2 For assessing the effect of the volume of the assumed accumulated seawater on the damaged ro-ro deck in paragraph 1, the following provisions shall prevail:

• .1 a transverse or longitudinal bulkhead shall be considered intact if all parts of it lie inboard of vertical surfaces on both sides of the ship, which are situated at a distance from the shell plating equal to one fifth of the breadth of the ship, as defined in regulation 2, and measured at right angles to the centreline at the level of the deepest subdivision load line;

• .2 in cases where the ship's hull is structurally partly widened for compliance with the provisions of this regulation, the resulting increase of the value of one fifth of the breadth of it is to be used throughout, but shall not govern the location of existing bulkhead penetrations, piping systems, etc., which were acceptable prior to the widening;

• .3 the tightness of transverse or longitudinal bulkheads which are taken into account as effective to confine the assumed accumulated seawater in the compartment concerned on the damaged so-so deck shall be commensurate with the drainage system, and shall withstand hydrostatic pressure in accordance with the results of the damage calculation. Such bulkheads shall be at least 4 m in height;

• .4 for special arrangements like hanging decks and wide side casings, other bulkhead heights may be accepted based on detailed model tests;

• .5 in calculating the effect of the water on the damaged ro-ro deck, the volume and surface effect of the water shall be reduced by 10% to account for the permeability of the ro-ro space;

• .6 the effect of the volume of the assumed accumulated seawater need not be taken into account for any compartment on the damaged ro-ro deck, provided that such a compartment has on each side of the deck freeing ports evenly distributed along the sides of the compartment complying with the following:

  • .6.1
    
    where:

    A	=	is the total area of freeing ports on each side of the deck in square metres; and
    l	=	is the length of the compartment in metres;

  • .6.2 the ship shall maintain the residual freeboard of at least 1 m in the worst damage condition without taking into account the effect of the assumed volume of water on the damaged ro-ro deck;

  • .6.3 such freeing ports shall be located within the height of 0.6 m above the damaged ro-ro deck, and the lower edge of the ports shall be within 2 cm above the damaged ro-ro deck; and

  • .6.4 such freeing ports shall be fitted with closing devices or flaps to prevent water entering the ro-ro deck whilst allowing water, which may accumulate on the ro-ro deck, to drain; and

• .7 when a bulkhead above the ro-ro deck is assumed damaged, both compartments bordering the bulkhead shall be assumed to be flooded but the distribution density of seawater in such compartment may be determined by the following formula:

  
  where:

  d 0	=	is the distribution density when assuming the bulkhead is undamaged, as determined, in accordance with paragraph 1 of these requirements;
  A 1	=	is the area of the larger compartment in square metres; and
  A 2	=	is the area of the smaller compartment in square metres.