A Treatise On The Principles And Practice Of Dock Engineering

DOCK ENGINEERING. 5o6 are built up above the deck level to a triangular profile so as to form three altar courses. The side walls are each 435 feet long and 53 feet 3 inches high, and, in order to give sufficient space for the boilers, they are sponsoned out, forming an upper chamber, 12 feet 6 inches wide. There are four large openings in the walls for the purpose of affording light and ventilation under the bottom of a docked vessel. The three pontoons are subdivided into 40 pumping compartments, and of these 32 are watertight. There are also eight watertight compartments in each side wall. All these divisions are provided with a separate pipe and valve, the pipes leading directly into the two main side drains. The drains are continuous throughout the length of the walls, and as the four 18-inch centrifugal pumps are seated directly on them, any one pump can empty all the compartments of its half of the dock. There is a central bulkhead, dividing tlie dock into two halves, but this is not quite watertight, small leakage holes being purposely left. If, therefore, the whole of the pumping machinery on one side were to break down, the other half could still empty the dock, though at a somewhat slow rate. The pumps are driven each by a separate compound condensing engine directly attached. A return- tube boiler supplies each pair of pumping engines with steam ; but the connections are so made that the supply of steam from any boiler is interchangeable. The working of the whole dock is done from two central positions on the top of the dock towers, where the valve wheels and connections are placed, with indicators to show the condition of the valves, whether open or shut. There are six capstans for warping ships into position, with the usual bollards, fairleads, etc. Lighting at night is done by electricity with 12 arc lamps, beside smaller services. Two 5-ton travelling jib cranes are worked by the same motive power from separate generating plants placed in the dock towers, the leads being mutually interchangeable. The underside of the dock is protected by a series of greenheart keels, as it is possible the dock may ground at low water, and the bottom of the harbour at Bermuda is of coral. The top decks are planked with teak. Figs. 512 to 515 are views of the dock in its various positions.