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1903. ] . MARINE REVIEW AND MARINE RECORD. 21 described _or is of an experimental nature, or in cases of emer- gency. For general purposes this kind of a contract has. been found to be the least satisfactory and the most expensive. The work performed by a dredging plant under this kind of a contract is usually only about 75 per cent. as efficient as when payment is made under either of the other methods. This must be expected, for the reason that the power will not be applied to the point where breakages and expensive delays are liable to result. 'The methods and machinery used by the successful contrac- tor im performing the actual work of excavation would: make ser- vice on such work a good school for the young engineer. The improvement in these methods and machinery during the past twenty-five years has kept pace with improvements along all other lines where machinery has been made to do man's work. This improvement has resulted in work being performed at less than half of the former cost although the price paid for labor and materials is fully a third higher now than then. In this pa- per it is intended only to describe the methods and machinery now in use. At the mouth of the Detroit river it is usually necessary to drill and blast the material before it may be excavated. The drill boats in use are from 60 to 8o ft. long and from 25 to 30 ft. wide, and are held in position by four spuds one at each corner. They are equipped with two or more Ingersoll steam churn drills sup- ported on vertical frames having trucks to permit of the drills being moved horizontally along the edge of the boat. The drills are raised and lowered during the operation of drilling by hy- draulic lifts. The boiler furnishes the steam for operating the drills, the pumps used in connection with the hydraulic lifts, the forge, the electric light plant, and other machinery with which the ordinary drill boat is equipped. The drill boat usually serves the purpose of a machine shop where repairs are made to the entire dredging plant. It is always conveniently near to all parts of the work, and ordinary repairs are quickly made, the contrac- tor usually providing a great variety of tools and machinery for - use in cases of emergency. It is mainly in details of this kind where the profits or losses to the contractor are made. -- OPERATION OF DRILL BOATS AND DREDGES. -The drill boats are usually operated day and night. The holes (about 214 in. in diameter) are made at the corners of 5-ft. squares to a depth of about 3 ft. below the required depth at the rate of about 5 ft. per hour per drill. The amount of explosive used is about one pound of 60 per cent. dynamite per linear foot _of drilling. The holes are charged by inserting the sticks of dynamite with the exploder and battery wires attached into. the bottom of a long pipe, the battery wires leading out through a slit in the side of the pipe. This pipe is lowered .into the drilled hole, the dynamite shoved down with a long ram rod, and the pipe withdrawn, a wire spring clamped to the dynamite stick pre- venting its coming out of the hole. The wires are then attached to the battery and the dynamite exploded. During this operation the drill boat is not moved, nor does the work of operating the other drills cease except at the time of firing. On two occasions, however, the charge of dynamite came out of the hole and was exploded directly underneath the boat, causing it to sink almost immediately. This may be attributed to carelessness, however, as before exploding the dynamite the battery wires should be' drawn. up until taut, indicating that it is in place. A quantity of dynamite is always kept conveniently near the work, but no more than one day's supply is kept at the drill boat and this 1s stored in a small scow tailing off the down-stream end of the boat at a safe distance. : x _ The dredges used in excavating the material are of the type known as the dipper dredge. They vary in length from 80 to 135 ft. and in width from 30 to 40 ft., and are held in position by three spuds (from 34 to 36 in. square), two at the bow and one at the stern. The machinery for operating dredges varies greatly, the best recently-constructed dredges being equipped with _ machinery for raising the dredge on the forward spuds (known as pinning up) instead of by swinging the dipper as formerly. The dredge is moved forward in the cut by means of the dipper arm, and the width of the cut is usually from 15 to 20 ft. The capacity of the dredge dipper varies from 2 to 5 cu. yds. for rock work, and from 4 to 7 cu. yds. for earth work. The amount of material removed by one dredge per hour varies from 20 to 100 cu. yds. in rock, and from 75 to 125 cu. yds. in earth. The best type of dredges, however, in soft material and under favorable conditions are capable of removing from 250 to 300 cu. yds. per hour. The time delayed for repairs usually varies from one-fifth to one-third of the time actually worked. A United States inspector is sta- tioned on each dredge to see that the work is being performed in accordance with 'the specifications, and to keep such record as may be required showing the progress made in the prosecution of the work. esnh ths : After the entire width of the area to be improved has been worked over by the dredge, cut by cut, the derrick scow follows after to remove 'such loose pieces of rock as may have been left projecting above the required depth. The derrick scows are one ually from 80 to 100 ft, long and from 20 to 25 ft. wide and they are equipped with an ordinary hoisting engine and derrick vo ble of lifting from 12 