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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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Old 06-06-2013
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Yanmar 2GM20 (J) Achieving Design RPM

I have a FP catamaran model (35') diesel powered with YANMAR 2GM20 (FC)s (via SD 20s). I have 16 X 12, 2-blade props and am only getting about 3,100 rpm at full throttle and the design max rpm for the engine is said to be 3,600. The 16 x 12 props were measured but were really 16 x 11s. They were re-pitched to 10s hoping to get close to the 3,600 but only saw a modest (50 rpm) increase. What would you suggest to achieve the design rpm?

Last edited by dclery; 06-06-2013 at 10:21 AM. Reason: Engine model suffix was incorrect/incomplete
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Old 06-06-2013
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Re: Yanmar 2GM20 (J) Achieving Design RPM

If you are happy with the boat speed, I wouldn't do a thing.
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Old 06-06-2013
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Re: Yanmar 2GM20 (J) Achieving Design RPM

I second that
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Old 06-07-2013
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Re: Yanmar 2GM20 (J) Achieving Design RPM

I third that.

If you are still determined to get more RPM, you might confirm that the throttle cable is providing the full range of motion. You could pull the cable off and have someone open the throttle up by hand to confirm it's not a cable adjustment issue.
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Old 06-07-2013
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Re: Yanmar 2GM20 (J) Achieving Design RPM

Are you sure that the tach is accurate? Get a digital tach and check it.

I know that mine is way way off (2000rpm on the tach means my engine is turning around 2700rpm). I have a 2GM20F.
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Old 06-08-2013
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Re: Yanmar 2GM20 (J) Achieving Design RPM

I second the idea of checking your tacho. If the 3100 rpm is accurate and if it is not showing signs of being over-loaded at full throttle, like blowing smoke and raw diesel out the exhaust, AND if you are happy with boat speed, accept it.
Much less than 3100 at full throttle would not be good for this engine long term.

With my displacement mono-hull, I find that although it will turn 3200 to 3300 RPM at WOT, boat speed does not improve enough to measure (maybe a quarter of a knot) above 2800 RPM, which is what I would expect. The engine seems to have a cruising 'sweet spot' at 2200 to 2300 RPM so that's where it spends most of its time. Boat speed is about 1.3 knots below maximum at that. I do run it up to high power for a few minutes every hour or so as Yanmar recommends.

Last edited by arvicola-amphibius; 06-08-2013 at 03:03 AM.
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Re: Yanmar 2GM20 (J) Achieving Design RPM

And keep in mind that 3600 RPM is the maximum rating on the GM series, only good for 1 hour. 3400 is the continuous RPM rating.
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Old 06-19-2013
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Re: Yanmar 2GM20 (J) Achieving Design RPM

I have a 2gm. Cant seam to get it above 2800rpms in gear. It likes to run ar 2100. It will not take gear above 900rpms. I think my tac is wrong? I cant prove it. I dont want to buy a dig tacometer just to test it. Cheep I guess. I do push it hard coming back to the dock each time out. Were I know its working hard. I see some smoke, but not bad... The prop I understand has a lot to do with it.
here is the prop on mine. it folds. not its the correct prop for the boat. It dont work in rev much at all



15DX9P2

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Old 06-19-2013
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Re: Yanmar 2GM20 (J) Achieving Design RPM

Correction to my last post, I just looked at the tag on my Yanmar.
it is a 2GM 13 with a continuous duty rating of 3400 rpms
Is this a regular engine? is there a 2gm 13?


[IMG] photo Yanmar.jpg[/IMG]

Yes I have cleaned it up and it will soon be repainted?
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