Cargo ports or similar openings may be submerged provided
the safety of the ship is in no way impaired. It is considered that
the fitting of a second door of equivalent strength and watertightness
is an acceptable arrangement. In this case a leakage detection device
should be provided in the compartment between the two doors. Further,
drainage of this compartment to the bilges controlled by an easily
accessible screw down valve, should be arranged. The outer door should
preferably open outwards.