Yanmar 3YM30 Cruise RPM

Tugly · Posted: Sat May 12, 2007 9:26 pm Post subject: Yanmar 3YM30 Cruise RPM

Just got our Ranger 21 - Only been out twice. Pleased with the whole setup. Engine seems to like to run about 2500 RPM. What is the maximum RPM can one run for long periods?

thataway · Posted: Sat May 12, 2007 10:57 pm Post subject:

The WOT for that engine is 3600 RPM. Yanmar says you can run it at 3300. I would personally not exceed 3200 RPM. At 85% WOT you are at 3060 RPM, which would be a good top speed. At the 2500 RPM you are still at the peak of the torque curve, and are putting out about 10 hp at the prop. The fuel consumption would be about half a gallon an hour. At 3200 you are putting out about 20 hp at the prop, and 1.25 gallons an hour fuel consumption.

Since the engine is Natural aspiration, you don't have to worry about carbon in the tubo (and some other problems). As long as you keep the temp up to operating specs (and not over) the engine should be happy and last a very long time. I would personally favor the 2500 rpm where you say the engine sounds good....

davehogue555 · Posted: Sun May 13, 2007 3:23 pm Post subject:

2500 is what mine likes also, I get 6 kts on the nose (7 mph according to the GPS) and sips just about 1/2 gallon per hour at that RPM. I believe that's real close to hull speed for our boats.
Dave

thataway · Posted: Sun May 13, 2007 8:22 pm Post subject:

Assuming that the LWL is 20 feet, 1.34 x sq root 20 = 5.9999 knots. Couldn't be closer! You might be slightly more effecient at 5 knots, but who can complain at .5 gallons an hour--or 12 miles a gallon!