250 



ENGINEERING. 



of vegetable and street refuse in twenty-four 

 hours. 



A design for a steam tug-boat for canals, 

 which has been proved by trials on the Saar 

 coal-canal to be free from the objections to the 

 use of steam in narrow canals, is the invention 

 of Paul Jacquel, of Natzweiler, in Alsace. 

 Steamboats have proved useless on ordinary 

 canals, because the waves which are generated 

 by the screws or paddles injure the banks, and 

 for the reasons that the boats are liable to in- 

 jury in passing through locks, and that they can 

 not carry sufficient cargo to pay expenses. In 

 Jacquel's system of tug-boats the screw is placed 

 in the body of the boat, and is surrounded by 

 a cylindrical casing which receives almost the 

 entire force of the wash, the water passing out 

 astern in a stream so concentrated in direction 

 that the banks are preserved. The water is 

 fed in through two large channels leading from 

 the sides of the boat. The screw itself in its 

 sheltered position is safe from injury. The 

 boat being a tug, and always drawing the same 

 depth of water, can transport a large train of 

 barges at three or four times the speed obtained 

 from horses. The tug being steered by its own 

 rudder, the use of steering-poles, which are 

 very detrimental to the banks, is avoided. 



The removal of Flood Rock, a large reef in 

 the middle of the swift and narrow channel 

 entering New York Harbor from Long Island 

 Sound, is the most important of the Hell-Gate 

 improvements, executed at the cost of the Gov- 

 ernment, under the plans and directions of 

 General Newton. Flood Rock is a ledge of 

 gneiss of similar composition to Hallet's Point 

 Reef, which was cleared away by undermining 

 it and leveling the remaining portions by a sin- 

 gle explosion, which took place September 24, 

 1876 (see " Annual Cyclopedia " for that year). 

 The work on Flood Rock was begun in 1876, 

 but suspended for lack of appropriations dur- 

 ing the year 1878, with which intermission it 

 has been prosecuted continuously. The summit 

 of the reef was at all times above water, al- 

 though only a small portion was visible. By 

 raising upon it retaining walls and cribs, an 

 area of about a quarter of an acre was built up 

 above high water, which afforded a suitable 

 foundation for the buildings and a hoisting-tow- 

 er at the opening of the shaft. This was sunk 

 from the apex of the ledge to a depth of about 

 75 feet. The rock which was removed at the 

 mouth of the shaft was utilized at first to fill 

 a deep hole along shore, and then dumped 

 between Little and Great Mill Rocks, a space 

 800 feet in length, in order to constitute with 

 them the western jetty which will confine the 

 new channel to be formed by the removal of 

 Flood Rock. 



The plan of the excavation is the same as 

 that pursued in the leveling of Hallet's Point. 

 The net-work of galleries and cross-galleries 

 covers five acres. Piers, only sufficient in size 

 and number to support the roof of rock which 

 remains, will be left when the mining opera- 



tions are over. These piers will then be 

 drilled and filled with a sufficient quantity of 

 explosives, and the whole mine will be fired 

 simultaneously. The equivalent of 100,000 

 pounds of nitro-glycerine will be employed in 

 the explosion, according to the original esti- 

 mate. After dredging away a portion of the 

 debris it is expected that a channel 26 feet 

 deep, at low water, will be obtained. The 

 length of the galleries completed at Flood 

 Rock at the end of the fiscal year was 13,528 

 feet; the quantity of rock removed, 39,608 

 cubic yards. The mining is expected to be 

 completed at the end of the season of 1883. 

 A considerable proportion of the labor of 

 mining is performed by steam machinery, the 

 most approved modern appliances being em- 

 ployed. The four large boilers on the reef 

 can develop 400 horse-power. They furnish 

 steam to five upright air-compressors, which 

 supply air at a pressure cf 55 pounds on a 

 square inch to 30 drilling-machines, as well as 

 to the winding-engine, a ventilating-engine, a 

 shop-engine, two mining-pumps, and other ma- 

 chinery. The length of galleries driven during 

 the fiscal year 1880-'81 was 6,211 lineal feet, 

 and the stone removed amounted to 21,528 cu- 

 bic yards. During the year 9,823 tons of stone 

 were dredged from Hallet's Point, making the 

 total quantity removed since the explosion 81,- 

 907 tons. Over two thirds of the area for- 

 merly occupied by this reef, the required depth 

 of 26 feet has been obtained. In the remain- 

 ing one third there are still places where the 

 depth is not over 19 or 20 feet at low tide. 

 The estimated cost of the remaining works at 

 Hell Gate is $2,250,000. This comprises the 

 completion of the work at Flood Reef, the re- 

 moval of Heel-Tap and the North Brother 

 reefs, and excavations on Frying-Pan Rock. 

 From Buttermilk Channel, between Governor's 

 Island, in the harbor, and the Brooklyn shore, 

 which was obstructed by a large shoal, with a 

 minimum depth of 9 feet at mean low water, 

 about 80,000 cubic yards have been dredged. 



The Madras breakwater, constructed of le- 

 ton blocks of 27 tons' weight, was subjected 

 to the force of a cyclone on the 12th of No- 

 vember ; about 700 feet of each pier was en- 

 tirely destroyed, and the topmost tier of 

 blocks throughout their entire length was 

 carried away. The failure of the Parkes plan 

 of construction, under the action of a storm 

 which was not more than half as violent as the 

 one which struck the same shores in 1872, will 

 probably lead to the entire rebuilding of the 

 harbor-works. The 27-ton blocks were swept 

 away like shells. The only part of the works 

 which can be utilized in the reconstruction is 

 the rubble mounds. The blocks of the Colom- 

 bo breakwater, designed by Sir John Coode, 

 are 50 tons in weight, the piers are half as 

 wide again as those at Madras, and, what is 

 most important, the blocks are set or "bonded 

 each nearly one half its length over the neigh- 

 boring block, and this wall has five joggle 



