Slow in the group so I figured I'd waste some bandwidth. Checked the
mileage and my boat with an 18hp two stroke only makes 2-3 mpg. I figure
it is mostly because I usually go sailing with my son so WOT for 7-10
miles to get where the winds are to his liking and same drill coming
back after the winds die.

Just my guesstimate but we seem to make ~5 knots at 1/3 throttle and ~6
knots at WOT. My GPS went down for the count so I have to get a new one
before I can get good data.

Is this about right for a hull that is in sore need of a bottom
cleaning? I saw some info that seemed to say engine displacement is more
critical then other factors. Specifally I would be much better off with
a smaller perhap four stroke of ~5 hp if I motor like this? I mean it
seems like the 18 hp is mostly overkill and just makes 13 hp worth of
bubbles.

Rick