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Old 10-29-2015, 05:13 PM   #1
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The exhaust mixers (pic 1) on my Yanmar 4LH-DTE's left much to be desired. The seawater injection point was very close to the turbo and (in my case) external water level was/is, within 5" of turbo level.

Some online homework, including Boatdiesel, left me in no doubt that the hot part of an exhaust tract should go up and over before sea-water is injected - unlike the Yanmar elbow. Funds were limited, so pics 2, 3 and 4 are what I came up with. The water injection port is partially hidden by the down pipe in the seconds pic.

I seem to have got the mixer right because I can confortably put my hand on the exposed bit (just above the blue hump-hose) when the engines are pushing.

The hot risers got two layers of header-wrap as overhead clearance is minimal. It's applied wet and the blue dye-stuff gets everywhere! Can you spell wode!

The welded components are Sch #10 stainless pipe, elbows, end caps and flanges ordered from McMaster-Carr. The majority is 3" and the cost for both engines was around $350.00, TIG welding around the same again and the Trident elbows etc around $500.00.

I am a worrier, so water-flow and exhaust temperature alarms are on order from Aqualarm.
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Old 10-29-2015, 05:17 PM   #2
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Greetings,
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Old 10-29-2015, 05:19 PM   #3
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Looks mostly good. One issue you may have is there is nothing to try to spread the injected water around the diameter of the injection ring. May ge a hot spot in the hose opposite the water nozzle. Sometimes there is plenty of turbulence to mix hot gas and water, sometimes not.

Check for hotspots at various rpms.
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Old 10-29-2015, 07:42 PM   #4
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nice work. How did you connect the raw water to the mixer?
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Old 10-29-2015, 08:43 PM   #5
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Other than the geometry problem, did you have any sea water corrosion in your turbo that caused you to do this?

Your new riser/mixer certainly is an improvement, but I note that the outlet from the lift muffler looks like it is higher than the new riser elbow. That could potentially allow the muffler to fill with sea water after numerous, long term stern waves hitting, and then get high enough to go over the new riser.

I know it is counter intuitive, but it looks like it would be easy to cut off several inches from the outlet pipe so it doesn't go up as high. That will let any water that builds up in the muffler to flow back out before it gets into the riser.

Look at the attached pic of Tony Athens inherently safe exhaust system for more specifics.

I also support Ski's suggestion to put more spacers where the water flows out into the exhaust stream. You need enough pressure drop across those spacers to distribute the flow around the periphery even at idle.

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Old 10-29-2015, 09:20 PM   #6
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It looks really good but I would be concerned that there is too much torque on that turbo - the entire weight of that exhaust is unsupported except by that turbo flange. I would add a support that goes from the engine somewhere, perhaps the mount, to the exhaust pipe. The support pipe must be attached to the engine or it will not allow the engine and the exhaust to move independently when vibrating or torquing and mounting it to the boat would make more vibration and noise.
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Old 10-29-2015, 11:36 PM   #7
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Nice improvement! Let us know how your improvement does in the long run!
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Old 11-01-2015, 10:41 AM   #8
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Thanks to all for the input.

Barnacle: The water injection port is hidden behind the down pipe in the second pic. See the pink arrow.

Ski and David: I was/am concerned about the even spread of water in the jacket and quite expected a dry/hot spot on the side opposite to the water inlet. However, so far so good. I can confortably put my hand on the exposed stainless bit just above the blue hump-hose with the engines at idle and at low throttle settings. Thus the jacket seems to be running full. I am concerned about how well exhaust and sea water mix at higher revs. I don't want un-cooled exhaust gas hitting the blue elbow. I will be doing some hand-on-elbow tests while someone else drives the boat. I have some grounds for hope as the new mixer and the old Yanmar one have much the same dimensions and lack of restriction. Also the water inlet hose and the jacket have much the same cross-section, so if one runs full the other should too (nice theory eh?).

David: Yes, both turbos had some corrosion on the dirty side. I don't understand exactly why, as they are some 5" above the water-line and I have never been in a situation where water was being driven back into the transom. Perhaps because the Yanmar mixers allowed seawater so close to the turbo outlets - I don't know. Fortunately I caught it in time. Whatever the cause, I feel comfortable I can prevent its recurrence with the new arrangement.

I will give serious consideration to shortening the muffler outlet hose. Meanwhile I take some comfort from the fact that water being pushed into the transom ports has to rise some 12" before it can flow into the muffler.

Xs: Likewise I will give further thought to supporting the turbo - I had considered this when putting it all together. The hump-hose is where it is to isolate the turbo from the rest of the exhaust system.
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Old 11-01-2015, 11:02 AM   #9
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David: Yes, both turbos had some corrosion on the dirty side. I don't understand exactly why, as they are some 5" above the water-line and I have never been in a situation where water was being driven back into the transom. Perhaps because the Yanmar mixers allowed seawater so close to the turbo outlets - I don't know.
It's more than likely because the exhaust is open to moist salt air coming back up to the engine while at rest.

