Where & what weather, Andy?
Andy, my wife & I surely do envy your location right now. We launced in Urbanna when we first began cruising the Bay and got to help it celebrate its 300th birthday as an incorporated city, a pretty amazing event for most of America!There's really no way to answer your question - in real terms - without knowing more. I assume you're headed down the weather and around the corner, N or S on the Bay, and ultimately to another river...but of course, powering into lots of chop will significantly change your gas per mile figure. That may be why others are hesitant to offer a guess.I'd guess your Johnson fuel burn isn't much different from our Yamaha 8 hp engine which, when we run it on the dinghy near but not at full rpm, is about 3 gals/hr. But how that translates into miles over the ground I can't say. Perhaps the winds will allow you an enjoyable sail and the gas you'll burn will be near the docks. Good luck & good sailing!Jack