Hydrostatic balance loading means that the cargo is loaded in all cargo tanks to an ullage that is greater than the freeboard.
Of hydrostatic balance loading is that at the cargo tank bottom ,the hydrostatic pressure of the cargo oil column plus the inert gas pressure in the ullage space remains equal to hydrostatic pressure of the outside water column thereby mitigating the out flow of the oil in case of bottom damage.
Hydrostatic pressure of cargo oil column + IG pressure in the ullage space = Hydrostatic pressure of outside water column.
Actual level to which the cargo can be loaded in any one tank is governed by a formula containing number of factors which includes:–
- Depth of the tank
- Cargo density
- Normal inert gas over pressure in the tank.
Hydrostatic balanced loading provides an equivalent level of protection against oil pollution in the event of collision or stranding as would the same ship having wing or double bottom spaces meeting the 30% coverage requirement.