Regulation 13-1.1
1 If the transverse watertight bulkheads in a region of the ship are carried to a higher
deck than in the remainder of the ship, openings located in the bulkhead at the step may
be considered as being located above the freeboard deck.
2 All openings in the shell plating below the upper deck throughout that region of the
ship should be treated as being below the freeboard deck, similar to the bulkhead deck
for passenger ships (see relevant figure under regulation 13 above), and the provisions
of regulation 15 should be applied.