im thinking of building a sub out of a propane tank (500 gallon), it weighs 1069 pounds ( as it sits now before ribs,con tower,tanks whatever) im trying to figure out the bouyancy of a tank this size so i can calculate how much weight i can build on to it before i reach negative bouyancy,does anyone know the formula for figuring this problem? hahahahaha i would hope so!! thanks bill v