As long as you don't push it too hard it should make it on one tank of fuel. Is there no fuel stops along the way?
If you cruise at 25 mph, it will take about 3 hrs and 15 minutes. 31 gallons divided by 3.25 is 9.5, which means you need to do better than 9.5 gallons per hour. Should be no problem for that boat. Maybe bring along a jerry can just to be sure.