DRIFTING WITH THE DREDGE. 



733 



the rope was coiled continuously along the whole row. When 

 the dredge was going down, the rope was taken rapidly by the 

 men from these pins in succession, beginning from the one 

 nearest the dredging derrick, and in hauling up a relay of men 

 carried the rope from the drum of the donkey-engine and laid 

 it in coils on the pins, in reverse order. The length of the 

 dredge rope was 3,000 fathoms, nearly three and a half miles. 

 Of this, 2,000 fathoms were hawser-laid, of the best Russian 

 hemp, 2 J inches in circumference, with a breaking strain of 2 J 

 tons. The 1,000 fathoms next the dredge were hawser laid, 2 

 inches in circumference. Russia hemp seen..s to be the best 

 material for such a purpose. Manilla is considerably stronger 

 for a steady pull, but is more likely to break at a kink. 



The frame of the largest dredge used weighed 225 pounds. 

 The bag was double, the outside of strong twine netting, lined 

 with canvass. Three sinkers, one of 100 pounds, and two 

 of 56 pounds each, were attached to the dredge rope at 500 

 fathoms from the dredge. A description of the sounding made 

 in the Bay of Biscay on the 22d of July, 1869, will give an 

 idea of the process. When the depth 'had been ascertained, 

 the dredge was let go about 4:45 P. M., the vessel drifting 

 slowly before a moderate breeze. At 5:50 P. M. the whole 

 3,000 fathoms of rope were out. While the dredge is going 

 down the vessel drifts gradually to leeward ; and when the 

 whole 3,000 fathoms of rope are out, she has moved so as to 

 make the line from the dredge slant. The vessel now steams 

 slowly to windward, and is then allowed to drift again before 

 the wind. The tension of the vessel's motion, thus instead of 

 acting immediately on the dredge, now drags forward the 

 weight, so that the dredging is carried on from the weight and 

 not directly from the vessel. The dredge is thus quietly 

 pulled along, with the lip scraping the bottom, in the position 

 it naturally assumes from the center of weight of its iron frame 

 and a~ms. If, on the contrary the weights were hung close to 



