A Treatise On The Principles And Practice Of Dock Engineering

LAND DREDGERS. 79 have a fair chance of displaying its maximum capabilities. On the Manchester Ship Canal, where there was much greater scope, Sir E. Leader Williams records the following as being the best single-day performances on different sections of the work :* — No. 3 section, 1,943 cubic yards; No. 5 section, 1,624 cubic yards; No. 7 section, 2,250 cubic yards; No. 8 section, 2,025 cubic yards. “These,” observes Sir Edward, “are remarkable figures; but the soil and other circumstances must be suitable in order to afford such results. The average day’s work on all the districts was about 1,500 cubic yards. If 440 waggons, containing 1,650 cubic yards, were filled per day on No. 8 section, it was considered a fair day’s work. A bonus of a penny per cubic yard was paid to the men on everything above this quantity. For the excavation of this quantity the average daily expenses of the machine in wages of crew, coal, stores, and repairs, the last item being heavy, were about 60s., or 0'44d. per cubic yard excavated. There were employed upon the excavator an engine-driver and a stoker, and, round it, a number of men, varying from 28 to 43, the average number being 35, the roads requiring frequent moving.” German Machine. —The land dredger, illustrated in figs. 44, 45, and 46, was made by the Lübecker Maschinenbau-Gesellschaft. Similar in principle aud in mode of action to the French machine, it will only be necessary to touch upon the points of difference, which are of but secondary importance. The German excavator has greater stability, owing to its broader base, and its motive power is sufficient to propel it forward at a rate com- mensurate with the speed of filling the waggons; hence, an attendant locomotive is unnecessary. The machine is some 10 tons less in weight than the French machine, and is generally of lighter build, but the initial oost is about the same. The following particulars of its work upon the Manchester Ship Oanal are taken from the paper by Sir E. Leader Williams already referred to :— “ The best day’s performances that are recorded in its favour are as follows :—No. 3 section, 2,073 cubic yards; No. 4 section, 1,736 cubic yards; No. 5 section, 1,725 cubic yards; and No. 6 section, 2,400 cubic yards. The average day’s work is 1,416 cubic yards, with an average number of 36 men. The average daily expenses of the machine in wages of crew, coal, stores, and repairs are about 60s., or 0’5d. per cubic yard excavated, which is increased to l'6d. per cubic yard by the wages of the labourers who attend on the excavator.” “ Summarising the results of experience in the working of land dredgers in England, it may be said that in light material and on level ground they will fill waggons at considerable speed and with economy ; and where large excavations of soft material have to be made with rapidity, the bücket dredging system gives the cheapest and best results. But they * Williams on “ Mechanical Appliances employed in the Construction of the Man- chester Ship Canal,” Min. Proc. I. Mech. E., 1891, p. 418.