Twelve fathoms
Sand needed: 8*6*1.5 = 72 cubic feet
Two atmospheres is 67.8 feet of water.
78 feet
22.44 gallons for each inch of the water's depth.
72 feet is already linear as feet is linear so answer is 72
Twelve fathoms
At 300 feet of water depth the pressure is about 130 psi
The 260 feet of water: at that depth, there is the weight of the water and the atmosphere on top of it.
About 130 psi at 300 feet of water depth.
660 feet is the water proof depth.
1,000atm is about 33,900 feet of water depth.
It is 2250 cubic feet.
4 atmospheres is about 135.6 feet of water depth.
Sand needed: 8*6*1.5 = 72 cubic feet
72 square feet of course !
5,000 feet of water depth is about 147.5 atmospheres.
72 cubic feet