On my 1957 Evinrude 35 I figure on about six miles per gallon so two six gallon tanks gets me 72 miles. If it's a longer cruise I bring extra gas in five gallon plastic tanks that I transfer to my pressure tanks. Also, it's a good idea to carry some extra outboard oil. You guys with newer motors, I am sure, get much better mileage.
1958 Vagabond II & 35 HP Evinrude
1955 PlastiCraft 12 Ft. Delux Runabout
1957 Clipper & twin 35 HP Evinrudes
1957 AlumaCraft 14 Ft. FD
Cruising distance from Arrowhead past Long Island Marina to Ft. Loudon dam is 54 miles (one way) if you take the short cut at Thief Neck Island. Fuel and restroom at Long Island Marina. Maybe fuel only available half way between Long Island and Ft. Loudon dam. Occasional sandy shore line to stop and wade as necessary.
If you want to drive to Kingston City Park from Arrowhead (about 45 minutes) you can cruise on the Emory or the Clinch or even do both. Cruise from Kingston on the Clinch 22 miles to Melton Hill Dam, then cruise 18.5 miles back to the mouth of the Emory River and 13 miles up to Harriman and then 13 miles back to the Clinch and then 3.5 miles back to Kingston. Total of 70 miles cruise. No fuel or restrooms. Nice sandbar on the Emory (we ate there last time) for eating and wading as necessary. Good restrooms and picnic tables at Kingston City park. Just a round trip to Harriman only is 32 miles and a round trip to Melton Hill Dam only is 44 miles.
If you want to cruise the entire length of the Tennessee River on Watts Bar lake between Watts Bar Dam and Ft. Loudon Dam from Arrowhead without taking shortcuts it will be about 148 miles round trip.
If you want to drive another 30 minutes above Kingston you can launch on Melton Hill Lake, Ft. Loudon Lake or Tellico Lake. We are blessed with water in this area.