A lot depends on how you run the boat, and load you have. Colby's numbers seem a little low, on mpg. There have been several performance reviews such as Boat Test.com. These have also been used for the factory brochures and web sites in the past. However these are optimistic, since it usually a new boat, no bottom paint, no water, two persons aboard, and only partial fuel load. Also most of the fuel flow studies are with 2 stroke 70 or 4 stroke 90 hp.
The current brochure gives up to 250 mile range. That would have to be a light boat, and some displacement speed. Figure that you only probably have 22 to 24 gallons usable in each tank. Then add in a 10% factor for "safety". Assume 4 miles per gallon (may be closer to 3.5?)..Lets say a respectable 4 miles per gallon, and 44 gallons usable. That would give 176 mile range less 10%, or about 160 miles. There have been times on long trips, where I have dropped down to displacement speed where you can get over 5 miles per gallon. That would give you about 200 mile range.
This is why I have had fuel flow meters on my C Dorys. Most will give MPG and amount used. They can be quite accurate when calibrated.
