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Discussion Starter #1 (Edited)
Calling all diesel experts...

I'm not very knowlegable about diesel engines but I have read a number of posts on 'black smoke' so far on this site and others.




I have read the basic symptoms from a number of sites but http://www.catalina320.com captured it quite well:
Black Smoke is caused by partially burned fuel. When the fuel/air mixture increases there is insufficient oxygen present in the cylinders to complete the combustion process. Large quantities of carbon are then produced which appear from the exhaust as minute black soot particles. Engines with turbochargers have additional sources of black smoke.
Black Smoke Insufficient Air:
Causes: Air intake filter clogged [2] - Air intake restricted [3] - Exhaust restricted [3] - Leaking inlet or exhaust valves [4] - Poor engine room ventilation [4]
Black Smoke Excessive Fuel:
Causes: Defective injector(s) [1] - Incorrect injector nozzle [3] - Injector pump incorrectly set [4] - Low fuel grade [4]
Black Smoke Engine Overload: As load increases the governor senses the slight decrease in RPM and adjusts the injector pump to deliver more fuel. If the engine becomes overloaded then the increase in fuel does not increase RPM and no extra air is being sucked into the cylinders. Net result - soot:
Causes: Boat bottom dirty [1] - Propeller dirty/fouled [1] - Engine alignment incorrect [2] - Propeller incorrect [3] - Transmission incorrect ratio [3]
So here are my specifics:
1986 Pearson 28-2 which I've owned for 2 years. No problems thus far.
Yanmar 2GM20F, original engine, unknown hours, ran well until today
Last fuel filter change in fall before hauling for winter

Symptoms today:
Max RPM I could achive under load was 2700 (that would only drive the boat at aprox 4.5 knots), normal max rpm under load is over 3100 rpm (which will normally drive the boat at just over 6 knots)
At 2700 RPM thick black smoke would come out of the exhaust, if I backed down to 2500 RPM smoke went away and speed woud drop to 4 knots or so
Plenty of water in the exhaust
Back in the slip, in neutral I could max the RPMs out at 3400 or even higher with no black smoke

Other info:
Not had this problem before and there has been no change to prop or other engine components.
I can't imagine the bottom or prop are fouled since it was cleaned, scraped and painted just before launch on April 15th or so of this year.

I'll be having a mechanic take a look at it but was wondering what troubleshooting steps and/or questions to ask the mechanic that some of you might suggest.

Anything jump out at you?


Thanks in advance.
 

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The end of your inserted article probably holds the clue - I reckon your prop has something wrapped around it. That would account for the lower than normal RPM, the lack of smoke when revving free, the rapid fall-off in speed at a lower RPM as well of course as the black smoke.
 

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Discussion Starter #3
Thanks Omatako.
I will check that. Also, you undersood correctly that there is no smoke revving free. I should have included that. I'll fix it in the orginal post.

Symptoms today:
Max RPM I could achive under load was 2700 (that would only drive the boat at aprox 4.5 knots), normal max rpm under load is over 3100 rpm (which will normally drive the boat at just over 6 knots)
At 2700 RPM thick black smoke would come out of the exhaust, if I backed down to 2500 RPM smoke went away and speed woud drop to 4 knots or so
Plenty of water in the exhaust
Back in the slip, in neutral I could max the RPMs out at 3400 or even higher with no black smoke.
 

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Have you been using the boat regularly since launch in April??

When was the last time you had it out, and engine ran well?

If it has been a month or so, you may have enough growth on the hull and prop to account for this??
 

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Discussion Starter #7
Update and Resolution

Problem Solved.

Thanks to all who posted (Omatako, Northeaster, Bubb2, Davekanelavie), you were right on! Barnacles!

Although it will cost me the price of a quick haul and scrape, I'm very happy to find it was nothing serious. As I stated, its only been in the water for 10 weeks. My marina guy told me they coat the prop/shaft with a spray on anti-fouling agent but didn't know the name of the product. He also said this year has been a bad year for barnacles in my area, he's had to haul quite a few boats. I'm going to have to try somehthing new next year and I'll have to try to use the boat more so those critters won't be able to hang on as well.

Here's what I found this morning.



