I think that 1/2 gallon/ hour would be a safe and conservative budget unless you are really pushing the engine.
Of course you will find out shortly! Fill your tank and keep track of your miles and hours till your next fill-up...then simply divide by the number of gallons you take on. It is useful to have both numbers...and on the ICW since everything is done in mile markers...it is useful to know how many miles you get per gallon.
Bring plenty of extra fuel filters and know how to use them!! Good luck with the trip!
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