Does this sound right to you

[Shrek]

This weekend is the first time that I have done a measured experiment to determine my GPH burn rate. According to my calculations, determined over the course of two runs of 25 miles each way across the lake, I am burning 10 GPH (2.5 mpg) at 3600 rpm at 30 mph with a V-20cc with a carburated 1998 Merc 225 offshore turning a 19p stainless no brand prop. I got this in a relatively mild sea state with the jackplate up as far as it will go(anti-ventilation plate at the surface) and a touch of bow down on the tabs. I add that there were a few starts and stops across the way and a bit of idling time while I was fetching frosted barley pops from the cooler.

Does this sound about right performance wise and is there anything I can do besides dialing the speed back further to increase efficiency It seems close to me, but I figured it would be good for at least another .5 MPH. FWIW, with this same set up, the boat tops out at 51mph at 5700rpm. I'm just looking to gain efficiency any where I can to get to the big snapper offshore.

What say the brain trust

[tsubaki]

Sounds like you might have found the sweet spot for the boat/engines performance. It's hard to tell without a lot of testing unless you have a fuel flow monitor. Slower or faster speed may or may not improve those numbers (obviously).

I've still got to try another prop, and recheck mine, currently running a 19 pitch on a 150 horse.
Some of the numbers.
44mph - 18.5gph - 2.37mpg
37mph - 14.0gph - 2.64mpg
30mph - 11.0gph - 2.7mpg
4mph - 1.18gph - 3.38mpg

[jasoncooperpcola]

a new motor. My 85 Johnson 150 tops out at 5500 rpm and we are only getting 32 mph. And after going out 25 miles and back offshore the 60 gallon belly tank is empty.

[garagenc]

My 91 V20 with 350 I/O Volvo Penta dual prop at 3000 rpm puts me at 30 mph and 3.8 m/g.

[phatdaddy]

94 150 merc carb avg 2.5 mpg