(328 SAFETY OF LIFE AT SEA 



(ii) the two compartments adjacent to the " step " in the bulkhead deck 

 are each within the permissible length corresponding to their 

 respective margin lines, and, in addition, their combined length 

 does not exceed twice the permissible length based on the lower 

 margin line. 



(b) (i) A compartment may exceed the permissible length determined by 

 the rules of Regulation 5 of this Chapter provided the combined length of each 

 pair of adjacent compartments to which the compartment in question is 

 common does not exceed either the floodable length or twice the permissible 

 length, whichever is the less. 



(ii) 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. 



(iii) Where the two adjacent compartments have different factors of 

 subdivision, the combined length of the two compartments shall be determined 

 proportionately. 



(c) In ships 330 feet (or 100 metres) in length and upwards, one of the 

 main transverse bulkheads abaft the forepeak shall be fitted at a distance from 

 forward perpendicular which is not greater than the permissible length. 



(d) 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 2 of this Chapter, and measured at right angles to the 

 centre line 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 paragraph (e) of this Regulation. 



(e) A main transverse bulkhead may be stepped provided that it meets 

 one of the following conditions: — 



(i) the combined length of the two compartments, separated by the 

 bulkhead in question, does not exceed either 90 per cent, of the 

 floodable length or twice the permissible length, except that in 

 ships having a factor of subdivision greater than -9, the combined 

 length of the two compartments in question shall not exceed the 

 permissible length; 



(ii) additional subdivision is provided in way of the step to maintain the 

 same measure of safety as that secured by a plane bulkhead; 



(Iii) the compartment over which the step extends does not exceed the 

 permissible length corresponding to a margin line taken 3 inches 

 (or 76 millimetres) below the step. 



Ch. 2 



