A little late to get into this conversation but I have a question???
Why is everyone so concerned about how many miles per gallon they get? Or is this just a different way to get the information then hours per gallon?
Now let me explain. When I was running a 30 ft Allura with a 350 inboard I put on over 1400 hours and I could not tell you what my mpg was.
However I could tell you what my burn rate was per hour and almost any speed. I use to log my hours and every fill up. So if I was going port to port my burn rate would be 8 gph. If I was doing fishing cruising or cock tailing my burn rate was 6 gph. So by using the hour meter and the high end of the burn rate I could always tell how much fuel I had left, and there was confirmation at every fill up.
Anyway that is my story and I am sticking to it.