You can see the results sometimes in the combustion chambers of the cylinders that end up with there exhaust valves open at rest.

That is why engine block heater can be a good thing even in the summer.
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Old 11-01-2015, 11:19 AM   #10
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Nice work and definite an improvement in where the water enters but I agree there is a lot of vibrating mass attached to that turbo. Perhaps a support from the engine, not the boat, is in order.
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Old 11-01-2015, 11:26 AM   #11
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Maybe I am just dense.
I don't see why you would go to all of that trouble and expense. Your Yanmar exhaust elbow is tried and true, and is similar to most other brands in that the water injection occurs just above the fibre pipe connection at the bottom of the casting. That design has been around long enough that any manufacturer finding it to be inadequate has long ago made the necessary modifications. With the exhaust gases being expelled from the engine under pressure, there is no fear of a back flow of injected water, so the only thing you need to be concerned about is water coming up the pipe from the transom while the engines are not running. With the large sized water lift mufflers in your pix, that scenario is remote and other, less costly forms of insurance are available, such as a flap on the outlet or a rise in the pipe as it exits the muffler.
With your modification, you have added a lot of weight to the attachment at the turbo, so will need to monitor the first section of pipe for stress at that connection, and also the turbo casting itself, to be sure that it can handle the extra weight.
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Old 11-01-2015, 12:55 PM   #12
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one reason is that at shutdown engines sometimes turn backward a bit sucking air in from the exhaust. The further the better.
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Old 11-01-2015, 01:03 PM   #13
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Maybe I am just dense.
I don't see why you would go to all of that trouble and expense. Your Yanmar exhaust elbow is tried and true, and is similar to most other brands in that the water injection occurs just above the fibre pipe connection at the bottom of the casting. That design has been around long enough that any manufacturer finding it to be inadequate has long ago made the necessary modifications. With the exhaust gases being expelled from the engine under pressure, there is no fear of a back flow of injected water, so the only thing you need to be concerned about is water coming up the pipe from the transom while the engines are not running. With the large sized water lift mufflers in your pix, that scenario is remote and other, less costly forms of insurance are available, such as a flap on the outlet or a rise in the pipe as it exits the muffler.
With your modification, you have added a lot of weight to the attachment at the turbo, so will need to monitor the first section of pipe for stress at that connection, and also the turbo casting itself, to be sure that it can handle the extra weight.
Don't be so sure. 5 inches above the waterline is downright frightening. So he had reason for concern. And the corrosion on the dirty side of the turbos pretty much proves that....not just moisture but water intrusion. Like the sketch above, 12 inches should be considered minimum. The actual elbow may be "tried and true" but its installation varies from boat to boat. In this case, it did not adhere to what is conisdered the minimum above the waterline. You can get into a case where the boat is docked or at anchor with a beam sea. All you need is a 5 inch ripple and you are risking water ingress. And in case you didn't know, water is pretty damned determined to get where it can. So rocking back and forth for an extended time could easily push water back through the turbo.
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Old 11-01-2015, 03:03 PM   #14
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That design has been around long enough that any manufacturer finding it to be inadequate has long ago made the necessary modifications.
Manifestly, definitely, absolutely not so. Look at Mainship Pilot 34s, Legacy 28s, most maybe all Carolina Classics, the list goes on on and on where manufacturer's have not "made the necessary modifications".

Follow boatdiesel for a month. There are at least three active threads at any one time about these situations. It is the most active topic on that forum.

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Old 11-04-2015, 11:07 AM   #15
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Great improvement! I'm curious as to where you purchased the reducer from the 4" to 3" tube. I couldn't find it on the Mcmaster website.
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Old 11-04-2015, 01:58 PM   #16
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Gordy: The pipe sizes are 3-1/2"and 3". The item you are looking at is not a reducer, its a 3-1/2" end cap with a hole cut in it to accept a short length of 3" pipe.
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Old 11-04-2015, 03:32 PM   #17
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Brilliant!
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Old 11-04-2015, 04:26 PM   #18
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Gordy: The pipe sizes are 3-1/2"and 3". The item you are looking at is not a reducer, its a 3-1/2" end cap with a hole cut in it to accept a short length of 3" pipe.
How did you cut that big hole in 316 stainless? Do you have a plasma rig?

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Old 11-04-2015, 05:22 PM   #19
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I used a small vertical mill with the end cap in a 3-jaw vice mouted on a rotary table. It would have been possible to use a hole-saw but I can't bring myself to be that unkind to innocent tools.

A plasma cutter would be nice - Christmas is not too far off.
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Old 11-06-2015, 10:12 PM   #20
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Nice job. I did a similar but simpler version with my Perkins. Purchased the SS elbows and piping online and TIG welded it up. Total cost was around $150, including the argon. If I bought the OEM for the 1977 Perkins it would have been at least $2k. I mostly followed the original pattern but have thicker stainless steel and also added a pyrometer fitting.
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