Fuel burn question.

[erebus]

Might be of no help whatsoever but, my 18SF with a 1998 Merc 115 has so far burned 20 gallons (half tank), which includes:
A roundtrip run from Meetinghouse pond in Orleans to Chatham Light in Pleasant Bay.
A roundtrip run from Sesuit harbor in Dennis to Billingsgate Shoal and trolling for 3 hrs
And tubing on Long Pond for about an hour.
Had to fill up the oil tank once so far, but she's still burning up that first tank of gas.

Sorry for the fairly vague parameters...