Sooty transom

HiDHo said:

Richard, your peak torque for you JD is 1800 rpm, I'd clean the stern and try running at 1800 rpm and see if it still smokes. When you run at near max rpm pushing a 54' hole in the water your going to smoke a little. Be interested to see what the speed difference would be ?

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Thanks - I do run the engine at 1600-1800 rpm as my normal cruising range. I took it up to max RPM in response to the question asked in post #3 on this thread:

twistedtree said:

You will always get some amount of soot, but how much is too much?

The first, because it's easiest, thing to check is the propping on the boat. Look up the rated full throttle RPM for your engine, then see what they actually turn at full throttle. It should be a couple hundred RPM over, let me repeat OVER, the rated RPM.

Chances are very good that you will be below the rated RPM indicating overloading of your engine, and resulting excessive soot. The solution is to have your props repitched, which sounds much more drastic than it really is.

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On your speed question I make 7.9 kt at 1800 rpm using 1.4 nmpg and make 9.4 kt at 2200 rpm using 0.9 nmpg. At 1600 rpm I'm making 7.4 kt using 2.2 nmpg (that's the max speed for going to Hawaii).

Richard

Ski in NC said:

...
If the OP can't make full turns due to dirty bottom, that will certainly do it.

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I'm scheduling a bottom cleaning and we'll see if that helps.

Richard

Soot from overloading is most common on fish killers as they run WOT for a min to get up on the plane.

Cruisers that are not visibly smoking should remember there are loads of combustion by products in the exhaust , some will discolor paint or gel coat. This does not mean a bad engine.

Chemically removing the discoloration might be done at the expense of some of the surface being cleaned.

Toilet bowl cleaner is common.

Ship Shape and Bristol is fine , but there might be a price.

Britannia said:

Interesting. Let me know how it goes.

Here's my transom after about 6-7 hours of motoring - it was clean before the trip.

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The soot pattern seems to indicate the air flow around the transom is stalling in that area and do the door builds up there.

Sea Shield doesn't make an exhaust remover per say that in aware of. But they do make a sealant (Exhaust Guard) that soot doesn't seem to stick to well that makes it pretty easy to wash off.

I would not use Magic Erasers on a painted hull nor on a polished and waxed gelcoat hull that is in good shape. They will dull/scratch a polished surface.

Toilet bowl cleaner will remove the ice tea colored stains from tannic acid. But not do much to remove soot from what I've seen.

restricted air intake (air filters, ER intakes) as in first post
Over propped or dirty prop/bottom not reaching wot rpm
injectors and/or valve adjustment

If your air filters are clean run the boat with a engine room hatch open and see if that cures it.

My 6 cyl Volvos need all these tweeks at 105% or I get soot on my stern, canvas, cushions... what a mess. I have done everything from prop speed to new turbos, new injectors, air seps, and on and on. She turns up 50rpm more than spec and I still get some sooting after 4 hours of running. I have not tried running with the hatch cracked open a bit which is my next step. All this work has improved the exhaust significantly but it is still not right.

dbltime said:

restricted air intake (air filters, ER intakes) as in first post
Over propped or dirty prop/bottom not reaching wot rpm
injectors and/or valve adjustment

If your air filters are clean run the boat with a engine room hatch open and see if that cures it.

My 6 cyl Volvos need all these tweeks at 105% or I get soot on my stern, canvas, cushions... what a mess. I have done everything from prop speed to new turbos, new injectors, air seps, and on and on. She turns up 50rpm more than spec and I still get some sooting after 4 hours of running. I have not tried running with the hatch cracked open a bit which is my next step. All this work has improved the exhaust significantly but it is still not right.

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Maybe it just is what it is. And they will never burn 100% clean.

manyboats said:

Our Willard has no soot at all. Only very slight smoke at start up.

However the engine was new less than 10 years ago and has less than 1000hrs on the clock. Propped to rated rpm of 3000.

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No transom either LOL

Tailpipes that submerge when under way seem to make more a mess than those that stay above water.

Your rated wot rpm could be 2300 depending on your hp. They built that model in several hp ranges:
154 115 156 22.7 2300
M1 158 118 160 23.3 2400
M2 176 131 178 25.8 2400
M2 178 133 181 26.2 2500
M3 200 149 203 29.4 2500
M3 201 150 204 29.6 2600


M4 225 168 228 33.1 2600

dbltime said:

Your rated wot rpm could be 2300 depending on your hp. They built that model in several hp ranges:
154 115 156 22.7 2300
M1 158 118 160 23.3 2400
M2 176 131 178 25.8 2400
M2 178 133 181 26.2 2500
M3 200 149 203 29.4 2500
M3 201 150 204 29.6 2600


M4 225 168 228 33.1 2600

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When I do a serial number search at the JD site, my 1996 engine shows up as a 6068TFM01. I can't seem find out exactly what that is from the JD site. Could it be a 6068TFM50 M1 rated engine? If it is then it's rated at 151HP and has a max RPM of 2300. It could be a 6068TFM75. The M1 rating makes sense (I think) given the expected duty cycle.

Richard

Greetings,
Regards post #18. I have it on good authority that: "...
the engine on that KK54 might produce up to about a pound of particulates every 5 hours of running and still meet EPA standards."

RT Firefly said:

Greetings,
Regards post #18. I have it on good authority that: "...
the engine on that KK54 might produce up to about a pound of particulates every 5 hours of running and still meet EPA standards."

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Fascinating Mr F! I think the airflow around my (non-) transom could be trapping a fraction of that one pound of soot and painting my gel coat with it.

Richard

While all of the issues noted in previous posts are valid. All diesels produce soot. Diesel does not work at 100% efficiency. That couple of points of inefficiency produces particulates in the exhaust. The air flow around the exhaust may suffer from the station wagon effect and stain part of the stern. In my own boat there is no visible smoke but there is a 20" circle of very light staining over 2' away from the exhaust outlet after a long days run. Being that far from the exhaust can only be accounted for by the air flow around my fantail stern. I have a plan to move the exhaust outlet next summer when she is hauled to do the bottom.

I had the same staining on two previous boats that also showed no visible smoke in the exhaust. I moved the exhaust outlet from the transom to the side on one boat and put a 2' FRP extension on the other and never saw another stain.