IMPROVEMENTS IN DREDGING.

West Coast Times, Issue 2739, 11 January 1878, Page 2

IMPROVEMENTS IN DREDGING.

An excellent paper was read on the important question of dredging and the improvements recently made in connection therewith, at the Eighteenth Session of the Institute of Naval Architects at Glasgow, by W. Simons E^q., a member of that institute. As the Hopper Dredger system has been commented on of late by several New Zealand papers, we quote Mr Simons's remarks in full. He says :—

" The time allowed by this Institution for papers precludes the possibility of entering at length in o the extensive subject of dredging, which besides more particularly comes under the province of the civil engineer, under whose directions and responsibility are generally entrusted the very various submarine excavations throughout the globe. I therefore propose only to deal with the question of improvements in dredge p lant introduced by my firm, and which have borne favorably the test of practice. For the purpose of comparison, it is 3tated in the annual report of the River Tyne Commissioners that of their two large stationary double dredgers, Nos 4 and 6, the former requires ei^'ht Hopper steamers each of 350 tons capacity to attend it ; and that this fleet dredged and removed and deposited 982,119 tons of debris in the year 1870, being an average of 3777 tons daily, and 703,651 tons in the year 1875, being an average of 2706 tons daily, carried twelve miles off to sea. The other dredger requires six Hopper vessels to attend it, two with steam power and four without (being towed by a tug steamer) or ei«ht vessels in all, such removed and deposited 1,186,707 tons of debris in 1870, and 662,298 tons in 1875, being a daily average of 4564 tons and 2547 tons respectively, carried six miles off to sea. The annual expenses of the the first fleet of nine vessels for working and repairs was £18,550 for each year, and for the second fleet of eight vessels, £12,380 in 1870, and £17,496 in 1875. In Dublin Bay also one large stationary double dredger, attended by four Hopper vesßelp, three of which with steam power and one without (being towed), and each having a capacity of 1000 tons, dredges and removes 6 to 7 miles, 3000 to 4000 tons daily. In 1862, when my firm was invited (by the late Clyde Engineer, Mr Duncan) to design and construct the first Hopper steamer, the idea was considered wild and extravagant, viz., to provide expensive and high class screw steamers for the sole purpose of carrying and depositing mud only, and returning empty. We, however, wrought ou!- the idea and constructed two Hopper steamers for the Clyde Trust, each to carry 300 tons to te9t the question. After a short trial it was found the cost of removing and depositing the debris from the Clyde by these i vessels was only one-third of that by the previous system of punts, tugs, em- | banking, &c , and the Clyde Trust then ordered several more Hopper steamers to be constructed, and have now 18, and our firm since tbe above date have built and engiued about 30 Hopper steamers of from 250 to 500 tons capacity. The Clyde Trust have at present four large stationary I dredgers, besides the above 18 Hoppers, collectively of 1070^nominal horse power, and about 7000 tons Hopper capacity, Prom the experience and information we thereby obtained in constructing these vessels, and their success, and with the view of still further obtaining efficiency and economy in dredging, my firm designed and patented a few years ago, the combined Hopper dredger, the chief properties of which are that, intone bottom, and with one crew, are combined, all the properties of the present dredge fleet, consisting of stationary dredgers, punts, barges, tug-steamers, &c. The first of this new type of dredger we constructed was for the Government of Canada, which, after trial on the Clyde, steamed across the Atlantic in 18 days, and, after three months* experience on its working, the Government sent us an order for another of same type, twice the size and capacity. " This vessel is named the St Lawrence, and it steamed out in twenty days, having been retarded by ice on the voyage. We have since built more, altogether seven, and these are all at work at home and abroad, and have Hopper capacity of from 200 to 1000 tons. One named Willunga steamed to Australia in ninety days, Another named Greeaock, at work on the Clyde, leads its own Hopper capacity with 1000 tons of soft clay or mud in three to three-ancl-a-half hours and steams with such seven to eight miles to deep-sea water, where it is at once deposited and, when not detained the vessel returns to its mooring, all within two hours. Fifteen minutes is usually occupied in picking up its mooring buoys, and recommencing dredging. Its crew is fourteen men, including cook and watchman. Its total working expenses for wages, fuel, and stores is £31 per week. It has been working during all the recent severe gales at Gravel Point, on the Clyde, dredging and depositing regularly at a season and time when, it is submitted, ordinary dredge plant would have been disabled. In three weeks of February last it dredged, removed, and deposited twenty loads, the greater part being the hardiest soil on the Clyde, consisting of clay, and boulderstones mixed with hard boulder clay. I respectfully submit, therefore, that two twin screw Hopper Dredgers, similar tor the model now before the institution, each capable of carrying 1500 tons of its own dredging, are perfectly capable of dredging and removing as much as either the Ty^e or Dublin dredge fleet on the old system. I refer to the one consisting of a fleet of eight to nine vessels, and the other of five vessels, each with its captain, crew^

