HELL GATE (ante) IMPROVEMENTS. Hell Gate may be more particularly described as that part of the East river between Long island and Manhattan island, also between Long island and Ward's island, and between Ward's island and Manhattan island. (Lit tle Hell Gate is an unimportant small passage between Ward's island and Randall's, lying to the n. and having a transverse direction). The reefs of rock in the main passage, some of which were islands at low tide, caused with the rising and falling of the tide numerous whirlpools and eddies, which rendered navigation at times really dangerous, always dif ficult; and for large ships impossible, although the depth in the tortuous channel might be sufficient.
A survey was made as long ago as 1848 by (then) lieut.-commanding Charles H. Davis and David Porter, of the S. navy, and in their reports they recommended the destruction by blasting of Pot rock, Frying pan, and Way's reef, which lie between Long island and Ward's island. Lieut. Davis proposed also to clear the middle chan nel, between Long island and Manhattan orNew York island, and immediately below Ward's island, which contains Little Mill rock, Great Mill rock, Middle reef, Heel Tap rock, and others; but lieut. Porter advised rather the destruction of a part of Hallett's point, which, in connection with Ward's island, turns the current in the east channel toward Manhattan island, forcing it against the current of the w. channel at right angles. The destruction of the whole of IIallett's point would allow the two currents to meet at a very small angle, but such an operation, it was thought, would require alto gether a greater outlay than would be practicable, and the advantages would be slight, because the usefulness of both shores of the river requires the removal of the middle obstructions.
The science of submarine blasting as now understood, had no existence at that time. Where the currents in a stream allowed of the operation, diving-bells were often used as a means of drilling and blasting, but the fierce currents of Hell Gate precluded this method. Physics had taught that the inertia of liquids and even gases could be made available as a reacting force, in mechanical operations, if the primary force or impulse were approximately instantaneous; indeed, ordinary mathematical reasoning leads to this conclusion. The idea of using superjacent water as a "tamping" by simply the explosive upon the surface of the rock was first successfully put into prac tice by M. Maillefert, with whom a contract was made to remove obstructions in Hell Gate, the money, $14,000, being raised by citizens of New York. He commenced work in Aug., 1851, by a process which consisted in letting down a can of gunpowder on the surface of the rock and exploding it by means of the galvanic current. The can, as a rule, contained about 125 lbs. of gunpowder. He operated upon Pot rock, Frying pan, Way's reef, Shelldrake, Bald-headed Billy, Hoyt's rocks, Diamond reef, and Hallett's point reef. Upon the latter, however, he produced no sensible effect. He reduced the most prominent surfaces of these rocks to an average depth of about 16 ft. ; some to 18 ft. depth; one, Way's reef, only to 14. These rocks were originally from 5 to 15 ft. below lowwater mark. He fired in all 620 charges, 284 being upon Pot rock. Bald headed Billy was blown into deep water with one charge. Six charges, having an aggre
gate of 750 pounds of powder, and a cost of only $500, deepened Shelldrake from 8 to 16 feet. Other rocks gave more trouble, the deepening of Pot rock from 8 to 18.3 ft. requiring over 34,000 pounds of powder, and costing $6,837.
Congress, in 1851, appropriated to the work $20,000, and of this $18,000 went toward lowering Pot rock to a depth of 20 ft., under the direction of maj. Fraser; the great cost of lowering only two additional feet being in consequence of the considerable increase of surface, and the smoother condition of it. The method was by surface blasting as has been practiced by M. Maillefert. In 1856 it was recommended by the advisory council to the commissioners to further deepen the rocks in Hell Gate, and by the method not of surface blasting, but of drilling. Their statement that this could be easily effected is somewhat remarkable when it is considered that no method of drilling had up to this time been employed, except by use of the diving-bell, impracticable in Hell Gate. Nothing, however, was done until 1866, when brevet maj.gen. John New ton of the U. S. engineers, was ordered to make a survey, the report of which he made to congress in 1867. He proposed the construction of a drilling scow which should be moored at the site of operations. A dome made of boiler iron, of a hemispherical shape, 30 ft. in diameter, served as a framework for 30 drill tubes. This dome rested upon self-adjustable legs, and was let down to the surface of the rock from amidships of the scow. The self-adjustable legs allowed it to settle in a firm and unmovable position, as 'regarded the action of. the The machine was not coin menced till July, 1869, owing to want of funds. It was constructed, and put into opera tiou on Diamond reef, near the mouth of the East river, in May, 1871. Coenties reef was also operated on with this scow in alternation with the work on Diamond reef. These operations proving satisfactory, the machine was taken to Hell Gate, and 17 holes were drilled into Frying pan rock in July, 1872. Also 11 surface blasts were made. In Aug. of the same year the scow was put to work on Pot rock, where it remained until the close of the year. During this time there happened some sixteen collisions with passing vessels, which caused much delay, so that it was deemed proper to surrender the work until more efficient regulation§ could be had in regard to pilots. However, during the five months' work on Pot rock, 40 holes were drilled and blasted, and GO seam blasts and 24 surface blasts were made. The debris had to be removed by divers during slack water. On account of the rapidity of the current at any other time, 'Way's reef, which had been reduced to a depth of 14 ft. in 1857, and again in 1869 to 173 ft. by surface blasting, was attacked by the drilling scow in Aug., 1874, and by the end of Jan., 1875, it was reduced to a depth of 26 ft., at mean low water. This rock was 235 ft. long by a maximum width 115 feet. There were 262 boles drilled, having an aggregate depth of 2,130, or an average of a little more than 8 ft. for each hole. The explosives used were over 15,000 pounds of nitro-glycerine for drill blasts and about 1500 pounds for surface blasts; also, 38 pounds of dynamite.