A Treatise On The Principles And Practice Of Dock Engineering

496 DOCK ENGINEERING. iron draw-rods are double and have a minimum sectional area of 16 squaie inches, a length between centres of 12 feet 6 inches, and a total length of 312 feet 6 inches. There is also a draw-chain, 49 feet long, with the same sectional area. The Kaiser Graving Dock at Bremerhaven.* This dock was built by the State of Bremen, between 1896 and 1899, to accommodate the large new ships of the North German Lloyd, to which Company it has been let. It is entered from the “ Kaiserhafen,” which itself is connected by locks with the estuary of the River Weser. It is illustrated in figs. 492 to 499. The maximum available nett length of the dock, measured at the level of the keel-blocks, is, in round figures, 741 feet. The dock in this case is closed by a floating caisson, plaoed outside and bearing against the square quoins of the pierhead of the entrance. In its normal position, however, the caisson is berthed 13 feet further inwards at grooves provided midway in the entrance, and, when in this position, the nett length of the dock is only 728 feet. There is yet a third sill, with corresponding grooves for the caisson, within the dock and enclosing a length of 545 feet. The side walls of the main entrance have a batter of 1 in 4, and the mean width of the entrance is about 92 feet. The sill of the dock is laid 8 inches below the sill of the entrance lock between the river and the Kaiserhafen, and is 23 feet 6 inches below the local zero. Ordinary high water is 11 feet 9 inches above zero, giving a draught over the sill of 35 feet 3 inches ; on extremely rare occasions, however, the water in the wet dock may fall to 6 feet 6 inches above zero, and the available draught then becomes 30 feet. The width of the dock bottom has been arranged so as to leave a clearance of 6 feet for workmen on each side of the hull of a vessel, 82 feet wide. The central strip upon which the keel-blocks rest has, like these, a fall of 1 in 600, at the side there is a fall of 1 in 450 towards the inlet channels of the pumping station well, which are placed in the western side wall of the dock behind the inner sill. The floor was subsequently raised for a length of 98 feet at its inner end, so that workmen who are engaged in repairing a ship’s screws, can start upon their work without waiting for all the water to be pumped out. The height of the keel-blocks is 3 feet 6 inches, and this also represents the depth of the dock below the sill. The dock is closed by a floating caisson, which only differs from those of ordinary construction in that it carries a 20-ton crane. The dock can be closed in twenty minutes. The keel-blocks are entirely of timber, spaced at 4 feet 6 inches centres, and have a base area of 6 feet by 20 inches. The upper portion consiste of oak logs, bolted together, and the lower portion of pitchpine timbers, * Rudloff on “ Docks,” Int. Nav. Cong., Dusseldorf, 1902.