Albin 28/30 RPM/Speed/Fuel Table

[johnmurray]

Just before my boat was hauled on 9 October I did some measured runs to prepare a table showing average speed at selected RPMS along with an estimate of fuel usage at each RPM level. The results are shown below. 4250 RPMS is wide open throttle (for me) with the Yanmar 315 engine and that delivered an average speed as measured by the GPS of 28.5 miles per hour (about 24.8 knots). It is noteworthy that the fuel usage per mile at that speed appears to be about three times the usage at the most economical speed. I wonder if others have similar findings.

Katie G
RPM/SPEED/FUEL USAGE
RPM SPEED(MPH) EST FUEL (LTR/MILE)
1000 5.4 1.0
1500 7.5 1.1
2000 8.7 1.2
2500 10.5 1.8
3000 15.2 2.0
3500 19.9 2.3
4000 25.7 2.7
4250 28.5 3.0

[craw_daddy]

Thanks for posting your consumption info -I have converted it to some other units that may be of interest (south of the border) ..

RPM/SPEED/FUEL USAGE
RPM-------gal/mile---------MPG------SPEED (KTS)------gal/hr
100----------0.26-----------3.8-----------4.7---------------1.43
1500---------0.29-----------3.4-----------6.5--------------2.18
2000---------0.32-----------3.2-----------7.6--------------2.76
2500---------0.48-----------2.1-----------9.1--------------4.99
3000---------0.53-----------1.9----------13.2--------------8.03
3500---------0.61-----------1.6----------17.3-------------12.09
4000---------0.71-----------1.4----------22.3-------------18.33
4250---------0.79-----------1.3----------24.8-------------22.58

[Mariner]

If someone can convert that info back to gallons per hour, I can put it into my spreadsheet and generate some efficiency curves.

[craw_daddy]

[RobS]

3000 it is....

[fairtide]

I am surprised to find values for the Yanmar 315 hp engine installed in the 28TE with rpm above the maximum listed 3800 per the manufacturer's literature. It was nice to find the lower rpm information that has been a missing part of the picture. Often, how fast a boat can be driven, say in a marina, overshadows how slowly it can move without a trolling valve.
On a somewhat unrelated topic, I have read articles about engine life and the ones that seem to make sense to me state that engine durability is inversely proportional to the amount of fuel that is consumed. Slow operation with little demand on the engine results in longer engine life, it is said. Of course, it is smart to vary the engine speed and to run it hard every so often.
The answer to the question of whether a 3X increase in fuel consumption from slowest speed to quickest seems realistic is yes. It takes lots more energy to move the boat faster. It's the operator's choice, as in driving a car, to opt for economy or performance.

[johnmurray]

I too, was surprised to see my engine run up to 4250 RPMs at WOT. I assume that is accurate, at least to the extent that the RPM counter is accurate. I am not any kind of an engine expert so I rely on an exprienced diesel mechanic for servicing. He seems to think everything is OK. Should I be worrying about something?

[RobS]

I too, was surprised to see my engine run up to 4250 RPMs at WOT. I assume that is accurate, at least to the extent that the RPM counter is accurate. I am not any kind of an engine expert so I rely on an exprienced diesel mechanic for servicing. He seems to think everything is OK. Should I be worrying about something?

I would have the mechanic photo-tach the engine at different rpms and verify the accuracy (or inaccuracy) of your tach. 4250 is a bit on the high side - 4000 fully loaded would be right on. If your tach is on the money you could probably speak to a prop shop about adding some pitch to your prop. If you tell them how many rpm's you are looking to give up they should be able to suggest the required prop work, about an inch of pitch for a 100 rpms is norm. Overpropping is more the concern for engine over-load and damage but I would still look into it further by starting with the photo-tach.