Those critters must get dizzy!



The bottom paint didn't look bad at all. Was redone this winter.


I told my wife, we'll just have to use the boat every weekend. It will be cheaper to try to keep the barnacles off a spinning prop than to have to have it hauled now and then.
 

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Yikes, thats not a drive train, it's a reef:laugher Poor little Yanmar! I've sometimes noticed that my motor (same one) will smoke at 3000 RPM if I'm fighting a strong tide and/or headwinds. If I back off the RPM, it seems fine. The motor purrs at 3000 otherwise, so I assume it's not a prop issue. This has never made sense to me, as the motor shouldn't "know" what the opposing forces are. Right? They should simply make the boat go slower. Or, are the forces somehow "lugging" the motor? Hypothetically, if the boat was tied to the dock, shouldn't the motor turn effectively at 3000 RPM? Dock, line, boat and dock cleat failure aside of course:p Someone please explain:confused:
 

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I found a web site with the mainteance manual, mine is on the boat. It lists monitoring the exhaust colour and if it is black is says you are overloading the engine and this should be avoided as it will shorten engine life.

Diesels like to be worked but within limits. It also says if you are running for long periods of time at slower RPMs that every 2 hours you should rev the engine up several times to clear it out.

Web site can be found here
Yanmar Manual

Gary
 

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I found a web site with the maintenance manual, mine is on the boat. It lists monitoring the exhaust colour and if it is black is says you are overloading the engine and this should be avoided as it will shorten engine life.

Diesels like to be worked but within limits. It also says if you are running for long periods of time at slower RPMs that every 2 hours you should rev the engine up several times to clear it out.

Web site can be found here
Yanmar Manual

Gary
Yeah, I have the same manual and have read that. When it happens, it's pretty obvious it's not good for the engine. I simply didn't understand WHY it was happening. However, as I think about it more, I realize that the opposing forces probably ARE lugging the motor, as if I were going up a hill in too high a gear. Obviously, I can't downshift on a boat, so the only option is to decrease rpm. Although, that analogy doesn't really work, because reducing RPM in the same gear wouldn't work in a truck. I'm so confused:confused: ! Just when I thought I knew what I was talking about, I proved myself wrong. Hate when that happens!:laugher
 

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I'm suprised you didn't notice issues with backing the boat. I got a similar encrustation at the end of last season, just on my prop. The first symptom noticed was the boat wouldn't back up worth a hoot. That alone didn't cause the penny to drop, but when the performance going forward was not as expected, I immediately suspected a prop load of barnacles, ony because my slip neighbor had told me the same thing happened to him the year before when I had no problem at all on the other side of the marina.
 

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Yikes, thats not a drive train, it's a reef:laugher Poor little Yanmar! I've sometimes noticed that my motor (same one) will smoke at 3000 RPM if I'm fighting a strong tide and/or headwinds. If I back off the RPM, it seems fine. The motor purrs at 3000 otherwise, so I assume it's not a prop issue. This has never made sense to me, as the motor shouldn't "know" what the opposing forces are. Right? They should simply make the boat go slower. Or, are the forces somehow "lugging" the motor? Hypothetically, if the boat was tied to the dock, shouldn't the motor turn effectively at 3000 RPM? Dock, line, boat and dock cleat failure aside of course:p Someone please explain:confused:
Depends if you mean having the motor turning the prop when at the dock or running in neutral. If in neutral then it should theoretically run to it's max governed speed.
However in the context of turning the prop, forces come into play.
If you are stationary and turning the prop, then the blades angle of attack to the water are at maximum so it has maximum load and it's static (the boat not moving rpm will be lower).As the boat begins to move forward the props angle of attack relative to the water is decreased so the load on the prop is less and the motor can spin it easier, faster the boat through the water the lesser the AoA on the blades.
So if your are motoring into a headwind your boat speed will be less so the AoA will be greater.
For instance if I am motoring my boat and try to go to full power too early then I will get smoke but if I allow the boat speed to increase and I incrementally open the throttle I can achieve full power and no smoke from the engine.
Same with a propeller driven aircraft, on the ground your max static rpm will be lower then what you will achieve when you are flying. In an aircraft this effect is more easily seen as if you place the aircraft in a dive to increase air speed you can actually over speed your motor if you do not reduce power.

