BB-7 Illinois Class Design
Armor Protection
The belt armor extends from four feet below the normal load line to 3.5 feet above it, and extends from amidships between the turrets, and for the distance occupied by the engines and boilers. The maximum thickness of armor at the water line is maintained from the center line of the after barbettes, where the belt begins, to the forward coal bunker bulkhead, tapering to 10-1/2 inches to the center line of forward barbettes, thence to 4 inches in a distance of 30 feet, which thickness is maintained to the bow of the vessel. The triangular armor extends from the slopes of the protective deck to the top of the armor belt at the forward and after ends of the machinery spaces, 12 inches in thickness.
Above the side belt is a casemate 5-1/2 inches thick, worked from the center line of the forward barbette to the center line of the after barbette. The ends of the belt are formed by the diagonal armor,5-1/2 inches thick, worked from the sides of the vessel to the barbette armor. The thickness of the superstructure armor is 5-1/2 inches. The protective deck between armor bulkheads is 2-1/4 inches thick, and at the extremities, on the side slopes, are fitted plates of armor 3 inches thick forward and 4 inches thick aft. The splinter bulkheads between the 6-inch gun stations are each one piece of plate 60 pounds per square foot. The armor in front of the 6 inch guns on the upper deck amidship and main deck forward is 6 inches thick.
The barbettes are 15 inches thick at the front and 10 inches thick at the rear; the 13-inch turrets are 14 inches thick. The forward conning tower is eliptical in shape, and is 10 inches thick, the after conning tower or signal station is 6 feet in diameter and 6 inches thick. An armor tube 7 inches thick is fitted between the base of the conning tower and the protective deck, to afford protection to the voice pipes, electric wires, engine telegraphs, steering gear and engine tell-tales.
Construction
The hull is constructed of mild steel of domestic manufacture with frames spaced 4 feet apart, except when intermediate frames are required, from the stem to frame No. 76; and from this point aft the frames are spaced 3 feet 6 inches apart. The ship is divided into 309 watertight compartments. The double bottom extends from frame No. 22 to frame No. 75, and runs up to the 5th longitudinal from 31 to 66, and to the 4th longitudinal from 22 to 31 and from 66 to 75. A cofferdam 36 inches wide is constructed between the berth and the protective decks on each side of the vessel, extending from the transverse armor bulkheads to the extremities of the vessel.
On the berth deck a cofferdam 36 inches above the deck and 3 feet wide is worked on each side between frames No. 11 and No. 79, except where the torpedo-tubes are fitted. The cofferdams are filled with fire-proofed corn-pith cellulose packed to a density of 6 pounds per cubic foot. All the wood used in the construction of the vessel is fire-proofed, and the use of the wood at all is avoided wherever practicable. The upper deck and the main deck, outside of the superstructure, are the only ones laid with wood, the others being covered with linoleum.
On the main deck is located the 6-inch battery in broadside, fitted within the superstructure in stalls formed by splinter bulkheads; on this deck are also located the crew's W. C. and the showers, ordnance and pay offices, bakery, drying room, junior officers' mess room, pantry, wardroom, junior and warrant officers' W. C. and the armory. It also forms the principal part of the crew's messing and berthing space.
Below the protective deck are the machinery spaces, dynamo room, coal bunkers, holds, chain lockers, trimming tanks, store rooms, magazines, shell rooms, blower rooms, central station for communications, steering gear, engineers' and ordnance workshops, air compressors and ammunition hoists.
For communication between the various parts of the ship there was a complete system of telephones and voice pipes with call bells. The important stations are connected directly, but for general purposes, in order to lessen the number of pipes, a central station is used.
There wre two steam cutters, one 36 feet and one 33 feet long. They have Ward boilers, compound engines and keel condensers. The engines of both cutters are the same size; cylinders 4 inches and 8 inches in diameter by 6 inches stroke.
There were four searchlights, made by the General Electric Company, two mounted on a platform on the mainmast and two on the pilot house abreast the foremast. The projectors are 30 inches in diameter, and hand controlled. All lamps are of the horizontal type with combination hand or automatic feed, and designed for a current of 75 to 90 amperes at about 50 volts. The carbon holders are adjustable, and the life of the carbon is six hours.
The signal apparatus was in two sets, one for each mast, of the usual Ardois type, and consists of four double signal lanterns to each set, with cable connections and keyboard on the forward and after bridges.
For the auxiliary drainage system, manifolds are fitted in convenient locations throughout the machinery space, with suction pipes leading to the double-bottom compartments, trimming tanks, and principal lower compartments of the ship, and to the sea connections as required. Where these pipes drain water from compartments above the inner bottom a small well is fitted projecting 6 inches into the inner bottom and covered by a plate strainer. All manifold valves are worked from the manifolds only. A 5-inch drain connects the forward and the after manifold, with flanges for the pump connections. In the boiler and the engine compartments the suctions are fitted with flanges for a direct connection to the pumps in that compartment, and the crank pits are drained independently of the remainder of the bilge.
The compartments above the protective deck are drained by scuppers or portable pumps. The small store rooms below the protective deck are drained by portable pumps, and the coal bunkers below the protective deck by their own vertical sliding doors. The waste water from the bath and wash rooms is led by pipes to two tanks located in the forward part of the engineer's workshop, and is pumped overboard by an ejector.
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