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post #1 of 36 Old 04-08-2008 Thread Starter
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Max Cruising RPMs for Yanmar

I have a 1988 Morgan Classic 41 with an original Yanmar 4JHBE with 2,440 hours. It is in excellent condition, rigorously maintained and with no problems whatsoever. The rated horsepower is 44 @ 3600 rpm. Are there any opinions on a safe, long-range maximum cruising rpm for this engine? My S.O. insists I not exceed 2700 rpm and I can't see crossing the Gulf Stream from Miami to Cat Cay at a VMG of 2 knots if we have to motor. Thoughts appreciated.
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post #2 of 36 Old 04-08-2008
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You should be at about 80% of max RPM. If max is 3600, then you need to be about 2880. That should be more than enough to push you at hull speed.

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post #3 of 36 Old 04-08-2008
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be certain that the RPM / tach guage is reading accurately. most guages need to be adjusted while using a timing device.
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post #4 of 36 Old 04-08-2008
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Forever Cruising.....

NOLAsailing gave you excellent advice. Provided the engine is operating well and taken care of, 80 to 85% of max RPM is often recommend for a Yanmar diesel (at least mine).

If you have any concerns, give Yanmar a call and they'll advise you in what's best for your motor.

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post #5 of 36 Old 04-08-2008
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In general most Yanmars operate at cruising at 2300-2500 RPM - anything above and beyond will just burn more fuel without any truly appreciated returns in speed.

-- Jody

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I have a Yanmar 4JHE and regularly motor at 2700 to 2800 RPM.
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post #7 of 36 Old 04-08-2008
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I had one and cruised at 3000 all the time with no ill effects and this was the RPM recommended to me by maxboring (the Yanmar distributor) in a seminar.

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Quote:
Originally Posted by artbyjody View Post
In general most Yanmars operate at cruising at 2300-2500 RPM - anything above and beyond will just burn more fuel without any truly appreciated returns in speed.
It's not just about speed. It's about doing what's mechanically best for the motor. Under-revving a small diesel has a number of ill effects.

-Jason

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post #9 of 36 Old 04-08-2008
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Quote:
Originally Posted by artbyjody View Post
In general most Yanmars operate at cruising at 2300-2500 RPM - anything above and beyond will just burn more fuel without any truly appreciated returns in speed.
Jody...I can assure you that I motored appreciably aster at 3000 RPM's than at 2500...and at considerably higher cost in fuel. The tradeoff is an individual choice...and motoring on the ICW for 8 hours rather than 10 hours was often a good trade off for me. Doesn't matter much in and out of harbors buton long motoring days...that extra 1/2-1 knot can be quite important.

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Quote:
Originally Posted by camaraderie View Post
Jody...I can assure you that I motored appreciably aster at 3000 RPM's than at 2500...and at considerably higher cost in fuel. The tradeoff is an individual choice...and motoring on the ICW for 8 hours rather than 10 hours was often a good trade off for me. Doesn't matter much in and out of harbors buton long motoring days...that extra 1/2-1 knot can be quite important.
Hence why I stated the rpm value as generally speaking But good to know...and yes always a trade-off... I probably am more like you as time motoring is of the essence - when sailing - don't care

-- Jody

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