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Updated: Nov. 20th, 2007

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From an original newsreel film / Robert Hahn collection
Laying of a Keel Plate - The aftermost part of the 3" x 19 " keel bar, located at the transition point where the keel “kicks up” and connects to the stern frame. From an original newsreel film / Robert Hahn collection
The Engineer / Author's collection
Tank Top of Olympic Looking Aft - Olympic’s Tank Top is in the foreground; work proceeds on Titanic on the adjacent slip. The Engineer / Author’s collection

   Introduction - Titanic was constructed with a “double bottom” in which the lowest part of the hull was formed not by a single layer of steel plating, but by a heavily reinforced structure with the vertical keel as its backbone. With the outer bottom plating forming the “skin” of the ship, the inner bottom plating formed the “Tank Top,” so named because the resultant structure, together with its longitudinal girders and transverse members, formed a series of tanks. These tanks were used to carry water for ballast and boiler feed. In addition to the carriage of water, the double bottom added to the safety of the ship . . . (continued)


Keel Plate and Double Bottom -  A detail from the midship section showing Titanic's keel and floor design.  Illustration by Bruce Beveridge based on original H&W Midship Section

  Keel - Titanic’s keel was laid on March 31, 1909, in Slip No. 3 of Harland & Wolff’s Queen’s Island Shipyard at Belfast. Titanic’s keel was of the “flat-plate” design, formed by a single thickness of plating 30/20 inches thick and reducing to 24/20 inches toward the ends. The keel plate was 52 inches wide at its broadest point and was strengthened below by a flat slab bar 19 inches wide by 3 inches thick. The purpose of this flat slab bar, called a “rubbing strip,” was to protect the flat-plate keel from being damaged if the vessel should run aground. It also protected the keel plate during drydocking.

  In riveted hull construction a flat-plate keel resembled an ordinary strake of outside shell plating, the difference being that it was of much greater thickness than the adjacent strakes. This was necessary not only because of the wear and tear to which this plate was often subjected, but also because, in conjunction with the vertical center keel plate, or “vertical keel,” which stood upon it and to which it was attached, it was a considerable factor in the longitudinal strength of the hull
. . .  (continued)


Image above, Keel Plate and Double Bottom - A detail from the midship section showing Titanic’s keel and floor design.
Illustration, Bruce Beveridge based on original H&W Midship Section.


   Titanic’s Cellular double bottom - The term “cellular” was derived from the fact that the double-bottom space was divided into rectangular cells by the floors and longitudinals. These members acted as deep web frames that resisted and distributed the upward push of the water on the ship’s bottom.

  Titanic’s cellular double bottom, inclusive of the wing tanks, extended out to the ship’s sides with floors on every frame. Because the height of the double bottom corresponded to the vertical keel, it was also 63 inches deep at the centerline, increasing to 75 inches in the Reciprocating Engine Room, taking up the space between the keel and the Tank Top. The double bottom was divided transversely into four longitudinal sections by fitting a longitudinal margin plate approximately 30 feet outboard of either side of the watertight vertical keel amidships
. . . (continued)


Other topics in this chapter: Floors - Inner bottom plating

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Copyright 2007 Beveridge, Hall, Andrews, Klistorner and Braunschweiger.

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