1The following contrivances shall be securely closed so as to be watertight before the steamer proceeds to sea, and shall always be kept closed while the steamer is at sea, that is to say:—
(a)hinged watertight doors below the margin line, which are fitted in main transverse bulkheads dividing cargo between deck spaces;
(b)sidescuttles in any between deck space, wherein the sill of any sidescuttle which can be opened is below a line drawn on the side of the steamer parallel to the bulkhead deck and having its lowest point four and a half feet, in addition to two and a half per centum of the breadth of the steamer, above the water at the time when the steamer proceeds to sea;
(c)sidescuttles below the margin line which will not be accessible while the steamer is at sea, together with their dead-lights;
(d)gangway, cargo and coaling ports below the margin line.
Provided that in fair weather in tropical waters sub-paragraph (b) of this paragraph shall have effect as if " three and a half feet " were substituted for " four and a half feet. "
For the purpose of this paragraph, a contrivance shall be deemed to be below the margin line if the sill thereof is below that line, and a sidescuttle mentioned in sub-paragraph (b) of this paragraph shall not be deemed to be closed unless it is locked.