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32 MARINE REVIEW AND MARINE RECORD. : \ *SUCTION DREDGERS--ROTARY CUTTERS. By James Henry Apjohn. The development of hydraulic dredgers has placed in the hends of engineers a tool of enormous power, and the great re- sults achieved by them on the bars of the Mersey and other rivers are well known. They have hitherto been chiefly employed on sand or light silt, which yields to the current drawn into the nozzle by the action of the pumps. To enable a suction-dredger to deal with clay, it is necessary that the clay be first cut up, as the cur- rent is insufficient to disintegrate it. For dredging clay, rotary cutters fitted to the nozzle of the suction-pipes have been used. These consist of a number ot knives (ten to fifteen), united by suitable discs or rings at one or both ends. The knives may be either straight or spiral, and are mounted around, and concen- tric with, the end of the suction-pipe. The whole cutter may, be secured to the end of the suction pipe, and rotary motion 1m- parted to both together, or the cutter shaft may be journaled in a suitable bearing provided in the end of the suction pipe, which 1s then made stationary. : The author's experience of rotary cutters has been with a dredger designed for the purpose of excavating clay for dock ex- tension. The clay being silty, it was thought that it would be easily broken up by the cutter, but this was not the case. 'The cutter had fourteen straight knives, set at an angle of 26° to the tangent of the circle round which they were placed, and over- lapping each other to a slight extent. The dredger was first operated at a small depth, where the soil was loamy, and the cut- ter proved efficient; but when the clay was reached at a greater depth, the openings between the blades of the cutter clogged with the tenacious plastic clay, with the result that the proportion of clay found in the water discharged through the pipe line was -extremely small. The cutter was then unshipped, and a width of some inches was cut off the inner edge of each blade; so that the overlap was done away with, and at the same time the circular opening at the bottom of the cutter was reduced in area. When again tried the cutter worked better, there being but little clog- ging between the blades, but these did not cut the clay very well. A new cutter was then built,with narrow spiral knives, and proved to be more efficient than the first; but even with this cutter the quantity turned out per hour was never more than 60 per cent. of that contracted for. The clay, which it discharged behind the walls, was in the form of nodules, varying in size between that of an egg and that of a Dutch cheese. The form of the discharged clay shows that it is clay, and not, as has been asserted, silt easily disintegrated by water. If it had been the latter, it would, after passing through the pump and line of pipes, have been discharged i the form-of mud, and not as hard balls, as was actually the case. The dredger worked radially, pivoting on one of two "spuds" abreast of each other in the stern, the bow being swung by breast- lines. Having completed the arc, the other spud was dropped and the one in use was raised, so that the dredger advanced step by step against the breast she was cutting. The depth cut on each are was about 2 ft., and the bottom was left practically quite level --very different from that left by a bucket-dredger. This dredger, where the material dredged is discharged directly as backing for the walls.and for the raising of low land behind them, is consid- erably more economical than a bucket-dredger, where the material has first to be discharged into barges, from which it is again car- ried and placed on the land. The efficiency of a cutter evidently depends on the form of the blades, the angle at which they are set, and whether they are straight or spiral, and on the openings be- tween them and at the bottom. To determine absolutely the best form for each description of clay to be cut would involve numer- ous and costly experiments which have not as yet been made. The dredger was tried experimentally in the river to see what she could do on sand. Ina depth of about to ft. of water, and discharging back into the river through about 300 ft. of floating pipe-line, she excavated 113,825 cu. ft. of sand in 514 hours, or at the rate of 21,500 cu. ft. an hour. The quantity excavated in the bed of the river was determined by soundings before and after the dredging