I have a Westerbeke 30B3 in mine, which was built from the Mitsubishi L3E. Fine little engine that I spread all OVER the salon floor last year because I'm stupid and just haaaaaad to look at the piston tops. No matter, fine little fueler that has not let me down yet. I run 'er around 2400 rpm, it just feels right to me. I'm working it, without pushing it. The long answer is I get better than an hour on a gallon. This boat was 'listed' at 9 thou I think, so with all my stuff and upgrades would easily top 'er out above ten thousand pounds. It also has a 14-RH-12 Michigan wheel on it.
For what it is worth, it strikes me as "over" powered as hell, which I LOVE!! Seriously, what a tug. I think I could easily raft up an identical boat and go where I pleased. But really, it uses so little fuel I almost forget about it. 21 gallon tank that I hope I never have to use but about 18 of, and I'll get tired before it does.
Parts are high, (duhh), if you deal with Westerbeke or Moyer. Riiiight. It better be something damn unusual before I go that route, I one time bought a HEAD GASKET from them at 200 bucks. I think I have a better plan in the future..