Physical Description of Titanic
The following description of the vessel is taken from the official British Board of Trade report on the disaster. Most of the details are familiar, but this information is provided for easy reference. For brevity and clarity, only those elements of the ship that are germane to this discussion have been included:
The Steamship "Titanic"
The "Titanic" was a three-screw vessel of 46,328 tons gross and 21,831 net register tons, built by Messrs. Harland and Wolff for the White Star Line service between Southampton and New York. She was registered as a British steamship at the port of Liverpool, her official number being 131,428. Her registered dimensions were:
Length ... ... ... ... ... ... ... 852.5 ft.
Breadth .. ... ... ... ... ... ... 92.5 ft.
Depth from top of keel to top beam at lowest point of sheer of C. Deck, the highest deck which extends continuously from
bow to stern ... ... ... ... ...64 ft. 9 in.
Depth of hold .. ... ... ... ... ... 59-58 ft.
Displacement at 34 ft. 7 in. is .. . 52,310 tons.
Structural Arrangements The structural arrangements of the "Titanic" consisted primarily of:
(1) An outer shell of steel plating, giving form to the ship up to the top decks.
(2) Steel Decks These were enumerated as follows:
C, D, E and F were continuous from end to end of the ship. The decks below were continuous outside the boiler and engine-rooms and extended to the ends of the ship. Except in small patches none of these decks was watertight in the steel parts, except...the Orlop deck aft.
G deck, 190 ft. forward of boilers, 210 ft. aft of machinery
Orlop Deck, 190 ft. forward of boilers, 210 ft. aft of machinery
(3) Transverse Vertical Bulkheads There were 15 transverse watertight bulkheads, by which the ship was divided into 16 separate compartments. These bulkheads are referred to as "A" to "P," commencing forward.
The Orlop deck abaft the turbine engine room and forward of the collision bulkhead was watertight. All the decks had large openings or hatchways in them in each compartment, so that water could rise freely through them.
The watertightness of bulkheads extended up to one or the other of the decks D or E; the bulkhead A extended to C, but was only watertight to D deck. Bulkheads A and B...further extended watertight up to the underside of D deck.
Bulkheads A and B forward, and P aft, had no openings in them. All the other watertight bulkheads had openings in them, which were fitted with watertight doors. Bulkheads D to O, both inclusive, had each a vertical sliding watertight door at the level of the floor of the engine and boiler rooms for the use of the engineers and firemen. On G deck there were no watertight doors in the bulkheads. On both the F and E decks nearly all the bulkheads had watertight doors, mainly for giving communication between the different blocks of passenger accommodation. All the doors, except those in the engine rooms and boiler rooms, were horizontal sliding doors workable by hand both at the door and at the deck above.
There were twelve vertical sliding watertight doors which completed the watertightness of bulkheads D to O inclusive, in the boiler and engine rooms. These were capable of being simultaneously closed from the bridge. The operation of closing was intended to be preceded by the ringing from the bridge of a warning bell.
The vessel was built throughout of steel and had a cellular double bottom of the usual type, with a floor at every frame, its depth at the center line being 63 in., except in way of the reciprocating machinery, where it was 78 in. For about half of the length of the vessel this double bottom extended up the ship's side to a height of 7 ft. above the keel. Forward and aft of the machinery space the protection of the inner bottom extended to a less height above the keel. It was so divided that there were four separate watertight compartments in the breadth of the vessel. Before and abaft the machinery space there was a watertight division at the centre line only, except in the foremost and aftermost tanks. Above the double bottom the vessel was constructed on the usual transverse frame system, reinforced by web frames, which extended to the highest decks.
The transverse strength of the ship was in part dependent on the 15 transverse watertight bulkheads, which were specially stiffened and strengthened to enable them to stand the necessary pressure in the event of accident, and they were connected by double angles to decks, inner bottom, and shell plating.
Watertight Sub-division. In the preparation of the design of this vessel it was arranged that the bulkheads and divisions should be so placed that the ship would remain afloat in the event of any two adjoining compartments being flooded, and that they should be so built and strengthened that the ship would remain afloat under this condition....The lower part of C bulkhead was doubled, and was in the form of a cofferdam. So far as possible the bulkheads were carried up in one plane to their upper sides, but in cases where they had for any reason to be stepped forward or aft, the deck, in way of the step, was made into a watertight flat, thus completing the watertightness of the compartment....By this sub-division there were in all 73 compartments, 29 of these being above the inner bottom.
