Sooty transom

Well I suppose this sounds like a personal problem. However, I have a dirty butt! Every time I go out the soot from the exhaust makes a mess on the gelcoat on that is hard to remove without a deep clean and some local waxing. My boat cleaning guy says most of the boats he works on don't have this problem - though one of them does.

Does anyone else have a similar problem? Could it be to do with the emissions from my engine being somehow out of whack? Or perhaps it's something to do with the airflow around my canoe stern? Old gelcoat? Or maybe all the other boats my guy cleans never leave the slip?!?

I'm interested in other people's experiences.

Thanks

Richard
Stillwater
KK54 #5

Soot in your exhaust means incomplete combustion of your fuel. Soot is just unburned carbon. Does this happen right after you have the bottom painted or cleaned. It may simply represent a dirty bottom causing excess drag, which makes your engine work harder to achieve speed.

Another possibility is that you don't have sufficient air flow to the engine. Low air flow can cause incomplete combustion. Check your air filters to see if they need cleaning/replacement. Also make sure there is sufficient airflow into your engine room. Diesels need a lot of air to run properly.

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.

Could well be you are over propped or have a fouled prop/bottom. Could also be a bad injector or two. Or , worst case, a cylinder or two with low compression. Has it always done this, including when you had it sea trialed and the engines surveyed?

I don't agree there should be some soot. And I speak as a Detroit Diesel owner.

Some great suggestions here - thanks!

I will check the max RPM next time I take her out.

It's quite possible that the bottom is in need of a clean - it's been a while

I've only had the boat since April and I'm not sure, but I think it seems to have gotten worse in the last few months.

Richard

twistedtree said:

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

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We are fortunate. Zero soot and it has been this way since new. Can't argue with any of the reasons cited though as to possible Britannia soot.

A few years ago I was curious as to innards of Cetek water lifts. After removing the exhaust hose I noticed large granules of carbon in the bottom. At that time I wondered if the Ceteks were acting as a scrubber. Just trivia but it did get me thinking ---

I had the same problem on my 38' Sport Fisher years ago. At the end of a hard days run, her bum was really sooty. I bought two FuelSeps from Walker Engineering, installed them and "poof" the soot was gone.

Walker Engineering - Home

How old is your fuel. Old fuel can produce soot!

Codger2 said:

I had the same problem on my 38' Sport Fisher years ago. At the end of a hard days run, her bum was really sooty. I bought two FuelSeps from Walker Engineering, installed them and "poof" the soot was gone.

Walker Engineering - Home

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Walt,

Thanks - I will look into these if other solutions don't solve the issue.

Richard

gehales said:

How old is your fuel. Old fuel can produce soot!

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I burned most of the older fuel on my trip from Ketchikan. At this point the fuel is no more than 6 months old.

If the air and exhaust at your transom station wagons back toward the boat there may not be much you can do about it.

Although I had a soot issue with the boat I'm currently running and for the heck of it I tried this,

http://www.westmarine.com/buy/star-brite--startron-diesel-additive--P006_186_003_508

and surprisingly it's made a very, very noticeable difference in the amount of soot on the transom at the end of the day. Info add about twice the recommended dosage.

As always with something like this, YMMV.

We also keep the transom coated with Exhaust Guard sealant which makes it very easy to wash off the soot.

https://www.sea-shield.com

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.

I think the key issues are covered by previous posts, reaching max RPMS is the key to knowing if everything is in order, and if you don't reach (provided to reached it at one time) then yes a host of things could be attributed to that, like fouled bottom, very pour fuel quality, injector issues etc.

We noticed after very long runs while using Valvetec fuel it greatly reduces residue on the transom, keep in mind we are a planing boat so running through a lot more fuel then say manyboats that uses a teaspoon every month! ;-)

twistedtree said:

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

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My last boat, with DD892TA's, left plenty of soot. In fact, if you looked carefully, especially when the boat was planing, you could see the exhaust trail behind the boat. That is typical for Detroits, especially after a few thousand hours. My transom always had soot, but it washed off easily (the boat was Awlgripped).

My current boat, with Cummins QSM11's, has never had visible exhaust under any circumstances, and my transom never has soot. The side of my boat got soot once, however, from the generator of a guy who side tied to me.

I once had a Defever 45 PH with twin John Deere 4045's. I also had a bad soot problem until I started using Soltron (aka Star Tron). It made a big difference and a very noticeable decrease in exhaust smoke.

In my area it is very easy to buy fuel with Valvtec additive added and that is what I use exclusively and I don't have a soot problem with my 2004 Cummins 8.3 engine.

MYTraveler said:

My last boat, with DD892TA's, left plenty of soot. In fact, if you looked carefully, especially when the boat was planing, you could see the exhaust trail behind the boat. That is typical for Detroits, especially after a few thousand hours. My transom always had soot, but it washed off easily (the boat was Awlgripped).

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The only time I had soot on the transom issue with my 8v92Tis was when I experimented with a higher pitch prop. Ended that experiment dang quick. Maybe the TA' are different, but I'd change that quote to "typical of very aged or poorly maintained or over-propped Detroits". As Bill mentioned some has to do with boat design, the motoryacht generating some amount of station wagon effect in a following wind. We'd get some exhaust smell, but no soot.

