Section 69

The attained subdivision index A, calculated in accordance with this regulation, shall not be less than the required subdivision index R, calculated in accordance with sub-regulation (2) of regulation 68.

The attained subdivision index A shall be calculated for the ship by the following formula -

where-i represents each compartment or group of compartments under consideration;

Pi accounts for the probability that only the compartment or group of compartments under consideration may be flooded, disregarding any horizontal subdivision;

,i si accounts for the probability of survival after flooding the compartment or group of compartments under consideration, including the effects of any horizontal subdivision.

In calculating A, level trim shall be used.

This summation covers oniy those cases of flooding which contribute to the value of the attained subdivision index A.

The summation indicated by the formula referred to in sub-regulation

shall be taken over the ship's length for all cases of flooding in which a single compartment or 2 or more adjacent compartments are involved.

Wherever wing compartments are fitted, contribution to the summa-tion indicated by the formula shall be taken for all cases of flooding in which wing 592

compartments are involved; and additionally, for all cases of simultaneous flooding of a wing compartment or compartments and the adjacent inboard compartment or compartments, assuming a rectangular penetration which extends to the ship's centreline, but excludes damage to any centreline bulkhead.

The assumed vertical extent of damage is to extend from the base line upwards to any watertight horizontal subdivision above the water-line or higher.

If a lesser extent will give a more severe result, such extent is to be assumed.

If pipes, ducts or tunnels are situated within assumed flooded compart-ments, arrangements are to be made to ensure that progressive flooding cannot thereby extend to compartments other than those assumed flooded. The Director may permit minor progressive flooding if it is demonstrated that its effects can be easily controlled and the safety of the ship is not impaired.

In the flooding calculations carried out according to the regulations, only one breach of the hull need be assumed.

_,,