Making it to Seneca Shoal on a 16 gallon tank is more a matter of how efficient your motor is and what your running. I only have a 6 gallon tank for my 30 hp tiller and know I can go all day long on it trolling and make a 10 mile run each way in the process. If you have a gas gauge try to figure out your mpg's. The shoal is about 3.5 miles from the south gap.
As for the fishing we put 8 on the ice Saturday before the wind became to much for me. To bad we only made two passes before we had to pull trigger to head in.