1.1 At the thirty-fifth session of the SLF Sub-Committee,
following a proposal by the United States (SLF 35/4/23), it was agreed
that a simplified version of resolution A.265(VIII) should be used
to assess the survivability characteristics of existing ro-ro passenger
ferries (SLF 35/20, paragraphs 4.21, 4.27 to 4.32 and annex 5 refers).
1.2 The method proposed involves a calculation
procedure which contains all the essential probabilistic elements
of the full resolution A.265(VIII) method given in the “Regulations
on subdivision and stability of passenger ships as an equivalent to
Part B of chapter II of the International Convention for the Safety
of Life at Sea, 1960".
1.3 The principal probabilistic elements mentioned
in 1.2 are the factors `a', `p', `r' and `s'.
-
`a' is a fact or which estimates the probability
of damage occurring at a particular position in the ship's length;
-
`p' is a factor which estimates the probability
of the longitudinal extent of damage;
-
`r' is a factor which estimates the probability
of the degree of penetration in from the ship side (this factor is
only relevant where longitudinal subdivision is taken into account);
and
-
`s' is a factor which is a measure of survival
probability. When s = 0, this means that there is no contribution
to the index `A' for the damage case being considered. When s = 1,
this means that all the conditions for survival given by the specified
residual stability criteria are fully met.
1.4 The factors `a' and `p', which refer to the
centre of damage and longitudinal extent of damage, are to be taken
directly from formulae (III) and (IV) or regulations 6(b) and 6(c)
respectively.
1.5 Where longitudinal subdivision is provided,
allowance can be given for this - and it should be noted at this point
that such subdivision may be inboard or outboard of the B/5 line.
In such cases, the `r' factor given at formula (X) of regulation 7(b)(ii)
is to be used. However, the deterministic requirement of a minimum
double bottom height of B/10 of regulation 7(a)(i) is not to be applied.
1.6 In the case of the `s' factor, however, the
formula for `s' is to be that which was first proposed by the USSR
in SLF 35/4/9, and is reproduced in page 3, annex 5, of SLF 35/20.
The use of this formula ensures that in all cases where all the SOLAS
90 criteria are met, the `s' factor is equal to 1.
1.7 Further simplification has been introduced
by specifying that the draught calculation of `s' is to be confined
to the deepest subdivision draught, rather than the three draughts
d1, d2 and d3 and corresponding s1,
s2and s3 values given in regulation 6(d)(ii)
of the full resolution A.265(VIII) method.
1.8 Finally, to limit as far as possible the number
of damage stability calculations which need to be carried out and
also to standardize the calculation procedure, regulation 6(a)(ii),
should be applied only as far as the words “... the summation
is also taken for all possible pairs of adjacent compartments." The
remaining wording of regulation 6(b)(ii) should be ignored for the
purpose of this simplified method.