J/30 Class Association Forums J/30 Forum Cruising Discussions Preferred cruising RPM ?

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_.

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.

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.

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

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.

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.

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 - 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.

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

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.