A Treatise On The Principles And Practice Of Dock Engineering

DISTRIBUTION OF PRESSURE ON KEEL-BLOCKS. 485 Timber Slides, of smooth granite, in the side walls are handy for the purpose of lowering sliores and other timber, but their use is not universal, as in many cases the logs and planks required are thrown into the water while pumping is still proceeding. A Rudder Pit is a useful feature in the event of the removal of a ship’s rudder, though many graving docks are without them, and they are only required on rare occasions. There are two such pits at the Canada Graving Dock, Liverpool, each 50 feet long, 6 feet wide, and 16 feet 6 inches below floor level. When they are not in use for this particular purpose, the keel-blocks are continued over them, being supported on stout girders. A Travelling Crane of large power and wide range, for lifting heavy machinery in and out of a vessel, is essential. A propeller may have to be lifted from the dock bottom or even from the ship’s hold, and in the latter case it would have to clear the hatchway coaming and the bulwark, both of which will in most cases be above the coping level. A lifting power of not less than 25 tons and up to 50 tons should be provided, with a clear outreach beyond the centre line of dock floor, and a height of 30 feet from coping level to under side of jib. The great amount of outreach is more particularly requisite in the case of vessels with twin screw propellers. In addition to hydraulic mains for gate machinery and cranes, it is an advantage to utilise the pipe trenches for the conveyance of electric or pneumatic power to drilling machines, which are very commonly needed to remove plates from the hulls of ships. Portable electric lights are extremely serviceable beneath a ship’s hull. Distribution of Pressure on Keel-blocks. The distribution of the pressure of a ship’s keel over the blocks in a graving dock is a very difficult and complex problem, and one to which no satisfactory solution has yet been propounded, despite the attention which it has received from many eminent scientists and technical experts. Yet the question cannot be ignored, for it has been the cause of several accidents of a very serious nature. A recent disaster which has attracted widespread notice and caused much misgiving, if not dismay, is that which occurred to the North German Lloyd s.s. “Fulda” while in No. 2 Graving Dock, Birken- head, on 2nd February, 1899. Not more than 15 or 20 minutes elapsed, from the time she was left dry upon the blocks till she crashed through them to the dock floor and received such injuries as to become a total loss, constructively. The data involved are these : —The “ Fulda” was a vessel 430 feet in length between perpendiculars, 45 feet 9 inches in breadtb, moulded, and 36 feet 6 inches in depth, moulded. Her displacement, as laden at the time of the accident, was about 6,600 tons; she had a bar keel 12 inches deep and 34 inches wide; the blocks upon which she was docked were of cast iron, with 6-inch greenheart caps and 3 inches soft wood on top of the greenheart (figs. 476 to 479)'. These blocks were 2 feet 6 inches high and