I woul add that engine size has less to do with fuel economy in boats than
it does in cars. You will get better fuel economy with a smaler engine but
not dramatically so for the same speed with the same load. Engines work a
lot harder moving boats than the do cars. Planing boats with gas engines
are not fuel effecient.

"Captain Chaos" wrote in message
...
I'm looking to buy a late 80's 19' runabout with a Chevy 350 motor.
Intend to tow an inflatable, cruise the lake, and occasional fishing.

How much fuel can I expect to consume cruising at 20-25 mph? How less
fuel efficient would this boat be compared to one with a smaller
motor?