Watertight doors. The doors (12 in number) immediately above the inner bottom were in the engine and boiler room spaces. They were of Messrs. Harland and Wolff's latest type, working vertically. The doorplate was of cast iron of heavy section, strongly ribbed. It closed by gravity, and was held in the open position by a clutch which could be released by means of a powerful electro-magnet controlled from the captain's bridge....The time required for the doors to close was between 25 and 30 seconds....The watertight doors on E deck were of horizontal pattern, with wrought steel door plates. Those on F deck ...were of similar type, but had cast iron door plates of heavy section, strongly ribbed. Each of the 'tween deck doors, and each of the vertical doors on the tank top level could be operated by the ordinary hand gear from the deck above the top of the watertight bulkhead, and from a position on the next deck above, almost directly above the door.
Authors note: Although an apparently thorough description of the ship, the official Board Of Trade (BOT) report ignores some details of Titanic's construction that had a direct bearing on both the damage received from the collision with the iceberg and the eventual foundering of the vessel. The BOT report gives the impression that Titanic's double bottom was of uniform design. This is far from the case. Forward of bulkhead "D," Titanic did not have the same double bottom that existed beneath the boiler rooms and engine spaces. The tank top in holds #1, #2, and #3 ended well inboard of the actual shell plating (Fig. 4). The margin plates of the tankage extended downward at only a slight outward angle to the perpendicular. The tank top deck was not continued outward to meet the shell plating. In effect, this meant that instead of a double bottom, the forward holds had what amounted to internal ballast tanks somewhat reminiscent of the McIntyre system of ballast tanks that was already obsolete at the time of Titanic's construction. A key feature of Titanic's tankage beneath the forward holds is that the double bottom did not protect against ingress of water from damage to either the turn of the bilge or the side of the vessel.
Aft of bulkhead "D," the design approached a modern cellular double bottom. The margin plates still dropped nearly vertically to meet the horizontal bottom plating of the shell. However, the floor frames were extended outward by brackets which created the turn of the bilge. These brackets were riveted to the margin plate in way of the transverse floor frames. An extension of the tank top deck extended horizontally on top of these brackets to the shell plating (Fig. 5). Although the drawings do not say, presumably the wing tanks thus created at the turn of the bilge were watertight. The construction of Olympic, the lead ship of the class, was photographed just prior to the installation of the bilge brackets, which can be seen scattered along the length of the building floor of the Harland & Wolff yard.
Because the wing tanks continued the tank top to the shell plating above the turn of the bilge, the double bottom aft of bulkhead "D" did provide protection against ingress of water in either the bottom or at the turn of the bilge.
A significant feature of the Olympic-class of ships was a "Firemen's Passage" and a vertical stair tower containing two circular stairways. This combination of stairs and tunnel allowed the ship's "black gang" to move from their quarters on D, E, F, and G decks to the stokeholds, without passing through the passenger accommodations.
...The firemen's passage, giving direct access from their accommodation to the forward boiler room by stairs at the forward end, contained the various pipes and valves connected with the pumping arrangements at the forward end of the ship, and also the steam pipes conveying steam to the windlass gear forward and exhaust steam pipes leading from the winches and other deck machinery. It was made thoroughly watertight throughout its length, and at its after-end was closed by a watertight vertical sliding door of the same character as other doors on the inner bottom. Special arrangements were made for pumping this space out, if necessary....
The design of this combined horizontal and vertical passageway demands closer inspection. Although not obvious in the ship's accommodation plan of the tank top, the firemen's passageway overhangs the underlying ballast tanks at the head end of hold #2. The walls of the tunnel are outboard of the margin plates of the tanks (Fig. 4). Both the tunnel and the stair tower were watertight, although the tower was watertight only to the upper side of G deck. There was one watertight door at the after end of the tunnel in way of bulkhead "D."
Most descriptions of the Firemen's Passage overlook the attached vestibule at the forward end of boiler room #6. This unusual space was in effect a 17th watertight compartment on the tank top level (Fig. 2). It had the dubious distinction of containing the most watertight doors of any compartment: four. The forward end of the vestibule was protected against flooding of the firemen's passage by the automatic watertight door already mentioned in bulkhead "D." There was an identical vertical sliding door at the after end of the vestibule that separated it from boiler room #6. Two manual watertight doors were also located in this tiny compartment. These were conventional hinged doors that led into the two reserve coal bunker spaces in hold #3. These bunker spaces were located to port and starboard of the firemen's passage, hence the need for two doors. A fifth opening in the vestibule was an escape tower that led to the upper side of F deck.
The stair tower at the forward end of the Firemen's Passage had no watertight closure on any deck. Due to an unusual design, this tower originates on the after side of bulkhead "B" on the tank top. On G deck, it is unexpectedly moved to the forward side of bulkhead "B." This was accomplished by a slight jog in that bulkhead. On the night of April 14-15, water rising in the stair tower did not flood Hold #2 as might be expected, but Hold #1 and all of the other spaces in the compartment forward of bulkhead "B."