9.3.1 During intermediate flooding stages a practical
method of calculating the floating position and residual righting
moments is the added weight method where the intact condition is corrected
for the weights of inflowing floodwater and outflowing cargo.
9.3.2 During each stage an assumed amount of added
floodwater and/or cargo outflow should be used. The following method
is recommended:
-
.1 for a loaded tank, an equal loss of liquid
cargo mass and equal inflow of floodwater mass at each stage resulting
in a total loss of liquid cargo at and total inflow of floodwater
to the final damage equilibrium waterline; and
-
.2 for an empty tank, an equal inflow of floodwater
mass at each stage resulting in total inflow of floodwater to the
final damage equilibrium waterline.
9.3.3 Alternative methods may be accepted, for
example:
-
.1 For a loaded tank the loss of liquid cargo
mass and inflow of floodwater mass is based on a linear change of
total tank content density over each intermediate stage from pure
cargo at the intact condition to pure floodwater at the final damage
equilibrium waterline.
-
.2 For an empty tank an increasing depth of water
at each stage based on the difference between the depth of water in
the tank and the depth to the waterline in way of the tank, divided
by the number of remaining stages, resulting in total inflow of floodwater
to the final damage equilibrium waterline.
9.3.4 Noting that calculation of stability in
the final damage condition assumes both the liquid cargo and the buoyancy
of the damaged spaces to be lost, it is therefore considered both
reasonable and consistent to base the residual GZ curve at each intermediate
stage on the intact displacement minus total liquid cargo loss at
each stage.