18.—(1) All deadlights which are accessible, all watertight doors, all valves and closing mechanisms of scuppers and the devices referred to in regulation 16(4) shall be opened and closed for purposes of drill—
(a)at intervals of not more than seven days; and
(b)immediately before the ship proceeds to sea if the ship is intended to remain at sea for a period of more than seven days.
(2) All closing appliances and devices referred to in regulation 16(1) and (4) shall be inspected by a person appointed by the master for that purpose before the ship proceeds on any voyage.
(3) The following closing appliances and mechanisms are to be inspected at intervals of not more than seven days by a person appointed for that purpose either generally or on any particular occasion by the master—
(a)all valves, the closing of which is necessary to make watertight any compartment below the margin line; and
(b)all valves, the operation of which is necessary for the efficient operation of damage-control cross-connections.