Where approval of a lesser height is requested, justifying information is to be submitted, such as arrangements provided to prevent personnel going over the guard rails or bulwarks. The opening below the lowest course of the guard rails is not to exceed 230 mm (9 in.). The other courses are not to have more than 380 mm (15 in.) clear opening. In the case of units with rounded gunwales, the guard rail supports are to be placed on the flat of the deck.