"Gould 0738" wrote in message
...
Best economy is at 1000RPM (4.3mph): 10.33mpg

At 1500rpm (5.7mph) : 6.7mpg

At 4000rpm (27.2mph): 7.22mpg

Now that seems more reasonable.
A 2500 rpm increase taking the boat from
6 mph to 27 is more believable (to me) than a 500 rpm increase taking the
boat
from 9mph to 25.

The reason the first one didn't make sense to you is that you're forgetting
that the point of maximum drag is at the speed you're running right before
you jump on plane. At 9 mph, that boat is pushing tons of water. At 25
mph, that boat is displacing much less water.