"A vessel is considered to be safe, even in the event of serious damage, if she is able to keep afloat with two adjoining compartments in free communication with the sea. The vessel must therefore have efficient transverse watertight bulkheads so spaced that when any two adjoining compartments are open to the sea, the uppermost deck to which all the bulkheads extend is not brought nearer to the surface of the water than a certain prescribed margin.
"The watertight deck referred to is called the bulkhead deck. The line past which the vessel may not sink is called the margin of safety line.
"The margin of safety line, as defined in the above report, is a line drawn round the side at a distance amidships of three-one-hundredths of the depth at side at that place below the bulkhead deck, and gradually approaching it toward the aft end, where it may be three-two-hundredths of the same depth below it."
By referring to the diagrams on page [66] showing the disposition of bulkheads on certain notable ships, it will be seen that, in the case of the Titanic, the application of the Board of Trade rule called for the extension of the bulkheads amidships only to the upper deck, which, at the loaded draft of 34 feet, was only 10 feet above the water-line! Compare this with the safe construction adopted by Brunel and Scott Russell over fifty-four years ago, who, in constructing the Great Eastern, extended all the bulkheads (see page [83]) to the topmost deck, fully 30 feet above the water-line.
Closing, from the Bridge, All Watertight Doors Throughout the Ship by Pulling a Lever
Before leaving the question of bulkheads, the writer would enter a strong protest against the present practice of placing watertight doors in the main bulkheads below the water-line. They are put there generally for the convenience of the engine- and boiler-room forces, whose duties render it necessary for them to pass from compartment to compartment. As at present constructed, these doors are of the sliding type, and they can be closed simultaneously from the bridge, or separately, by hand. The safer plan is to permit no bulkhead doors below the water-line, and provide in their place elevators or ladders, enclosed in watertight trunks. Access from compartment to compartment must then be had by way of the bulkhead deck.
The advantage of lofty bulkheads was admirably illustrated in the case of the City of Paris and the City of New York, designed by Mr. Biles in 1888. Although these were small ships compared with the Titanic, their fourteen bulkheads were carried one deck higher. Biles laid down the rule that no doors were to be cut through the bulkheads, and in spite of strenuous objections on the grounds of passenger accommodation and general convenience in the operation of the ship, he carried his point.