operations. She was afterwards used for land re- clamation, dredging sand from the river bed and discharging it on to the bank, through 600 ft. to 900 ft. of pipe, with a lift of 17 ft. on an average. Under these circumstances she discharged 6,500 cu. ft. an hour, or 16%4 per cent. in excess of the contract quan- tity for clay. She was subsequently tried on improving a bar in the river, which had shoaled. The bar was about 800 ft. in width, *Paper read at Engineering Conference, Institute of Civil Engineers, London, cht. IA NEW METAL CARGO HOISTERS. Wrought Iron Hook and Strap, Galvanized Iron Shells and Sheaves. Sheaves fitted with Genu- ine Star Metaline Bush- ings with Metaline Side Bearings. © Star Metaline Bushing. SELF-OILING. These Blocks Save the Rop: and Outwear all others, Send for 1902 Catalogue M. A. R. FREE. Manufactured only by BOSTON & LOCKPORT BLOCK CO., BOSTON, MASS. " - LOCKPORT, N. Y. [isstlesicteisstassshnssssssissiiunncnnsresinistemsieneeenitensnssall [July 2; and the dredger was run three times across it on the same line, discharging to one side back into the river, through the floating pipe-line. She was only worked during such times as there was sufficient current in the river, on either the flood or ebb tide, to carry the dredgings to some distance. The operations extended over 2% days, and resulted in an improvement of the crossing by about 214 ft. for the width required for vessels. As the dredger was only run on one line, the width to which the crossing was improved shows that the cut made by the dredger had the effect of causing the current to continue what the dredger shad com- menced. During these operations on the bar the "spuds were not used, the dredger working on head and stern lines. The tendency of the cutter to cant her out of line was counteracted by a steam hopper barge lashed on one bow. ae The effect on the cutters of working in sand was to wear the ' blades to a considerable extent, but the bearings kept in good order, the sand being excluded from them by an arrangement by which they are lubricated by water under pressure. For work- ing in sand, water-jets for breaking down the material to be dredged are preferred by the engineers on the Mississippi to rotary cutters. Interesting particulars of the dredging of this river will be found in "Notes on the Engineering-Works of the Mississippi River," by Mr. E. F. Dawson, associate member of the Institution of Civil Engineers, executive engineer, public works department, Bombay presidency, published in Calcutta by Mr. Thacker Spink in 1900.. Mr. Dawson was deputed by the government of India to visit and report on the improvements on the Mississippi. At first water-jets, nine or ten in number, 2%4 in, to 3 in. in diameter, with a pressure of 14 lbs. per square inch, were used, but subsequently much better results were obtained by jets 114 in. in diameter, six in number, with a pressure of 65 Ibs. per square inch. HEAVY PLATE PLANER AT CHARLESTOWN YARD. The accompanying illustration shows a_ 32-ft. heavy plate planer built by Messrs. Hilles & Jones of Wilmington, Del., and recently installed in the United States navy yard at Charlestown, Mass. Direct connected to the main driving screw of the planer, Akers, GP, & fF. A., Cleveland, O. through gearing and magnetic clutches, is a 50-H. P. Westing- house multipolar motor of 220 volts and running at slow speed, which furnishes ample power to enable the machine to plane 2-in. armor plate, taking a heavy chip. A thorough test proved the machine to be a powerful tool in every respect. The saddle of the planer is designed to carry two tools, one cutting in each direc- tion, also a third tool for vertical feed, the saddle and tool holder being shifted automatically at any point desired. Mystic Shriners Imperial Council at Saratoga, N. Y., July 7-10, excursion rate, one fare for the round trip by way of the Nickel Plate road. Tickets on sale July 5 and 6, good to return July 20. Full particulars at nearest ticket office, or address E. A. 102, July 2. Sand Sucker for Sale. For Sale--Sand sucker of about 175 tons capacity. Equipped with 8-inch pump. In first-class condition, ready for business. Price right. Louhoff Bros , 35 Chene St., Detroit, Mich. July 23 'Seaboard Steel Castings" A Guarantee of Quality. Open Hearth Steel Castings of the Highest Grade for Locomotive, General Machinery and Shipbuild- ing Work. Subject to U. S. Government, Lloyds, Railroad and Other Highest Bena : Ae oe Seaboard Steel Casting Co., Chester, Pa.