Black Smoke Perkins M30

[sam_novotny]

Noticed this morning that then engine would no longer rev above 2400rpm (under power) thus boat speed did not increase, but produced masses of black smoke. It stars fine, idles OK at 950rpm and seems to run OK up to 2000rpm. Posts seem to suggest blocked air intake or fouled prop. Initial cursery inspection didn't seem to indicate blocked air intake (filter changed circa 50 hours ago) and the propshaft turned easily by hand as normal.

Not used the boat much over winter, probably no more than 5 hours running time since September 03. Approx 30 minutes run last night at 1800rpm charging batteries. Noted raw water intake all but blocked this morning but engine did not overheat and impeller intact.

Suggestions greatfully received.

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[sailorman]

if the intake was blocked its a good chance prop fouled

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[rich]

Is the hull clean?

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[sam_novotny]

No the hull is not clean. Although it has self eroding Micron CSC antifouling and the hull didn't appear to have too much 'growth' particularly after being used at Easter and again this weekend. Did notice though that the log was registering very low speeds through the water for given revs, typically with new antifouling I get 4.0 kts at 2000rpm and this weekend about 2.7kts. Thought perhaps some fouling around the log.

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[oldharry]

The prop may be easy to turn by hand but still fouled. The indications are that you have something on it which is fouling the blades and absorbing power, but not jamming the shaft at lower speed or on hand turning.

Does the engine rev normally out of gear? If not, then the engine has developed a fault. If it does then the fault is in shaft/prop.

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[brianhumber]

Any increase in resistance from fouled hull and prop will means increase in power is needed from engine to reach same hull speed. When the required power is greater than the engine can produce it cannot reach full revs, the reduced revs mean less air for combustion and the unburnt fuel is seen in the exhaust as black smoke.
Solution - lift, scrub and all will be well.


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[dickh]

This is possibly due to blocked fuel filters or a blocked up Exhaust water injection Elbow. Firstly check the exhaust elbow, but REMOVE it completely to have a good look at it. Unblock or renew as necessary(mine had only a small contorted hole up the middle and my friend had the same) - doing this first means you don't have diesel all over the place initally......
If the elbow is OK then check the fuel filters are not blocked and change if necessary.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Stemar]

Have a look at your prop and the bottom of your hull.

I did my Snapdragon over the weekend. Top speed going onto the scrubbing bay .5kts, engine (aged MD1) smoking like fury and maybe 800rpm flat out. 8ins of Cr*p all over and I couldn't even see the prop!

After 2hrs with a jetwash and a coat of antifoul, top speed 4kts plus and max revs a lot more without the smoke.

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[davidparker1]

I had exactly the same problem with my M30 a few years ago. It transpired that the exhaust elbow was blocked with salt and carbon deposits. It required removal to find and remove the obstruction. If this is your fault I would also recommend that the injectors are removed and checked for local overheating. I would add that I took many hours and much anguish to discover, what I consider to be, an obscure fault. I would be interested if this was the source of your problem when you find a resolution.

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[sam_novotny]

I am assuming (not having a manual at hand) that the exhaust 'elbow' that pepole refer to is the thick rubber hose that leads from the silencer in an upside down u-shape to the skin fitting. I assume also though, that the blockage (if there is one) could actually be anywhere between the exhaust manifold and the skin fitting, perhaps in the silencer itself if it has some trap there. By the way, the boat is a Moody 336.


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[davidparker1]

The blockage could be anywhere in the exhaust system. I my case it was in the cast METAL elbow where the cooling water is injected into the exhaust system. It is easily removed by undoing 4 bolts securing it to the heat exchanger assembly and undoing the jubilee clips holding the heavy rubber exhaust hose in place. I trust this helps.

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[sam_novotny]

Dear All,

whilst I haven't conclusively proved that his is the fix, reason being that I haven't refitted it because I haven't got a new gasket, but the exhaust 'elbow' was all but blocked by build up of carbon (or whatever it is). From what is normally 1.5" bore exhaust pipe was down to about 1/4". This possible fault was suggested by a number of people on this noticeboard. It's a wonder that the engine even ran and didn't overheat. Boat comes out the water in a few weeks time so will inspect the prop etc.

Thank you all very much for the suggestions!

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[brianhumber]

A blocked exhaust would certainly stop the engine clearing all the combustion gases from the cylinders at higher powers therefore it could not charge the cylinder with new air enough for the next cycle. If this was not happening last year and you have only run 5 hrs since maybe worth looking further as you should not block an exhaust up on low load in 5 hrs.

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