16.—(1) The following closing appliances are to be securely closed before the ship proceeds on any voyage and are to be kept so closed until the ship has been secured at a berth or anchorage—
(a)sidescuttles which can be opened and which are situated below the bulkhead deck;
(b)deadlights of any sidescuttles which are situated below the bulkhead deck and which—
(i)will not be accessible whilst the ship is at sea; or
(ii)are situated in spaces appropriated for use sometimes for the carriage of cargo and sometimes for use by passengers, while such spaces are being used for the carriage of cargo; and
(c)gangway and cargo-loading doors below the bulkhead deck.
(2) No closing appliance described in paragraph (1) shall be considered as being securely closed unless it is locked.
(3) Every portable plate closing an opening below the bulkhead deck in any portion of the internal structure of the ship which is required to be watertight shall be fitted in place before the ship proceeds on any voyage and shall be kept in place, except in case of urgent necessity, until the ship has been secured at a berth or anchorage. In replacing any such plate all reasonable precautions shall be taken to ensure that the joints are watertight.
(4) Both the watertight cover and the automatic non-return valve of any overboard discharge having its inboard opening below the margin line shall be kept closed and secured when such device is not in use.