When I talk to my power boat friends (yes, I do have a few) they talk about gallons per hour. I talk about gallons per season. I have a 28 year old 15HP Yanmar with a 20 gallon tank. I fill it up in the spring, use it 70-80 hours and then top it off in the Fall. How many miles that works out to be ????. If you are doing coastal crusing on tank will get you where you need to go. Serious off shore stuff you might need a jerry can or two. Helpful??