Engine Efficiency

[markpierce]

My JD4045's (2400 max. RPM) "sweet spot" is 1800 RPM providing 6.3 knots, a knot below hull speed, at less than 2 GPH. That's better than 3 nautical miles per gallon. There is a slight visible vibration of the Coot's propeller shaft between 1900 and 2100 RPM so avoid them. Hull speed is achieved at 2200 RPM using 4 GPH, or less than 2 nautical miles per gallon. That extra knot, a 16 percent increase, increases fuel consumption rate by over 50 percent. With strong adverse currents, however, the difference in fuel consumption for speed over ground/bottom, decreases.

 

[Larry M]

...With strong adverse currents, however, the difference in fuel consumption for speed over ground/bottom, decreases.

Here’s our trip summary for both Colombia to Aruba and Aruba to Curacao. On the Colombia trip we had some positive current and 15 kts on the nose (average). On the Aruba trip we had ~2 knots of contrary current and 25 knots on the nose.

Santa Marta to Aruba 1.46 gph 3.82 mpg 5.6 knot average
Aruba to Curacao 1.74 gph 2.11 mpg 3.6 knot average

 

[Tom.B]

Your Perkins is roughly equivalent to my Lehman

You know, Ben, I would have thought so too, but when we were together coming from Morehead two weeks ago, you were running the same speed and I, but, according to your cool chart (and I want to remember we chatted on the radio about it), were running several hundred rpm's less than us. I suppose it gets down to prop pitch because our hull speed is probably roughly the equal.

I am at 17. Do you know yours?

 

[Ben]

I am at 17. Do you know yours?

My prop is a 21x24

 

[Tom.B]

Well, that explains quite a bit now doesn't it. ;-)

And what's with the new avatar pic?

 

[Codger2]

Well, that explains quite a bit now doesn't it. ;-)

Indeed it does.

 

[Blue Heron]

My prop is a 17/21

 

[Ben]

Well, that explains quite a bit now doesn't it. ;-)

Bigger equipment, longer stroke, smoother motion. Makes sense to me.