304 



ENGINEERING. 



the natural forces were adequate only to main- 

 taining this depth, and that a greater depth 

 could be secured only by contracting the tidal 

 prism. To effect this, it was recommended 

 that a dike be built from near Coney Island 

 in a southwesterly direction toward Sandy 

 Hook. Such a dike would close two of the 

 least used channels, but would increase the 

 natural scour of the Main and Swash channels 

 and would presumably deepen them to thirty 

 feet at mean low water. 



The appropriation, however, was specifi- 

 cally for the deepening of Gedney's channel, 



wheels near the deck. The scoop is lowered 

 to the bottom, where it runs on wheels. The 

 steel connecting pipe contains a ball-and-socket 

 joint, and includes also a short length of heavy 

 India-rubber pipe re-enforced with steel bands, 

 in order to prevent breakage when the vessel 

 is rolling or pitching in a seawny. By means 

 of a steam jet connected witli the top of the 

 centrifugal pump, a vacuum is produced within 

 the pump and pipe, under the effects of which 

 vacuum water rises through the pipes until 

 the pump-chamber is completely filled. Then, 

 on starting the pump and opening the outlet 



FIG. 6. BOAT AT WORK DEEPENING CHANNEL IN NEW YORK HARBOR, WITH DRAWINGS OF DREDGES. 



and hydraulic excavators were employed, which 

 worked by means of centrifugal pumps and 

 deepened the channel two feet over a width 

 of 1.000 feet. In 1886 a further appropriation 

 of $750,000 was granted for the general im- 

 provement of the harbor, and as this was in- 

 sufficient for the proposed dike it was decided 

 to continue dredging operations. 



The contract was awarded to the Joseph 

 Edwards Dredging Company. The vessels em- 

 ployed under this system are propellers, fitted 

 with centrifugal pumps and dredging scoops. 

 Each vessel is divided by bulkheads into tanks 

 for the reception of the dredged material. In 

 the bottom of the tanks are valves operated by 



valve hitherto closed, it at once begins to draw 

 up material. At the upper surface of the 

 scoop, a foot above the bottom of the channel, a 

 water-valve is arranged, which may be opened 

 or closed by means of a small rope or lanyard. 

 This is done from the deck of the propeller, 

 and regulates the proportions of water and 

 solid material. The operative can tell by the 

 sound of the pump whether it is receiving too 

 much or too little solid material, and sets the 

 valve accordingly. When at work, the boat 

 steams ahead at a rate not to exceed two miles 

 an hour, dragging the scoops slowly over the 

 bottom. The pumps are driven as fast as pos- 

 sible, as it is found that their efficiency is cu- 



