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Perkins 4-108 RPMs and Speed Achieved

D

dicklatour

Dick Latour
<div>I am interested in knowing what is the Max RPM for this engine
and at what speed & RPM do most owner's usally cruise. I have
found that about 1700 to 1800 RPM seems to be a speed at which
the boat moves well and the engine does not seem over tasked. I
am still working on the calibration of my knotmeter but my speed
through the water is believed to be about 6.4 to 6.5kts. At 2000
RPM the engine exhaust starts to smoke.I am running with the three bladed prop that came with the boat
from the factory. No modifications have been made to the
drivetrain.
</div>
 
I run 1800 to 2000 RPM and run 6.8 to 7.0 knts. Perkins book indicates that the engine can run at 3000 RPM continous and 3500 RPM intermitant ie 45 min out of an hour. It has been sujested to me that the boat is over proped and there is to much load on the engine. That was my query below on prop size. I didn't get much of a response. Hope you do better. My prop is three blade 16"by 11.

 
When we bought our 82 M383, our surveyor suggested that the prop was oversized because the engine would start to smoke over 1800 RPM. So we had the prop re-pitched and re-diametered to a 15X10. The result is that we run about 6.5 knots at 2000 RPM with no smoke. In hindsight, we probably would have just had the prop re-pitched because of the higher fuel consumption and greater noise at cruising speed. By the way, our fuel consumption is approximately 0.7 gallons per hour at 2000 RPM. Keep in mind that to get the prop off, you either have to remove the rudder (which is what we did), or pull the transmission. Good luck.
 
I have the factory installed running gear w/ a 16X11 prop on a 384, sail #39. I run at 1800-2000 rpm at about 6-6.5kt and burn about .6 gpm. I don't begin to smoke until over 2400 rpm, which does nothing good. I am satisfied with this arrangement, especially when I have had to wiggle off of a sand bar (I ran aground once). I am no expert, but I believe if you reduce prop pitch, you sacrifice torque. When I changed the alternator last year, I calibrated the tach, so I believe the above numbers are real.
 
Bud,
What procedures were used to calibrate your tach? I'm quite sure mine is out of calibration, it sticks and needs replaced anyway.
Fred


 
It appears that your numbers are pretty much in there with serveral others. My M384 hull #9 seems to feel & sound best at 1600 to 1900 rpms with speed approching 7kts on the upper end depending of course on sea & wind conditions. I haven't noticed any smoking at 2000 - 2200 rpms but I get a little vibration and my speed really doesn't increase much with the stern tending to sink a bit. I think that must be the hull speed.
good luck and happy sailing
 
I have a 1978 with a Perkins--it was a special order back when Yanmar was standard. The standard advice is that you should be able to run the engin up to something close to its max rpms, for emergencies, for instance, to get the full hp and torque. Or at least 80% or something. If you are smoking at 2400, you probably are over propped. I do not know my prop diameter and pitch--never looked, but I can go up to 3300 or so. I run at 2000 to 2300 to get over 6 knots and I have had crew impatient pushing up the Columbia River run her at 2500. 2000 and over, the engine is loud. I expect I will cruise lower, and live with lower speed, just for sound. So, it is your choice. You might seek advice on prop size from an expert. Dave Gerr wrote a book about it, for instance. What I would like to know is what folks have done to deaden sound. I have pretty good insulation material, but it is hard to insulate everywhere under the cockpit, and the sound is still very loud. I had hoped when I moved up in boat, I would move down in noise. Seems impossible to block all the avenues, unless, perhaps, one has a center cockpit designed boat. Suggestions?
 
I used an electronic tach with a strobe light and plotted the indicated rpm vs the electronic read out (two man job). The indicated rpm was a constant 20% lower than the electronic rpm. Since I didn't, and still don't know how to adjust the indicated readout on the tach, I mentally add 25% to the indicated and that gives me the actual. This came about as a result of putting in a new alternator which had less poles than the original. I would be interested to hear if anyone knows how to adjust the original tach.

 
<div>I had roughly the same experience with the 33 yanmar tach. However, I'm not sure it is an original tach. I checked it with a strobe tach and found it was off by almost 600 RPMs at what should be it's cruising RPM ie. the tack read 2800 and the actual RPM was 2221, quite a difference.In the just a note department.... You can check the actual RPMs without a strobe tack. However you can only check one or 2 fixed RPMs (1800 and 3600). All you need is 110volt fluoresent lamp. The procedure is fairly simple. Put a pieace of tape on the face of the large drive pulley. Hold the lamp in front of the pulley. Turn the engine up until you see 4 marks of the tape standing still on the face of the pulley. The engine is turning 1800 RPM. If your engine will turn 3600 RPMs you can get a second point of reference. 2 marks will stand still on the face of the pulley at 3600. The procedure is quite accurate because of the 120 pulses per second of the lamp. It's not an end all do all test but it will give you a point of reference for your tach.
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I changed alternators a year ago, and had the problem of an erroneous tach. You might try resettung the dip swithes on the back of the tachometer...I was told that the adjustment could be made be a pot on the back, but a few phone calls led me to the dip switches...trial and error, but had a good end result.

 
I've pulled my fuel injectors, to have them serviced, but can't find a reference in the service manual for torquing them down. Does anyone know what the torque specifications are?
Thanks,
Mike

 
I am the original owner of Papillon M384. We run the Perkins at 1800/2000 RPM speed at 1800 is 6.5 knots and most of the time the GPS agrees.
Just found this site and think its great.
Guy
 
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