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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.