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ieee : MARINE REVIEW. = ¥ : AN IMMENSE COFFERDAM ot REQUIRED TO REPAIR THE LEAK AT THE BIG NEW TIMBER DOCK IN BROOKLYN NAVY YARD--NO WATER NOW ENTERING THE DOCK. The large wooden dry dock at the Brooklyn navy yard, officially known as No. 3, is just now the scene of a costly and difficult engineering work of a kind which has rarely been undertaken before. It will be remem- pered that this structure is the latest and largest wooden dock constructed in this country. It was built to accommodate the large battleships and cruisers which have recently been added to the navy, and it was more than anything else the necessity of having dry dock accommodation at the earliest possible moment which led to the dock being built of wood instead of the more lasting and reliable stone. The length of this dock over all is 670 feet, breadth 151 feet, and the depth on sill 29 feet. The site consisted largely of made ground, and in preparing the designs special care was taken to prevent the seepage of water by providing several complete lines of sheet piling--continuous walls of heavy, square piles, which are tongued and grooved, and driven in close contact-- which completely encircle the dock. There is one of these around the edge of the floor and another 26 feet back from the coping of the dock. They connect at the entrance of the dock with wing walls, of sheet piling, which are driven at right angles to the axis of the dock at each of the two sills and at the outer edge of the apron. The new dock had not been many months in use before a serious leak developed, the water showing itself at the joints of the altar steps, near the caisson gate. It was at first supposed that water was making its way in by way of an old bulkhead which intersected the site of the dock on the north side. By sending a diver down on the outside of the caisson gate, however, and distributing coloring matter near the bed of the entrance channel, it was proved that the water was working its way in at that point, as the discoloration shortly appeared on the inside of the dock. This was rendered yet more probable by the discovery of a large hole which had been washed out just in front of the apron at the point marked A in the accompanying diagram. The broken appearance OF a: Celt YAS4 77 yokes and bolted. The sheet piling is 12 by 14 inches and tongued and grooved. It is driven 16 feet into the mud, and in the four walls there are 1,100 separate sticks 56 feet in length. The sheet piling was carried well into the banks of the channel, the concrete coping of the dock being blasted out for this purpose. The three walls of piling were then braced by a system of 1%-inch tie bolts and 12 by 12-inch braces, the latter being notched onto the guide wales and well spiked, both to the wales and the guide piles. The structure was also braced at each end against the sides of the dock with heavy sticks of timber, S S, and 7-inch iron chains were carried back from the top of the cofferdam to the mooring- posts on the dock, and drawn taut by means of turnbuckles. The cheapest bid that could be obtained for supplying the material for filling the cofferdam was $1.75 per cubic yard, and 80 cents per yard was asked for digging up the clayey soil in the neighborhood of the dock. Finally a lump contract at,40 cents per yard was closed for sup- plying the 18,000 yards required by using the mud excavated for the adjoining Wallabout dock extension. This was brought round in scows and unloaded by dredges at the dam. This mud has answered admirably for the purpose and proved quite impervious to water. The saving in this direction has fairly well offset the costly delays due to the failure of contractors to supply the timber. The dock was emptied by the regular dock pumps, and, as the water fell, the cofferdam proved to be a re- markably tight job, practically no water coming through. It was found, as expected, that the whole line of piling at the point where the leak had been located was more or less battered up and torn away by the dredge bucket. To make the dock thoroughly secure against further trouble, two lines of sheet piling will be driven, one in front of the damaged piling and another at the outer sill. The new piles will be heavier--12 by 12 inch, in place of 8 by 12--and they will be 35 feet in length and driven as deep as they will go in the mud. The new piling will be driven up the slopes at the sides of the entrance, and carried out to a junction with the outside wall of piling which surrounds the entire dock. The present floor of the apron will be ripped up, the 3 or 4 feet of concrete which underlies it taken out and fresh concrete filled in to as great a FLOATING CAISSON CROSS SECTION THROUGH COFFERDAM CONSTRUCTED AT ENTRANCE TO BIG BROOKLYN DRY DOCK. of the sheet piling at the outer edge of the apron suggested that it had been accidentally torn wp by the bucket of the dredge which had been used to cut out the channel from the river to the dock. In