to 18 tons, and a complete diving outfit. When lifting the boulders, the derrick scow is pinned up and "4 ported on two spuds, each about 1 ft. square. The -- to be removed is found by means of an iron bar, about 30 it. i "suspended from the side of the scow to the required ---- \ny obstruction str ai by this bar as the scow 1s swept over the im- proved area is removed by the derrick by means of a chain, which is placed in position by a diver. ___ After the area has been thus improved and cleared of obstruc- tions an examination is made on the part of the United States to determine if the required depth has been secured. This examina- tion consists in sweeping the entire area with bars suspended to the required depth. These bars (about 20 ft. long) are suspended by chains from a raft (100 ft. long and 20 ft. wide) built of squared timbers, the raft being held in position by a rope leading to a head anchor and pulled back and forth by means of ropes leading to side anchors. Any obstruction found during this ex- amination is removed by the derrick scow with diving outfit. During the progress of the work, as well as during this final ex- amination, constant attention is paid to the water gauge in order to allow for the fluctuations in the water surface. Following this examination and on the completion of the work required un- der the contract, the final survey is made, which survey consists in the taking of soundings at regular intervals as described above. On this final survey and on the original survey depend the esti- mate for final payment. The cost per month of operating a dredging plant such as is used on the Detroit river is about as follows: Drill boat operated 24 hours per day by double crews .... ..$3,000 Dredge operated 12 holire per day... ee 2,500 Derrick scow operated 10 hours per day ................. 1,500 Tug operated 12 hours per day ....... CE a ea ee 750 Pole $8 10 SND wee Te a ara $7,750 FLUCTUATION OF WATER SURFACE AT THE LIME-KILNS. In this paper, reference has been made to the fluctuation of the water surface at the mouth of the Detroit river, and as this fluctuation at times seriously affects the interests of navigation it is worthy of further consideration. Prior to 1896, tri-daily water gauge readings were taken from a staff gauge nailed to the dock only during the season of active operations (from May to November) ; from 1896 to 1899 these readings were continued dur- ing the entire year; in May, 1899, a self-registering water gauge was installed and since that time the record has been complete. The change in the elevation of the water surface is at a maximum during the late fall months, and this change is due to the direction and force of wind and inequalities of barometric pressure. The maximum daily fluctuation since May 1899 was 5.8 ft. caused by the gale of Sept..12, 1900, the length of time elapsing between the highest and lowest stages being 9 hours. The extreme fluc- -tuation since May 1899, was 7.55 ft., the highest stage being 574.45 ft. above mean tide at New York on Sept. 24, 1902, and on Sept. . 7, 1903, and the lowest stage being 567.30 on Nov. 21, 1900. Daily fluctuations of from 1 to 2 ft, are not infrequent, causing vessels to be detained on account of low water at Lime-Kiln crossing. To give some' idea of the extent of this detention the following information has been compiled: ' Depth at crossing Hours less than duration. September and October ........ IQOI T7185 tt 212 INGYCMDED 6s a IQOI 17:0 Tt. I4I September and October .......: 1902 180 ft. 86 November is2...5,.5 oo. ae ae 1902 17.5 {t, 59 . September and October ........ 1903 18.0 fee November 2, 72, 0 1903 17.516 104 The longest continued period of low water was 58 hours on Nov. 17-19, 1903. At no other place along the channels connecting the great lakes is the change.in the water surface so great nor its effect on navigation so serious. In order to make a through channel of 21 ft. depth available at the mouth of the Detroit river during the entire navigation season (except during the period of storms), it will be necessary to deepen this channel about 2 ft. below the erie heretofore adopted. This deepening will soon be under- taken. With the increase in the number and size of vessels, the block- ing of a channel of 600 ft. width may at any time be expected as the result of collision or other accident. It is now therefore ap- parent that to insure a safe channel to the commerce which may be expected within the next ten years, the present channel will have to be widened oz a second channel excavated. Without en- tering at too great length into this question, it now appears that ~ a second channel would be desirable and also that this second channel should be to the west of Grosse isle making an all-Ameri- can route. j ~ Mr. A.-Hackett, keeper of the Bois Blanc island light and | who also has the care of other aids to navigation near the mouth of the Detroit river, rightfully says that the sinking of the 'steamer Gladstone in 'collision at Bar point recently should not in any way be attributed to the condition of channel marks in that vicinity at the time. The buoys, whch are maintained by the Canadian government, were then in position and when they were _ removed at a later date they were replaced by winter buoys. "The steamer Petrel," says Mr. Hackett, "only brought in the gas buoy from Bar point when it was in danger of being carried away by ice and not until some days after the Gladstone had been raised and taken to Detroit. I would also say that all the float lights of the Lime-Kiln crossing and the Amherstburg channel were kept in position until carried away and lost by ice." a