Best cruise RPM on VolvoPenta MD2040 for fuel economy

[JonasE]

Next summer we leave for an extended cruise including two ocean crossings. One thing that I still havent figured out is our fuel economy. Both the optimal RPM for fuel economy as well as the fuel consumption per hour at the optimal RPM.

During the 3 months we are sailing from Northern Europe to Gran Canaria before our first ocean crossing I will have calculated the fuel consumption. But I would like to get some help in figuring out the optimal cruise RPM without having to keep refilling and testing back and forth since the tank is not fully rectangular (follows the shape of the hull) and I cannot trust the accuracy of the fuel gage on the tank.

VolvoPenta recommends in the owners manual that the best comfort and fuel economy is to avoid running on full throttle (should not be any surprise). Instead they recommend a cruise RPM 300-500 below the full throttle. In the manual the full throttle range for the MD2010-2040 is 3200-3600 RMP and when we have tested our full throttle it was around 3300 RPM. I cannot find any more information in the workshop manual either regarding fuel economy.

If I would use the most conservative values that would give med a cruise RPM of 2700-2800 RPM (3200-500). Usually I cruise around 2200 RPM and consider 2700-2800 a fairly high RMP.

Does anyone else have a VolvoPenta MD2040 and have figured out the best cruise RPM for fuel economy?

 

[RichardS]

I would say that you have nailed it at 2200 RPM.

Richard

 

[MM5AHO]

Not exactly the same engine, but I have MD2030. At 2000 rpm = 1 litre per hour and 5 knots (with clean hull). 2500rpm drinks 1.8 lph at 5.5=6kn. 3000 rpm digs the stern in and drinks 2-2.5 lph and does 6kn. Boats is Rival 32 - long keel heavy for length boat.

 

[yotter]

We also have a fuel tank shaped to the hull contour (and an inaccurate gauge). We have the 29HP VP2030 and are 34 feet and 6 tonnes. We cruise at 2500 rpm (6 knots)and use pretty close to 2 litre an hour. To work out your fuel consumption for a given rpm fill your tank to full, motor at constant chosen rpm for say 10 hours, fill tank again to full and consumption equals litres to fill tank / 10. Forget looking at the gauge. I know my consumption well at 2500 rpm, but unsure about other speeds. After 20 hours we usually take between 35 and 45 litres. 2500 is a good compromise for us, enough to hopefully stop the exhaust elbow fouling up and not enough to dig the stern in and produce black smoke to dirty the hull. I believe that WoT at 3400 is around 7 litres an hour (bit waves and black smoke) and 200 to 2200 is likely to be 1.5 litre per hour. The engine also has a sweet spot at 2500 rpm.
Angus