Smoky Farymann - Overpropped?

[clausont]

I have the new flex coupling in place now and have run the engine in gear for about an hour. Granted, I am running it against the dock lines which may load the engine slightly more than if the boat were able to move.
What I notice is that at around half throttle (perhaps even a little less) I am starting to blow black smoke and leave a sheen on the water from the exhaust.
I have no idea what the engine rpm, shaft rpm or reduction is as there is no prop and I have found no information on the transmission except that is is supposed to be a "Nanni" transmission.
If I remember correctly, the prop was a 2 bladed 12x6. I may be wrong about the prop, but I am pretty sure that is what it is.
Where do I go from here as far as figuring what the problem is?
Or is this a normal Farymann situation?
12hp Farymann single cylinder (A30?)

[Chief Engineer]

On Tugs we called this dead pushing. If you load the engine like this (any engine) it will smoke

[CSY Man]

What is the RPM tied to the dock?
RPM under way at the same power setting?

Tied to the dock one should get 90% of max RPM. (Clean prop of course.)

Black smoke to be expected as the engine is a bit over-loaded, the black stuff would be un-burned fuel...Soot.

[Brent Swain]

If, underway , you can give her full throttle, then back it off slightly and hear the engine slow down slightly, you are probably not overloading her. If you have to back the throttle off a long way before the engine slows down you are probably over propped.

[clausont]

The one time so far that I motored her along underway, the engine was not warmed up well, but still blew quite a bit of black smoke at higher throttle settings. The prop, shaft and bottom are clean (this was on the way from the travel lift to the slip about 1/2 mile away). Again, I have no idea what the rpm is - I have no tach. That is something I would like to add, but not sure how yet to do that on a Farymann - low priority anyway.
I felt at the time that the engine was overloaded even underway, but then again I am not sure. We used to have a small compactor called a "Rammax" that used the same engine and it always blew black smoke no matter what.
Maybe my first thing to do would be to install a tach and go from there?
BTW -I understand pretty well the characteristics of diesel engines - I ran heavy equipment for about 25 years before moving into the technology field.
Thanks

[David M]

Definitely get a working tach first or get an RPM meter that you can shine on your flywheel or anything connected to the crankshaft.

A boat is effectively over propped when it it tied to the dock and not making way. So this is not an effective measure of engine health or whether or not you are over propped.

You need to do the same thing again but with the engine fully warmed up this time. Also, you never want to put a full load on an engine that is not fully warmed up.

It could be one of two potential problems. The engine is incapable of full RPM because there is something wrong with the engine or as you guessed, the engine is over propped...or both. If you are getting clouds of smoke even when the engine is warm and there is a light load, then there is something clearly wrong with the engine. A puff of black smoke when running the throttles up quickly or some black smoke when the throttle is two-blocked, is normal for older non Tier-2 diesels.

I would do all the basics like change the filters and change the oil and tranny oil and then have a marine diesel mechanic who knows your type of diesel take a look.

David

[clausont]

We spent three days last week on the boat (great fun - loved it! ). During this time, I ran the engine for several hours total. During the time I was running it one day, I had it fully warmed up and we were motoring freely in the bay. I started running the throttle up slowly as I let the boat build speed. I did not start getting any smoke at all until about 6 1/4 knots. I was at full throttle at this point. I ran it at full throttle for maybe three or four minutes (I generally don't like to run an engine when it is blowing black smoke) and the knot meter topped at 7 knots. Backing the throttle back down it was running quite comfortably at 6 knots with no smoke at all. I still don't know what the rpm was, but I will be installing a tach at some point.
So I think that the engine is running well forr the most part and the problem was mainly that I was running it where the engine could not unload.

[Chief Engineer]

7.22 Knots is the theoretical hull speed for a 29 footer.
1.34 x square root of the length water line.

the LWL for a 29 footer might be 27'....6.9 Knots....

[Alan Wheeler]

Remember that Logs may not be accurate and even GPS has to have currents factored in. So 6.25 kts could be what is indicated, but may not be the actual speed. A distance over time test is required to give you a good accurate speed.

[clausont]

Good reminder Alan. I will remember that for the future. I have not traveled enough distance to do a reasonable time/distance test. My father showed me when I was a kid how to drop a small stick off the bow of the boat when traveling and time it until it passed the transom to get a rough idea of speed traveled through the water - but somehow I don't think that would be very accurate with such a short distance traveled among other error factors

[Ex-Calif]

How well does she accelerate?

If we push the throttle to the stop on our boat from a standstill it will blow a little black smoke. It accelerates to about 6 kts in about 10 seconds and the smoke disappears as we pass through about 3 kts.

If we accelerate slowly we don't get any smoke.

Your boat is probably heavier but it should accelerate smartly if it lags you may be overpropped. Also even without a tach you should be able to hear the RPM catch up as the boat accelerates.

Try a fairly brisk throttle advance and take note of acceleration and RPM noise. RPM should build slowly at first and then build rapidly. If it is making full RPM it will probably sound like it's making too much. Most people don't push their engines to the max and aren't used to the noise level.

[Southern Star]

Clausont, I had a Farymann 2 cyl. on my Bayfield 32 with hydraulic drive and the factory prop and, despite adjusting the swish plates in the hydrualic pump for proper load, she always left some soot on the transom around the exhaust. Not clouds of black smoke, but enough to leave deposits on the transom, as indicated.

Despite that, she ran great for the 3 years I owned her (and to my knowledge, has in the 5 years since for the current owner). Pretty tough engines.

Brad