The general structure of the _Titanic_ is shown by the midship section, page 83, and the side elevation, page 129. For about 550 feet amidships she contained 8 steel decks, the boat deck, promenade deck, bridge deck, shelter deck, saloon deck, upper deck, middle deck, and lower deck. The highest steel deck that extended continuously throughout the full length of the ship was the shelter deck. For 550 feet amidships the sideplating of the ship was carried up one deck higher to the bridge deck. The moulded or plated depth of the ship to the shelter deck was 64 feet 3 inches and to the bridge deck 73 feet 3 inches. This great depth of over 73 feet, in conjunction with specially heavy steel decks on the bridge and shelter decks, and the doubling of the plating at the bilges, (where the bottom rounds up into the side,) conjoined with the deep and heavy double bottom, served to give the _Titanic_ the necessary strength to resist the bending stresses to which her long hull was subjected, when steaming across the heavy seas of the Atlantic. The doubling of the plating on the bridge and shelter decks served the same purpose as the cellular steel construction which, as mentioned in the previous chapter, was adopted for the upper deck of the _Great Eastern_. [Illustration: Courtesy of the _Scientific American_ OLYMPIC, SISTER TO TITANIC, REACHING NEW YORK ON MAIDEN VOYAGE] The dimensions of the frames and plating of the hull were determined by the builder's long experience in the construction of large vessels. The cellular double bottom, which extended the full width of the ship, was of unusual depth and strength. Throughout the ship, its depth was 5 feet 3 inches; but in the reciprocating engine-room, it was increased to 6 feet 3 inches. The keel consisted of a single thickness of plating, 1½ inches thick, and a heavy, flat bar, 3 inches in thickness and 19½ inches wide. Generally speaking, the shell plates were 6 feet wide, 30 feet long, and 2½ to 3 tons in weight. The largest of these plates was 36 feet long and weighed 4¼ tons. Amidships, the framing, which consisted of channel sections 10 inches in depth, was spaced 3 feet apart. Throughout the boiler-room spaces, additional frames, 2½ feet deep, were fitted 9 feet apart, and in the engine- and turbine-rooms, similar deep frames were fitted on every second frame, 6 feet apart. These heavy web-frames extended up to the middle deck, a few feet above the water-line, and added greatly to the strength and stiffness of the hull.