2.1 Establish the following principal parameters:
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.1 the subdivision length, Ls - Regulation
1(b)
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.2 the subdivision breadth, B1 - Regulation
1(d)(i)
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.3 the subdivision breadth, B2 - Regulation
1(d)(ii)
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.4 the deepest subdivision draught, ds -
Regulation 1(a)(ii)
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.5 the number of main compartments
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.6 the ship's maximum operational KG at the deepest
subdivision draught.
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2.2 For each of the main compartments establish
the following:
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.1 the values of X1, X2 -
Regulation 6(b)
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.2 the corresponding 
values - Regulation 6(b)
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.3 using the values obtained from .1 and .2, calculate:
`a' - see regulation 6(b), formula (III)
`p' - see regulation 6(c), formula (IV)
`r' - see regulation 7(b)(ii), formula (X) (where longitudinal
subdivision is concerned).
2.3 The calculation of the `s' factor is by the
use of the formula given in page 3, annex 5, of SLF 35/20. The formula
is:
When the criteria for compliance with the requirements
of regulation II-1 of the 1974 SOLAS Convention, as amended, are fully
met, then s = 1 is to be assumed. The `s' factor is only to be calculated
for the deepest subdivision draught (ds), rather than for
the three draughts specified for the full resolution A.265(VIII) method.
The deepest subdivision draught in this instance is the subdivision
draught appropriate to the vessel.
2.4 The damage stability results which are used
to obtain the residual characteristics, that is, GZmax,
range and area under the curve, are to be based on the ship's maximum
operational KG at the deepest subdivision draught. Level trim is to
be assumed.
2.5 A tabular summary of `a', `p', `r', `s' should
now be made for all the main compartments. The product a x (pr) x
s is to be calculated for each damage case to obtain the contribution
to the index `A' (say δA > 0). A summation of the `δA`
values is then made to obtain the contribution to the `A` value from
the single compartments alone.
2.6 The procedure outlined above is now performed
for all cases involving the assumed flooding of two adjacent compartments.
2.7 If the vessel is not fully compliant with
the required residual stability standard, then at least one of the
damage cases appropriate to the subdivision standard will have an
`s' value which is less then 1, i.e:
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.1 for a two-compartment vessel, at least on two-compartment
damage case will have s < 1;
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.2 for a one-compartment vessel, at least one
one-compartment damage case will have s < 1.
2.8 After this the KG described in 2.4 above is
to be modified such that the results of the worst damage case just
meet the required residual stability standard, i.e. s = 1 for the
worst case.
2.9 A subdivision index Amax is then
calculated at the same draught and trim used in 2.4 above but using
the modified KG value described in 2.8 above. All single and two-compartment
groups contributing to the index are to be included. For a vessel
having a two-compartment standard, this means that all `s' values
will be equal to 1. For a vessel having a one-compartment standard,
all one-compartment damages will have `s' values equal to 1.