HELL-GATE, IMPROVEMENTS AT. 



471 



ter object by a system of floats and iron cur- 

 tains so arranged as to constitute a dam pro- 

 tecting a space of 160 feet long and 40 feet 

 wide, within which the work could go on un- 

 interrupted. Another machine was alterna- 

 tively suggested, embodying the same princi- 

 ple, to consist of an iron caisson or cylinder, 

 pointed at the ends, open at the top and bot- 

 tom, and having self-adjustable legs to accom- 

 modate themselves to the irregularities of the 

 rock, and to support it and keep it level. The 

 top of this structure was to be above the level 

 of the highest tide, and to be framed over so 

 as to form a platform, on which the machinery 

 could be placed, and from which the opera- 

 tions could be conducted. It was important 

 to have it adaptable to all the rocks on which 

 it was intended to operate, whatever their 

 size and shape, and that it be perfectly stable 

 against the action of the currents without be- 

 ing unwieldy. It was furthermore considered 

 necessary to furnish it with a protection 

 against collisions, which 

 were sure to occur from 

 the fleets of vessels pass- 

 ing daily. These con- 

 ditions were fulfilled in 

 the steam drilling cupo- 

 la-scow. The scow is 

 built very heavy and 

 strong; an overhanging 



shortening the moving chains with capstans. 

 When all is fixed, the dome is lowered close to 

 the bottom, and established by letting the legs 

 go to adjust themselves on the bottom. The 

 chains that connect it with the scow are un- 

 slung, and flexible connections are made be- 

 tween the tops of the drill-rods and the piston- 

 rods of the driving-engines. These connections 

 must be flexible, because the dome is fixed on 

 the bottom, while the scow holding the drill- 

 engines is certain to swing for short distances 

 back and forth. When the drill-holes are ready 

 to be charged, the dome is lifted, and the scow, 

 carrying the suspended dome, is swung off to 

 a safe distance, without casting loose the moor- 

 ings. The charges of explosives, in tin cases 

 of different lengths to suit the varying depths 

 of the drill-holes, were carried to the spot upon 

 a small scow, whence the diver descended to 

 insert them into the holes. The leading wires 

 were connected with a battery, and the explo- 

 sion was made with invariably certain effects. 

 Removal of Small Reefe. Operations with the 

 steam drilling scow were completed January, 

 1880, upon Diamond Reef. The rock was cov- 

 ered with a large accumulation of loose mate- 



SCOW SECTIONAL ELEVATION. 



guard, faced with iron, surrounding it as a 

 protection against collisions; and has a well- 

 hole 32 feet in diameter. The caisson or 

 dome is a hemisphere 30 feet in diameter, 

 of a strong iron frame covered with boiler- 

 iron. It is open at the bottom and top, 

 and provided with self-adjustable legs so ar- 

 ranged as to be all let go together after it 

 :s lowered. This caisson or dome is simply 

 a framework affording a fixed support to 21 

 tubes, through which the drills operate. It 

 is connected with the scow by four chains, 

 communicating with four hoisting-engines, by 

 which it is lowered or raised. The scow, hav- 

 ing the dome swung by chains, is anchored 

 over the rock to be operated upon. The diver 

 then goes down to examine the bottom and see 

 that the position is favorable. The position 

 of the scow is changed by lengthening and 



rial which had first to be removed with a dredg- 

 ing-machine, after which all of the ledge that 

 was uncovered was attacked. The holes were 

 drilled from 7 to 13 feet deep, 4 inches in di- 

 ameter at the top, and 3 inches at the bottom, 

 and were charged with from 30 to 55 pounds 

 each of nitro - glycerin. Coenties Reef was 

 worked upon in alternation with Diamond Reef 

 in 1871 and completed in 1875. In 1872 work 

 was begun on Frying-Pan, and there is now 

 22 feet at low water. Work was prosecuted 

 on Pot Rock from Aug. 5 till Dec. 28, 1872, 

 during which period there were 16 collisions. 

 The depth on this rock is now 24 feet. 



Way's Reef, over which the original depth 

 of water was 5 feet, having already been cleared 

 by the application of M. Maillefert's process 

 of surface-blasting in 1851, and again in 1869. 

 to 17 feet, was operated upon from Aug. 4, 



