What year and what model? No matter what, you'll probably get 3 - 3.5 MPG unless you run her wide open all the time, or just at/under planing speed. In that case you'll get 2 MPG . . . She might . . . might get 4 MPG at her most efficient cruise speed if you keep her very lightly loaded. They are usually most efficient between 3000 and 3500 RPM. This is a boat thing only, the engine gets better efficiency at other points, but plug her into a boat with one gear, and that's where they work best . . .350 Mercruiser V8 5.7L?
I had a bayliner with a 125 outboard for my last boat. My current boat has a '95, 5.7l with a four barrel carb. The two use about the same as far as gas per day.
Abso-damn-lutely!! And if you really stress about it, and buy based on fuel efficiency instead of power and fun etc., you can save 10% . . . and in the above example that amounts to . . . Drum roll please . . . $5 or $6I have a 50+ gal tank in my 20' w/ 5.7L. We do alot of water sports, with usually 3-4 adults and 3-4 small kids in the boat (so pretty heavily loaded). In a 5-6 hour outting I will easily go through $50-60 in fuel @ $3/gal, easily.
Like others have said, if you are worried about the cost of fuel, either look for a smaller engine or reconsider boating as a hobby (not trying to be a smart-arse). But the way I look at it, what kind of a price do you put on good memories and fun with your family and friends.
Doug
Let's not forget that fuel is practically free when compared to everything else you spend on the boat, mooring charges, insurance, and ugghhh. . . maintenance.