engineer, consumption, wear and tear, insurance, and maintenance, and occupying four times the harbor or river space. These two Hopper dredges will take £1800 in wages per annum, The two Tyne fleets take £4400 each in wages alone per annum. The former only requires fuel, stores, and repairs for two vessels, the latter for eight or nine. On the Mersey dredging is chiefly inside wet docks, where the gates are only opened at tide time. There is one stationary dredger with two Hopper Fteamers, each of 500 tons capacity, remo- ing five and six loads each per week, stean.ing nine miles to the deposit giound. One Hopper dredger named Caledonian is working in the wet docks at Grang< mouth under similar circumstance- ; i* conveys its own dredgings 18 mile-- to sea, lemoving five and six loads a week, or as many loads as the Merhey Hopper steamers, which require a s'ationary dredger to fill them. It is, therefore, submitted that one Hopi ct dredger of 1000 tons capacity will do equal work to a stationary dredger and its two 500-ton Hopper steamer?, the crew of the former being fourteen, and of the latter twenty-six men, showing a reduction of from 30 to 40 per cent in favor of the Hopper dredger system ; and from our experience in the actual working capability of the seven patent Hopper dredgers we have now constructed, we are warranted in stating that many localities and ports at home and abroad can be deepened by this new type of dredger from 30 to 40 per cent cheaper than by the present system, and we feel satisfied that its introduction is a great 6tep in advance over the present system, as was the adoption (now universal) of the Hopper steamer over the square punts, towing, and embanking by manual labor. The Clyde Trust being chiefly indebted to dredging for their princely revenue of over £200,000 a year ought, naturally, to encourage every improvement in that direction which science can produce. They possess a dredging fleet of 22 vessels, manned, when fully at at work, by 174 men, and costing in wages, fuel, and stores £450 per week, or £18,000 per year of 40 weeks. This fleet removes cay 1£ millions of tons per annum of debris from the Clyde, yet I believe and submit that five steam Hopper dredgers, each to carry 1500 tons of its own spoil (like the model before this Institution) will do the same work, each to load in three or four hours, (me load to be removed from Glasgow Harbor, er less distance, or each dredging and removing five loads per •week, or collectvely, tv?enty-five loads, giving 37,500 tons per week, or 1, 500,000 tons per annum of forty weeks. £175 per week would be their collective expenses, or 67000 a yt ar, and their collective crews would i: umber seventy. In place, therefore, of twenty-two vessels daily obstructing the navigation of the Clyde, there would be only five vessels, and in place of atliu arlship rivtr sj ace of from 60 to 100 feet tein^i at pretei.t occupied at work, there would be only 49 feet. This, compared with tin- present Clyde dredging system, costing £-150 per week, or £18,000 per annum, shows a reduction of £11,000 a year, on the cost of wages and stores alone, and if repairs and maintenance are added, the result is, a saving of from £13,000 to £15,000 a year by the adoption on the Clyde of the Hopper dredger system." •

We observe that Mr W. G. Jenkins of Dunedin, has been appointed Agent for New Zealand, for the constructors, Messrs Simons and Co., of Renfrew, and any further information on the subject, together with photographs of the patent dredge, may be obtained on application. The subject is one well worthy of consideration by such as our own Harbor Board, and by any public bodies who may be entrusted with the charge of changing or silting rivers, er bar harbors, where the dredges are said to be of such groat advantage. (For continuation see fourth page.)