TREATIES If one of the two adjacent compartments is situated inside the machinery space, and the second is situated outside the machinery space, and the average permeability of the portion of the ship in which the second is situated differs from that of the machinery space, the combined length of the two compartments shall be adjusted to the mean average permeability of the two portions of the ship in which the compartments are situated. Where the two adjacent compartments have different factors of subdivision, the combined length of the two compartments shall be determined proportionately. (2.) In ships 430 feet (131 metres) in length and upwards, one of the main transverse bulkheads abaft the fore peak shall be fitted at a distance from the forward perpendicular which is not greater than the permissible length. (3.) A main transverse bulkhead may be recessed provided that all parts of the recess lie inboard of vertical surfaces on both sides of the ship, situated at a distance from the shell plating equal to one-fifth the breadth of the ship, as defined in Regulation I (3), and measured at right angles to the centreline at the level of the deepest subdivision loadline. Any part of a recess which lies outside these limits shall be dealt with as a step in accordance with the following paragraph. (4.) A main transverse bulkhead may be stepped provided that- (a) the combined length of the two compartments, separated by the bulkhead in question, does not exceed 90 per cent. of the floodable length, or (b) additional subdivision is provided in way of the step to main- tain the same measure of safety as that secured by a plane bulkhead. (5.) Where a main transverse bulkhead is recessed or stepped, an equivalent plane bulkhead shall be used in determining the subdivision. (6.) If the distance between two adjacent main transverse bulk- heads, or their equivalent plane bulkheads, or the distance between the transverse planes passing through the nearest stepped portions of the bulkheads, is less than 10 feet (3 05 metres) plus 2 per cent. of the length of the ship, only one of these bulkheads shall be regarded as forming part of the subdivision of the ship in accordance with the provisions of Regulation IV. (7.) Where a main transverse watertight compartment contains local subdivision and it can be shown to the satisfaction of the Ad- ministration that, after any assumed side damage extending over a length of 10 feet (3-05 metres) plus 2 per cent. of the length of the ship, the whole volume of the main compartment will not be flooded, a proportionate allowance may be made in the permissible length otherwise required for such compartment. 1198
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