order to examine the break and make the needed repairs it was necessary to build a huge cofferdam across the entrance channel and pump out the water. The magnitude of the task may be judged from: the fact that the channel is 156 feet wide and the depth of the water is 34 feet, measured from mean high water mark. This gives a total hydrostatic pressure of 2,885 tons, which had to be withstood by the cofferdam. The construction of the dam is shown in the sectional diagram, for which we are indebted to Naval Constructor Bowles of the Brooklyn navy yard. The dam consists of a central wall of clay puddle contained within three lines of sheet piling, backed up by two embankments of gravelly clay, the toe of the inner embankment being held by a fourth wall of sheet piling as shown. The cofferdam is curved, presenting a convex face toward the river, or, to speak more strictly, it is built with five plane faces, those on the river side corresponding to the chords of a circle of 125 feet radius. This is done to secure an arch effect and cause the pressure of the water to be transferred to the walls of the channel, the latter acting as abutments. The lateral pressure thus set up is supposed to compress the lines of sheet piling and assist in keeping the joints watertight. Ow- ing to the yielding nature of the sides of the channel, however, and the difficulty of driving the piles at the angles with a snug fit, it is a question whether a straight dam would not have been preferable. It would certainly have been cheaper, for it often took as long to fit and drive the angle piles as to drive the whole of one bent between them. Soon after the commencement of operations, Naval Constructor Bowles was placed in absolute charge of the work, with instructions to push through the repairs with all possible speed. Contracts were at onice let for the 600,000 feet of timber required; a temporary electric light plant was installed, and six pile drivers were put to work. Sticks of the size and quality required for the piling are not kept in stock, and) when the contracts were let the 600,000 B. M. was yet standing in the Georgia pine forests. This had to be cut, dressed, hauled t¢ a southern port and brought up to New York. Delays due to the non-deliyery of the timber were frequent, and it was only by unflagging attention that the work has been brought to the present stage. The first oneration was to drive eight lines of 14 by 14-inch guide piles, in pairs. Then the guide wales (horizontal lines of timbers to keep the sheet piles in line) were bolted in place. As three of these lines on each set were under water, they had to be adjusted by divers. This was slow and laborious work. Where the guide piles were out of line, blocking had to be inserted or notches cut in the guide wales and the piles drawn up to the wales by U-shaped depth as can be conveniently excavated. The flooring will then be relaid in two. courses with broken joints, with its outer edge finished off in snug contact with the new line of piling. The fact.that no water is now entering the dock proves that the leak must all have taken place at the damaged apron; and it is safe to say that when the present repairs are completed, Naval Constructor Bowles will place a perfectly sound dock at the service of the navy yard.--Scientific American. Stock of Grain at Lake Ports. The following table, prepared from reports of the Chicago board of trade, shows the stocks of wheat and corn in store in regular elevators at the principal points of accumulation on the lakes. Dec. 25, 1897: Wheat, bushels. Corn, bushels. Chico, some keceel ke 9,764,000 15,132,000 Dislathqo Oe ee ee ee 1,571,000 1,533,000 Milyaukee er te ec oly 138,000 90,000 b Deneie ee es eae 183,000 108,000 listed, eon) Ceili ary 245,000 452,000 Batelloy emer eed hy rt BO ape 2,009,000 2,729,000 18,910,000 20,044,000 As compared with a week ago, the above figures show, at the several points named, an increase of 1,697,000 bushels of wheat and a decrease of 1,408,000 bushels of corn. Grain afloat on the canals aggregates 46,000 bushels (oats). There is a great variety in the types of light-draft boats that are being built in different parts of the country for service on the Yukon river, Alaska. A boat to be built by Lewis Nixon of Elizabeth, N. J., for a Philadelphia company, of which Thomas L..Hill is manager, will have a steel hull, and will be 70 feet long between perpendiculars, 83 feet over all, 15 feet 4 inches beam, and 3 feet 3 inches depth of hold. The vessel will be able to carry about 60 tons on 30 inches draft. Two engines will drive a paddle wheel at the stern. Engines will have cylinders 7 inches in diameter by 28 inches stroke. The boat will be steered by two balanced rudiders. : Subscribers to the Review who have been receiving the paper through the marine postoffice, Detroit, will please notify us of home addresses at once, in order that changes may be made for the winter. All charts sold by the Marine Review are corrected to date of sale.