SUBAQUEOUS ROCK-CUTTER

Gisborne Times, Volume XXVII, Issue 2454, 19 March 1909, Page 6

SUBAQUEOUS ROCK-CUTTER

M THE LOBNITZ PATENT. ’ ' ~ Mr. Goodwill, representing the Palmer Engieering Company, Wellington, is at present in Gisborne, and has supplied the secretary of the Gisborne Harbor Board (Mr. J. Witty) with-some information in reference to the Lobnitz subaqueous , rock-cutting plant, for which his Inn are agents. The rock-cutter, which is the patent of Messrs Lobnitz and -Co., Renfrew,_ Scotland, pulverise.'-sub-aqueous reck into ballast size to enable it b.eing readily- dredged. Mounted upon a single; or-two joined punts, the plant consists -of a heavy chisel of: .steel, usually weighing 1-0 or 15 lons. This “cutter” ik'a round bar of special mild steel, varying in length; a 4-ton cutter,/measuring 20ft, is suitable for 'depth's not exceeding 17ft, whilst a loton cutter is* suitable for' a depth of /50fb. Hoisted on: a derrick or shearlegs, the cutter is allowed to drop, and by its own weight breaks into the surfacs of the rook, pulverising the same. The whole force of the impact is concentrated upon a few square inches, and this enormous pressure is claimed to crush : the hardest rock. The cutter, which is fitted with renewable hardened points in' the form of armor-piercing shells, is allowed .to' fall on the same spot until it has penetrated to.- the'desired depth. It is found advisable to break the rock in layers of about three feet in thickness. The .plant also comprises the necessary powerful steam hoisting winch capable of delivering about 1500 blows .per day of 10 hours, also -a manoeuvring winch for .shifting the position of the barge containing the rcck-euifsr; The . average results in hard rock have given a minimum of two, cubic feet of rock broken to suitable dredging sizes, for every blow. A crew of four men is required. Rock excavation with cutters is declared to be the most sure and least costly per cubic yard, and also more rapid than any other system laiowu.- Tho expense per cubic yard' may be calculated as follows: —A ciugl-o cutter 'machine will break up per day in average rock IQp cubic yards for one ton or coal and the wages cf four men, and the cost of oil, stores, and repairs does not exceed tne expense for fuel and wages. Over S 3 rock-cutters have been supplied since’ 1106, and used in the Manchester chip canal in deepening from 26ft to 2d.*:< the average quantity broken per month was .6403-cubic yards, at a. cest'of 5.9--d per cubic yard. It is stated that the rock-cutter would deal effectively with tho rock in the channel. The estimate for n 10-ton rock-ou+ter. w’*h a length of 34ft, and a complete set of machinery was £2430. Tfco information is being laid before the Beard at its next meoti?ig.