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Preferred cruising RPM ? #9576
05/24/10 09:52 AM
05/24/10 09:52 AM
Joined: Mar 2010
Posts: 93
PNW
lakesailor Offline OP
Senior Member
lakesailor  Offline OP
Senior Member
Joined: Mar 2010
Posts: 93
PNW
Just came back from our first delivery up the lake_roughly 5 hours in each direction. On the way up we cruised at 2200 rpm_..and on the way back we cruised at 2500 rpm to try something different.

Obviously different RPM's have a noticeable effect on the smoothness/vibration scale. Wondering what everyone uses for a preferred cruising RPM ?

Many thanks_.

Re: Preferred cruising RPM ? [Re: lakesailor] #9577
05/24/10 10:25 AM
05/24/10 10:25 AM
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,668
Portsmouth, RI
On Rhapsody with 2GM raw water cooled (13 hp), 2200-2300 RPM provides a good cruising speed, and the fuel consumption is good (about 0.3 gallons per hour). Vibration (resonance related) is also good in that range. When you kick the RPM up to 2800 fuel consumption is almost doubled with only a few tenths of a knot speed increase.

Re: Preferred cruising RPM ? [Re: Rhapsody #348] #9578
05/24/10 10:32 AM
05/24/10 10:32 AM
Joined: Apr 2004
Posts: 457
Highland Park, NJ
Steve Buzbee Offline
Senior Member
Steve Buzbee  Offline
Senior Member
Joined: Apr 2004
Posts: 457
Highland Park, NJ
I find that if I cruise for an extended period at higher revs (2800), the engine runs smoother as time passes. My understanding is that these engines like to be driven pretty hard. I haven't compared consumption and speed at different revs though.


Steve Buzbee
Blue Meanie J/30 #485
Re: Preferred cruising RPM ? [Re: Steve Buzbee] #9581
05/24/10 11:27 AM
05/24/10 11:27 AM
Joined: Mar 2010
Posts: 93
PNW
lakesailor Offline OP
Senior Member
lakesailor  Offline OP
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Joined: Mar 2010
Posts: 93
PNW
Thanks for the info. guys, much appreciated. I haven't tried 2800 rpm yet, however did find 2200 to be smoother then 2500 rpm vibration wise. Circe has fresh water cooling and a two blade Max-Prop. Using the GPS we were doing roughly 5.8 at 2200 rpm in no wind/flat water and averaging around 6.2 when we kicked it up to 2500 rpm (again based on GPS speed)

I will have to try 2800 to see what that is like from a vibration perspective.


Did some of the Yanmar's have different hp ratings in the J/30 ? I was assuming they were all 13 hp

Re: Preferred cruising RPM ? [Re: lakesailor] #9582
05/24/10 01:16 PM
05/24/10 01:16 PM
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,668
Portsmouth, RI
The 2GM original version was 13hp. There are also versions that are 15, 18 and 20hp. The 2GM20 is 20 HP and installed on some J/30s. if there is an "F" suffix (e.g. 2GM20F), the engine was installed as fresh water cooled, although some without the "F" suffix have been converted to fresh water cooling.

ps - Not all the Yanmars in the J/30 are 2GM series. They also installed 2QM and 2YM series engines.

Last edited by Rhapsody #348; 05/24/10 01:34 PM. Reason: more Yanmar engine types added.
Re: Preferred cruising RPM ? [Re: Rhapsody #348] #9585
05/25/10 05:35 PM
05/25/10 05:35 PM
Joined: Oct 2009
Posts: 381
Squamish, British Columbia
NaturalHigh Offline
Senior Member
NaturalHigh  Offline
Senior Member
Joined: Oct 2009
Posts: 381
Squamish, British Columbia
Natural High has the 2QM15 and she is smoothest at 22-2300. 2500 gets a resonance going that will actually vibrate in the mast if the backstay isn't tight.

Re: Preferred cruising RPM ? [Re: NaturalHigh] #9589
05/27/10 03:43 AM
05/27/10 03:43 AM
Joined: Oct 2007
Posts: 160
Vancouver, BC, Canada
dlabrosse Offline
Senior Member
dlabrosse  Offline
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Joined: Oct 2007
Posts: 160
Vancouver, BC, Canada
Bill, Thanks for the tip about fuel consumption. I had my suspicions that fuel consumption was considerably greater at high rpms but really had no idea it was that significant. This makes alot of sense though and I will have to keep it in mind the next time the wife pushes me to do 6.5 knots to get the next crossing over with.


Dominique Labrosse
Red Five, #92
Re: Preferred cruising RPM ? [Re: dlabrosse] #9590
05/27/10 07:32 AM
05/27/10 07:32 AM
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Rhapsody #348 Offline
Past J/30 Class President
Rhapsody #348  Offline
Past J/30 Class President
Joined: May 2007
Posts: 2,668
Portsmouth, RI
Dominique - there is an older post that has the Yanmar power curves. Look at the slope of engine power at the prop versus RPM. Going from approximately 2400 to 2900 RPM doubles the power output. In fluid flow, (depending on the type of flow and some other factors), power is related to the speed cubed and fuel consumption is linearly related to the power output. Theoretical hull speed on the J/30 is about 6.7 kts. Once you get close to that speed (in calm water), you're really burning fuel fast trying to go any faster.

Re: Preferred cruising RPM ? [Re: Rhapsody #348] #9695
06/18/10 06:09 PM
06/18/10 06:09 PM
Joined: Oct 2009
Posts: 381
Squamish, British Columbia
NaturalHigh Offline
Senior Member
NaturalHigh  Offline
Senior Member
Joined: Oct 2009
Posts: 381
Squamish, British Columbia
On my delivery to Swiftsure I ran Natural High at 2100 RPM which is nice and easy on the ears. She sipped a cool 0.46 gph (US) or 1.75 Lph

Last edited by NaturalHigh; 06/18/10 06:12 PM.
Re: Preferred cruising RPM ? [Re: NaturalHigh] #9705
06/22/10 01:09 AM
06/22/10 01:09 AM
Joined: Apr 2004
Posts: 457
Highland Park, NJ
Steve Buzbee Offline
Senior Member
Steve Buzbee  Offline
Senior Member
Joined: Apr 2004
Posts: 457
Highland Park, NJ
On my last delivery, I tested RPM and speed-2800 RPM added about a half knot to boat speed over 2300 RPM. Fuel consuption at 2800 was right around .5 gallons per hour. A 1/2 knot of speed cuts about an hour off of a 60 mile trip.


Steve Buzbee
Blue Meanie J/30 #485
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