Inlets, discharges, and scuppers other than deck scuppers
12.—(1) In every vessel of 12 metres in length and over to which these Rules apply each discharge pipe leading through the hull from spaces below the freeboard deck or from within an enclosed superstructure or deckhouse on the freeboard deck shall have an automatic non-return valve and a positive means of closure from an accessible position except that the requirements of this paragraph shall not apply in those cases where the piping of the scupper or discharge pipe is of substantial thickness and where the entry of water into the vessel through the opening is not likely to lead to dangerous flooding.
(2) In manned machinery spaces in every such vessel controls for main and auxiliary machinery, sea inlets and discharges shall be readily accessible and be provided with indicators showing whether the valves are open or closed. In unmanned machinery spaces suitable warning devices shall be installed to indicate leakage of water into the space or leakage from any other system.
(3) In every such vessel valves and other fittings attached to the hull shall be of steel, bronze or other ductile material and pipes between the hull opening and the valve shall be of steel except that in positions elsewhere and in vessels constructed of materials other than steel, other materials may be used provided that they are suitable for their intended service.