Fuel consumption figures - how accurate?

[rob1699]

Anyone have any idea how accurate are the fuel consumption figures in MBY boat test reports are?

To be specific, I’ve got 2 old test reports from MBY on both the Phantom 40 and 46. The following figures have been given (for cruising speeds):-

P40

RPM SPEED GPH
2,200 21.1 17.1
2,400 23.2 21.5
2,600 25.9 27.7
2,800 28.2 35.5

P46

RPM SPEED GPH
2,000 20.2 17.5
2,200 23.5 22.9
2,400 26.6 30
2,600 29.5 38.4

Considering the 46 is a good deal bigger and heavier than the 40, and has bigger engines too, I’m amazed at the figures being so similar which got me wondering if they are right.

Thoughts appreciated!

Rob

 

[RogerRat]

I agree, the figures on the P40 are reasonable but the P46. seems too close, especially at close to 30 knots.

At full chat the P40 is not supposed to rev that high anyway. As this is an old report, what engines are in these boats?

If you work back to the MPG, in the mid speed range they all seem to use about a one gallon. Can be better than one on the 40' and higher than one on the 46'. At just too slower speed for planing and full throttle, they all seem to waste it.

On a 25 Nm trip you'll use the same fuel at 20-22 knots as 24-26 but just get there quicker. (No, not exactly, but closer than you think!)

You don't really need a mag report to tell you that the P46 will use more fuel though but I see what you mean. I'm fairly sure these tests were done by different people with far too many variables to consider it valuable data.

 

[volvopaul]

Rob I can tell you th 46 does 0.75 at a 24 knot cruise an only gets slightly better at 20 knots thats with tamd74p 480, no doubt you will be a D9 man, that could actually be worse??