3 For ships with centrecasings, any horizontal
openings for passenger or vehicle access to the other side need not
be closed and made watertight. The calculation of amount of water
on deck should be made as if the centrecasing is watertight provided
the opening is not greater than 5.5 m in width or the sum of all openings
is not greater than 5.5 m in width. If the opening in the centrecasing
is greater than 5.5 m in width then the calculation of amount of water
on deck should be based upon the deck area on both sides of the centrecasing
and with free flow of water between the two sides.