Page:The American Cyclopædia (1879) Volume VI.djvu/177

DOCK 169 FIG 8. Plan of Brooklyn Dry Dock. with 18 in. of hydraulic concrete, this covered with cross timbers of yellow pine 12 in. square, and this again with 3 ft. granite blocks laid in hydraulic cement. A cross section is rep- resented in fig. 4. The walls, composed of heavy granite blocks laid in hydraulic cement, are carrried up vertically from this foundation, and are 108 ft. from outside to outside, being 5 ft. thick at the coping and 39 ft. at the bot- tom or lower step, and varying in thickness FIG. 4 Transverse Section of Brooklyn Dry Dock. between these two points in accordance with the curve, which is irregular and made to cor- respond with the general curve of the side of a ship. The distance between the quoins in which the folding gates revolve is 66 ft., and this is about the average width of the lock chamber, and also of the length of the deck of the caisson or outer gate, which has also a beam of 16 and a depth of 30 ft. Two culverts, e, c, one on either side of the entrance and below the sur- face at low tide, admit water and carry it in a descending course to the bottom of the dock a few feet in front of the inner gates. These culverts have a calibre of 4 ft. 9 in. vertical by 2 ft. 5 in. horizontal. At the points where they enter the dock commence the discharge culverts, which are carried on either side to a point beyond the head, where they unite and empty into a well under the engine house. From this well the water is pumped into a culvert which descends to the river and dis- charges at a point near the entrance of the dock. The pumping engine can empty the dock in 2h. 10m., its capacity when filled by the tide being about 600,000 cubic feet. "When a ship is docked, the filling culverts are closed, as well as the passages from the dock chamber to the drain- ing culverts leading to the pump well, and the water is pumped from the latter ; the ship is then admitted and placed over the keel block in the centre of the dock ; the caisson is next floated to its place, over the recess or groove, and filled with water until it sinks down to the bottom of the masonry fitted to receive its keel ; after which the turning gates are closed by men standing on the bridge, arid working the four hand wheels that move the machinery. The culvert gates in the dock chamber are next drawn and the water is allowed to flow into the draining culvert and well, by which means