5 Gallons per hour would be at a specific RPM and load. We on Macgregors typically run at lower RPM and lower loads than other boats because most of us run at ~6 knots (hull speed) so our fuel consumption per hour is relatively low. Assuming no current or wind I would be surprised if you use more than 2 gallons per hour at 6knots and will likely be FAR less than that, probably less than 1 gallon per hour. Let’s assume a worst case scenario of 2 gallons per hour at 6 knots so 12 gallons multiplied by 6 knots = a range of 24 nautical miles. That is probably worst case though and in reality you will probably burn less than 1 gallon per hour and have a range of 50+ nautical miles with 12 gallons. With all of that being said if you run at WOT (wide open throttle, meaning as fast as your motor can go) you could probably burn 5 gallons per hour or more and have a range of between 15 and 20 nautical miles. There are a lot of variables (wind, current, waves etc) and each engine and boat will be different.