I think I found it, anything that displaces water is buoyant by the factor it displaces, minus the weight of the container. 1 cubic foot of air is 1728 cu.in. There is 231 cu. in. in a gallon. equals 7.48 gallons per cubic foot. Water weights 8.35 lbs per gallon.
7.48x8.35=62.45 is the weight of a cubic of water. If the container holding the water weights 5 pounds, the buoyancy of the container should be neutrally buoyant at 57.45lbs., (same as water)
So, long story short. A gallon of air should float a weight less then 8.35lbs. not including the weight of the container holding the air.
It's not the weight of your boat, but the amount of space it will
displace under the water.
This is my take, please post if I'm off.
Thanks for looking, be safe. schick