Sheerwood GC1 or GC5 fits 6 BT?

[Kjell Lindroos]

I have a boat with a Cummins 6 BT (1997 model) with 5600 h on it. The marine gear is a ZF63A.
I bought the boat a year ago.
During 2021 I have renewed raw water intake with valve, all hoses, raw water pump (original Sherwood M71), marine gear oil cooler (Cummins OEM), heat exchanger (Cummins OEM) and the exhaust aft of the Turbo, because the old exhaust elbow was badly corroded and too close to the sea water level. This means that that everything is clean and there should not be any restrictions in the system.
The new exhaust piping is very much according to Tony’s advice.
This means I have a dry pipe raising the exhaust about 30 cm over the sea water level and the new spray head is attached to that on the down side of the dry pipe.
The spray head is a 3,5″ AISI 316 straight pipe (about 25 cm long) surrounded by a 5″ AISI 316 water jacket.
The inlet to the spray head is 32mm (same as all raw water tubing on the engine) and there is currently 18 8mm holes through which the raw water discharges into the exhaust hose. There was first 12 8mm holes drilled symmetrically around and later I drilled 6 8mm holes more on the “aft” side (assumingly hot side)of the spray head. Regarding the raw water discharge holes I have tried to adapt to the Cummins installation manual that followed with the boat. According to that I should have a minimum of 9 8 mm holes for the 6BT.

The problem I have is that the exhaust hose gets too hot (100-130 degrees centigrade) about 1 1/2 foot from the spray head outlet. The hose is perfectly cool up to that point.

I added a Vetus mixer ring (https://www.vetus.com/fi/spare-parts/exhaust-systems/mezclador-para-escape-6012.html) into the exhaust hose just after the spray head outlet and that clearly improved the situation, but it is still too hot. The outlet from the spray head is for about 1,5 foot in an angle of approximately 45 degrees from vertical and after that it makes a bend and continues more or less vertical before it raises maybe about 6″ before turning down and exits just at the sea water level (half exit under the water and the other half above the water line).
I could also see from the old exhaust hose that it had been hot even with the OEM 90 degrees Cummins elbow used before and that was routed the same way as now except that the first part after the exhaust elbow the angle was maybe 30 degrees from vertical and mounted lower (no raiser).

Now it is in my mind to try to get more raw water into the exhaust and also try some modifications of the spray head to improve the spray pattern.
In relation to more water the question is:
Does the Sherwood GC1 or GC5 physically fit the 6BT?
I know hat I have at least to adapt the hose sizes to match the 1 1/2 ” connection on the GC1 or GC5 compared to the M71 pump. It is fairly easy to enlarge the whole suction side to 1 1/2″, so that I could do provided hat the pump fits under the injection pump and goes clear of the engine bracket.

Topic

[Kjell Lindroos]

I will make the modifications as you advice during the winter, but it will take until maybe April before I am really able to verify the result. That is when the water normally is open again after the winter.
I will post an update of my final mixer design and information about the result when I am that far.
Thank you for your advice and effort.
I think this is a superior forum with a lot of fact and experience based information and I appreciate that.
BR
Kjell

[Tony Athens]

Look at the very crud picture/idea –Since your water injection is totally safe, basically I’d weld up most all of your existing holes–Leave maybe 4 open max ( or none at all) and move the holes to the inside to spray the water so it mixes with the gases.. I’d use lots of 1/4″ holes — Done right, that should solve the issue. It would be nice to see about 1-2 PSI of water pressure at cruise RPM inside the mixer chamber. I am sure you have none now

[Kjell Lindroos]

Thank you Tony.
I know it states somewhere under tonys-tips that a steep downward slope is always better.
Is that always true and how should the spray holes be in that case. Is mine too steep?
The angle is fairly steep (now when checking it up, maybe 60-70 degrees from horizontal), but there is definitely a slope. I apologize, but I noted I accidentally stated from vertical in my original question.
The hot spot in the exhaust starts about where the hose turn to horizontal (or almost horizontal) and that is at the point where the gray hose attaching band (do not know the correct term in English) is in the picture.
The hose is hot from that point more or less as long as it is visible in the picture.
After that it cools down.
Best Regards
Kjell

[Tony Athens]

It appears the mixed is basically pointed vary close to straight down?

[Kjell Lindroos]

Hello from a frosty Finland.
Minus 6 degrees centigrade now in the morning (Monday).
Attached are pictures of the overall installation as well as the spray head discharge side.
The top of the spray head is where there are more holes.
Like I said in the original long explanation of what has been done, everything is brand new (replaced during the last 3 months, by myself) on the seawater side, so there are no blockages.
I am pretty sure the problem has to do with the spray head design and the spray pattern like Tony says.
I though also think that the raw water pump capacity is quite close to the limit of what is needed.
The engine itself runs perfectly in regards to temperature(80 degrees centigrade even if the sea water temperature was up to 25 degrees last summer and the outside air temperature was up to 35 degrees centigrade), so the problem is just the exhaust.
There is also no space for any type of muffler and this is also one reason why I think about more water (to possibly get some more noice silencing).
I will take the boat out of water now on Wednesday this week, because the winter is approaching.

[Tony Athens]

Donald, plugging holes is a good idea, but what you really want to do is look at the actual elbow orientation and mark the top.. Then, leave just 2-3 open at the bottom and then plug all the rest up t0 90 degrees or so. Then a couple of more after skipping 1 or 2…… Leave it all open at the top.. This does 2 things–It pressurizes the water in the mixer and forces all the water to the top so even at low RPM’s so the water falls thru the hot gases.. Been doing this for decades.. All our “flare head sprayer diesigns” use this same principle. The pic attached is from 2001.

[donald roth]

I’ve found that older 6B’s with the Sherwood 1 1/4” pumps often suffer from hot spots on the exhaust tube beyond the shower elbow due too too little water flow to keep the elbow entirely flooded.
First insure that the entire raw water system is clean and healthy.
Plugging every third hole in the shower head may create enough back pressure to fill the elbows water jacket, keeping it cool all around.
Experiment with epoxy putty for filler, you can always drill it out if you don’t get the desired results.
The better solution is to get the Sea Max pump and upsize the plumbing.

[Tony Athens]

Post pictures of all/everything…..

Yes the GC1 will fit (1.5′ hose though) but your issue is mostly your mixer design..

[Author]

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