the Catalina 470 is directly above the aft end of the engine by the primary fuel filter. Catalina uses a spring loaded plastic check valve. they can fail if encrusted with salt or leak if not maintained.
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Old 25-11-2017, 09:11   #28
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Re: Exhaust Plumbing Bypass Stern Squirt

Yes the 470 has it around that area, boat to boat they can differ in location and (not sure why) , yes I agree they can and do salt up I've experienced this on a previous boat. I understand getting rid of the valve is a good solution if you can route the hose appropriately , ive said that in a previous post early on in the thread.
What I'm not convinced of is the need to add the hose to relieve back pressure? I understand the reasoning, but a exhaust system designed to match the engine etc shouldn't suffer from a back pressure problem? Hose diameter and height being the determining factors.
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Old 25-11-2017, 09:41   #29
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Re: Exhaust Plumbing Bypass Stern Squirt

Threads like this are good, they bring things such as anti siphon valves to the forefront of my mind.

As mentioned in previous post, I've had a antisiphon valve salt up and hydrolock my engine on a previous boat, twice(I love decompression valves) this was due to it not being as high as I would like ( should of been) and not having the room to go higher, it was always a concern. I pulled the cap off (nanni) this particular valve and got into the habit of reaching under the sink and manually depressing the valve directly after engine shut down.

On my current boat the antsiphon valve is in a stupid spot that's not easy to access.

Now what's to stop me adding a hose to it like we are talking about, but with a antsiphon valve in the end and running it to a convenient spot that allows me to access it easily?

I can't run a hose with out a valve that drips overboard, and it's a hassle to reroute the current hoses and valve setup to a different location, but would be easy to run a hose of the end and direct that to a better spot.
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Old 25-11-2017, 09:53   #30
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Re: Exhaust Plumbing Bypass Stern Squirt

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Yes the 470 has it around that area, boat to boat they can differ in location and (not sure why) , yes I agree they can and do salt up I've experienced this on a previous boat. I understand getting rid of the valve is a good solution if you can route the hose appropriately , ive said that in a previous post early on in the thread.
What I'm not convinced of is the need to add the hose to relieve back pressure? I understand the reasoning, but a exhaust system designed to match the engine etc shouldn't suffer from a back pressure problem? Hose diameter and height being the determining factors.
Dale,

What you said about not being needed to reduce back pressure is only true if the boat builder follows the recommendations of the engine manufacturer. Sadly, many don't for various reasons; cost, interior design and space limitations to run the hose. Catalina sadly is not immune to these short cuts. On the 4JH series from the late 90's onward, Yanmar specified a 3" wet exhaust. Catalina has fitted a 2" wet exhaust and mixing elbow from an earlier series 3 cylinder engine. All done under the very watchful eye (wink wink) of Mastry. Those engines, especially the high revving ones fail the back pressure test. I know, I've done the tests.

Sometimes, fitting an overflow line of sufficient size in lieu of the anti siphon will reduce the volume of cooling water enough to reduce the back pressure readings to acceptable levels and still keep the exhaust temps low enough.

Hopefully your turbo charged Yanmar was fitted out with the bronze box mixing elbow and 3" wet exhaust throughout.
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