I was once told by a local boat detail guy that one should not wax the transom on a diesel because the soot attacks the wax quickly and makes it harder to keep clean.
And all diesels have soot in their exhaust.
I had that problem on my last boat. I think it was because it was fast enough to create the station wagon effect and the soot/water mix would come around and deposit on the transom.
I can't go fast enough for that effect on my current boat.

Will a diesel (mechanical or electronic) make smoke and put black soot on the transom if it has good compression and is propped to rated rpm?

I think it needs to be over fueled or have poor compression to soot the transom. Am I wrong? My own boat w about 900hrs on the engine has paint on the transom that isn't even glossy. Some PO applied it. It's never been over propped and operated almost always at 50% load .. 2300rpm. I've never cleaned the transom more than the rest of the boat and the rest of the boat has fairly good gelcoat.

Don't use wax, use something like Rejex or AwlCare.

jleonard said:

I was once told by a local boat detail guy that one should not wax the transom on a diesel because the soot attacks the wax quickly and makes it harder to keep clean.

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Maybe he meant it would stick to the wax like the dirty rain streaks do.

Otherwise that makes no sense. Because it's far better to have the wax/sealant trap the soot than it is the gelcoat or paint.

Check your engines troubleshooting section for engine smoking - black smoke.

Cat 3126 engines had a soot problem and it took cat a few years to fix the problem. What engines do you have?

Old deckhand said:

Cat 3126 engines had a soot problem and it took cat a few years to fix the problem. What engines do you have?

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Thanks to all of you for your continuing suggestions.

I have a 1996 John Deere 6068T.

To be honest the soot problem is not all that bad. I don't see any smoke in the exhaust even at startup. Just a noticeable area of dirtiness around the exhaust. I do wonder whether the shape of the stern is creating a low pressure spot there.

I'll take before/after pictures next time I go out if I remember.

Thanks

Richard

Richard,
I too have John Deere's. In my case the 6076. They don't produce noticeable soot, but after coming down from Canada (a 91 hour run) I did find that the transom was not as bright as it should be. the grey stuff doesn't want to come off with the light duty boat wash. I'm trying to find something that doesn't take too much elbow grease to remove it. I'll try some of the cleaning product mentioned in the thread--Capt Bill mentioned Sea Shield and they seem to have a soot remover that might work. I'll let you know how it goes, although it may be a while before I get back to the boat with the Holiday Season on....
curtis

Dawdler said:

Richard,
I too have John Deere's. In my case the 6076. They don't produce noticeable soot, but after coming down from Canada (a 91 hour run) I did find that the transom was not as bright as it should be. the grey stuff doesn't want to come off with the light duty boat wash. I'm trying to find something that doesn't take too much elbow grease to remove it. I'll try some of the cleaning product mentioned in the thread--Capt Bill mentioned Sea Shield and they seem to have a soot remover that might work. I'll let you know how it goes, although it may be a while before I get back to the boat with the Holiday Season on....
curtis

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Interesting. Let me know how it goes.

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

I did check my maximum RPM - it was 2300. I am not 100% sure what the max RPM for my 1996 JD 6068T is. I think it's probably 2400. Based on the earlier post I may be slightly over propped?

Richard

Dawdler said:

Richard,
I too have John Deere's. In my case the 6076. They don't produce noticeable soot, but after coming down from Canada (a 91 hour run) I did find that the transom was not as bright as it should be. the grey stuff doesn't want to come off with the light duty boat wash. I'm trying to find something that doesn't take too much elbow grease to remove it. I'll try some of the cleaning product mentioned in the thread--Capt Bill mentioned Sea Shield and they seem to have a soot remover that might work. I'll let you know how it goes, although it may be a while before I get back to the boat with the Holiday Season on....
curtis

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Try Magic Eraser. It's a very mild micro-abrasive that worked like a champ on my transom. Just a bucket of water and one sponge did my whole transom. Larger boats might need 2 sponges.

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 ?

Painting the hull (or transom in your case) a dark green or blue should make minor soot invisible. ... But why is your engine generating smoke? My JD is smokeless regardless of RPMs.

manyboats said:

Will a diesel (mechanical or electronic) make smoke and put black soot on the transom if it has good compression and is propped to rated rpm?

I think it needs to be over fueled or have poor compression to soot the transom. Am I wrong? My own boat w about 900hrs on the engine has paint on the transom that isn't even glossy. Some PO applied it. It's never been over propped and operated almost always at 50% load .. 2300rpm. I've never cleaned the transom more than the rest of the boat and the rest of the boat has fairly good gelcoat.

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MB, your engine is indirect injection aka pre-chamber, those tend to burn quite clean unless near overload.

On most other engines, they are direct injection and soot is more an issue. Not as much turbulence near injection site so mixing can be so-so or ok. Poor mixing of fuel and air, you get soot.

I have troubleshot a few of these issues: One thing I found with the turbo diesels is sometimes there were "bad" rpms and power settings to avoid. One boat with Detroits liked to run 1700 to be easy on his engines. I monitored on a test run and at 1700 they were dirty. Asked him to go to 1800 and they cleaned right up. That was the fix, 100 more turns.

On my boat, my 450 Cummins cruises nice at 1800. But it is a little sooty there. 1700, clean. 1950-2200, clean. But the boat likes 1800. So I compromise and run 1900. Almost clean there.

I could buy the 5-hole injectors for a boat buck and replace my 4-hole, but not worth it. A brush cleans the transom just fine, and in 500miles it is not horrible.

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