Mychael
 

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It seems the critters don't like the taste of zink
 

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For instance if I am motoring my boat and try to go to full power too early then I will get smoke but if I allow the boat speed to increase and I incrementally open the throttle I can achieve full power and no smoke from the engine.
I think this is also because you are dumping more fuel in the cylinders than can be burnt efficiently until the pistons get up to speed.

Same with a propeller driven aircraft, on the ground your max static rpm will be lower then what you will achieve when you are flying. In an aircraft this effect is more easily seen as if you place the aircraft in a dive to increase air speed you can actually over speed your motor if you do not reduce power.Mychael
Interesting. Good analogy, and it IS easier to visualize with an aircraft. So, with momentum, the force of the air/water pushing the front of the prop aids in increasing the RPM and reduces the load on the motor. Correct? Is this what you mean by angle of attack (as the pitch of the prop isn't changing, (with the boat anyway))? Makes sense, but I never thought about it (obviously, physics isn't my strong suit!).
 

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Interesting. Good analogy, and it IS easier to visualize with an aircraft. So, with momentum, the force of the air/water pushing the front of the prop aids in increasing the RPM and reduces the load on the motor. Correct? Is this what you mean by angle of attack (as the pitch of the prop isn't changing, (with the boat anyway))? Makes sense, but I never thought about it (obviously, physics isn't my strong suit!).
Think of it more in the way of sailing you have actual wind, what you get if you feel the breeze standing on the shore and the apparent wind you get when you are sailing, which is a vector of the wind from it's true direction and from what you create by your own forward movement.
So, if you prop is turning (under engine) but your boat is not moving through the water then it's leading edge of the blades is getting maximum resistance from the water, trying to "cut" the water if you like.
As your boat makes forward motion the prop is "cutting" the water at a different angle (remember the wind vector analogy) and this reduces the load on the engine.
I've never had it explained to me in the terms of the air/water "pushing" the front of the prop, however that could essentially be correct, as when we stopped an aircraft engine in flight and then reduced our air speed, at some point the prop would stop "windmilling" and be stopped by the compression of the motor.. If we then dived to high speed we could usually (not always) forced the prop to begin rotating again, so I guess you could say it was pushing the prop.

Mike
 

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JSL3,
I have run into the same problem here in NJ. With all the rain we had in the spring the boat hung from the mooring under-used . The sun came out and I looked back to see that black exhaust cloud! I just figured it was time to don the wet suit and go for a swim. 5 minutes with the paint scraper and the problem was solved. A side note. My friend and I both being frugal, decided to test out a couple of the "urban legend" Anti foul remedies. He painted his prop with a Sharpie, I used Lanocoat. Somewhere on this site you can find someone extolling their virtues. Fugeddabout it! We will be doing manual prop cleaning every 5-6 weeks for the rest of the season. (not a big deal, really).
Bruce
 

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Discussion Starter #18
JSL3,
I have run into the same problem here in NJ. With all the rain we had in the spring the boat hung from the mooring under-used . The sun came out and I looked back to see that black exhaust cloud! I just figured it was time to don the wet suit and go for a swim. 5 minutes with the paint scraper and the problem was solved. A side note. My friend and I both being frugal, decided to test out a couple of the "urban legend" Anti foul remedies. He painted his prop with a Sharpie, I used Lanocoat. Somewhere on this site you can find someone extolling their virtues. Fugeddabout it! We will be doing manual prop cleaning every 5-6 weeks for the rest of the season. (not a big deal, really).
Bruce
I suppose my biggest problem was under use. Since the lastest cleaning I've been out 2 times (once a week basically) and all is well obviously. While the boat was out of the water two weeks ago I did try the 'urban legend' anti foul remedy of vaseline. No results yet due to the short time period.

Bruce,
When you scrape, do you just hold your breath or use other means of breathing under water?
 

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Yes, I just hold my breath. Sometimes if I want to be extra diligent I will use a snorkel and mask. Otherwise I just feel my way. Carefully! I guess gloves might be a good idea, but I do without.
B
 
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