Yanmar Cruising RPMs

[Jim]

Motoring in the ditch this past weekend, I passed a lot of boats and was passed by others in the same range, size, displacement as my Hunter 380. She has a Yanmar 36hp with dual blade prop. I was cruising at 2800 RPM's and post the question to the group, what do you cruise at, and what do you push as a max in reference to RPM's?

 

[Carl Krave]

Cruising RPMs on H380

I have a 1999 Hunter 380 with a 36 HP Yanmar 3JH2-E. I also have the standard 17" prop that came with the boat.I typically cruise at 3000 or 3100 RPMs. My understanding is that this engine can easily cruise all day at 3400 RPMs (assuming your prop is properly sized and your bottom is relatively clean) without any damage. What you sacrifice is fuel economy for the luxury of speed (my knot meter will show about 6.5 at 3100 RPMs). If you're comfortable cruising at 2800 RPMs, keep on doing it. When I'm motoring, I'm usually in a hurry and I'd prefer to be going a bit faster than I would be at 2800 RPMs.One thing I've noticed on this boat is that it makes a big difference if the prop is clean (i.e., free of barnacles). Smooth is fast and efficient.

 

[Paul Akers]

On my 3HM35F

With a max RPM of 3400 on the 3HM, I typically cruise my Legend 37 (1988) at 2500 - 2600 rpm. This keeps me at 6+ kts. Using the 80% rule, I could bump to 2850 RPM, but I feel that it works a bit too hard for my liking. Also, I sense a proportional increase in the amout of fuel used.

 

[Bob Pugh]

On a recent 10 day outing where there was enough wind to sail for two (2) whole hours off of the Southern California coast, we set the RPM at about 2,600-2,800 and got 6.5 knots consistently from our campbell sailer 3 blade prop on our 2000 Hunter 380. The prop makes a huge difference in cutting through choppy seas. Our fuel economy was great at about .6 gallons per hour of operation.

 

[Carl Krave]

3-Blade prop helps

My friend also owns a 1999 H380 and has a Maxprop 3-blade prop. He can also cruise at 6.5 kts. with 2600-2800 RPMs. The 3-blade prop helps with both power and efficiency. I get about .8 gph at 3000-3100 RPMs to get 6.5 kts. on my standard 2-blade fixed prop. However, I'm not ready to shell out the $3,000 it would take to get a 3-blade prop installed.

 

[Bob Talley]

Yanmar Says

that you can safely motor at 3000 to 3100 rpm, and up to 33-3400 rpm for brief periods. this was the reponse I got when asking the same question at the Annapolis Boat Show. In fact, the Yanmar rep stated it was better for the engine to run at 3-3100 than at 26-2800 rpm. I've been running my 376 at 3-3100. She goes about 6.5 knots and does not seem to be laboring hard.

 

[J. Tesoriero]

70% of rated RPM's

According to some advice in a recent article in Practical Sailor (Aug 1, 2003): in flat water, at average displacement loading, an engine speed of about 70% of rated RPM's (see spec's in engine manual) should yield a boat speed in knots of between 1.1 and 1.15 times the square root of the LWL in feet, provided that your prop diameter and pitch are correctly matched to your boat. Good Luck!