The cross-pieces, or bilge-cods, are of oak, the four central pairs being 37 feet long and the remaining three, 33 feet long. They are secured to the centre longitudinal by placing the ends of a pair of cods together, and wedging out against two cast-iron knee-pieces with small teeth on their faces, these fit into holes in the cods. The bilge-cods are shaped on the upper face to a slope of about 1 in 14, and for the greater part of their length, strips of iron, 3 inches wide, are let into them and upon these run the sliding bilge-blocks. The longitudinals at the bottom of the cradle are framed into oak cross-pieces, and are stiffened by four cast-iron brackets.

At about every 20 feet in length of the main and auxiliary cradles, a pawl is fixed under the centre beam, working in the rack between the rails. When not in use, it may be lifted up into a horizontal position. The auxiliary cradles have no bilge-cods or blocks. Chains are fixed to the sides of the main cradle and attached to the auxiliary lengths near the centre. They have a sectional area of 1 square inch and are provided with adjusting screws. The rollers are 8 inches in diameter, 3 inches wide on the face, with a flange inch deep. They are of iron, cast round a 1ğ-inch Bessemer steel shaft, bossed out and roughened in the centre. The wrought

iron draw-rods are double and have a minimum sectional area of 16 square 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, placed 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 Iwall 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 consists of oak logs, bolted together, and the lower portion of pitchpine timbers,

* Rudloff on "Docks," Int. Nav. Cong., Dusseldorf, 1902.

secured in the same way. The bilge-blocks, for supporting the bottom of a ship on both sides of the keel, consist of strong pitchpine timbers, arranged scaffold fashion, resting upon cradles, which are drawn under the ship and adjusted by wire ropes, passing through rollers. The cradles move on special slides bordered with iron, and are spaced 27 feet apart.

The graving dock is constructed parallel to and adjoining a large sea-lock, which, generally speaking, was built under the same conditions as the dock. The experience, gained during the former undertaking, proved very useful in carrying out the second without any serious interruption. The work proceeded in the following manner :

Preliminary operations consisted in digging out trenches to a depth of 3 feet 3 inches below zero or about 14 feet 9 inches below ground level, by means of a land dredger, and the excavated material (soft clay) was carried off in tipping waggons and utilised for raising the ground all over the harbour site. In the trenches thus formed, 12-inch sheet piling was driven, averaging 55 feet in depth, to enclose the dock foundation proper. A second row of piles was driven at the same time to serve as anchorage to the sheet piling. When this had been done, water was admitted into the trenches from the harbour, and excavation was continued down to the bottom of the foundation by means of a floating bucket-dredger. But as the latter was incapable of working at a depth of 58 feet, and as grabs did not work satisfactorily, the trenches had to be closed again by dams and pumped out for the concluding portion of this work.

After the trenches had been carried down to the required depth, water was admitted to them a second time, and the bottom layer of concrete, composed of 1 part of lime, 1 of trass, and 1 of sand to 4 parts coarse river gravel from the Weser, deposited in skips. The whole of the foundations were completed in 15 weeks at the rate of 800 cubic yards a day, the maximum output being 930 cubic yards in twenty hours. The average thickness of the foundation was 19 feet 6 inches.

The layer of concrete was left undisturbed for a period of three months, after which it was pumped dry and levelled to an even surface, being further strengthened with strong iron bands, to prevent its breaking up. The building of the walls was then proceeded with. They were mainly constructed in concrete, with a hard clinker facing and granite copings, quoins, and bedstones. No leakage occurred through the concrete foundation, but a strong flow through a gap in the sheet piling was conducted into the pump well without giving further difficulty.

The pumping plant consists of two 49-inch centrifugal pumps for emptying the dock, and two 10-inch centrifugal pumps for dealing with the leakage water. The former set are driven by special, direct-coupled, triple-expansion engines. Each pump can lift on an average 150 cubic feet a second, and as the dock holds 2,700,000 cubic feet, it can be emptied in 2 hours. The drainage pumps are driven by 30 H.P. compound engines. Only one drainage pump is needed, as a rule, and that intermittently.