SEA-GOING HYDRAULIC DREDGES 



113 



in November, 1871, during which period .734 of a cu.yd. of sand 

 per minute was removed. During the month of February, 1872, 

 1.127 cu.yds. per minute were removed. The greatest quantity 

 removed on any one day was 770 cu.yds. or at the rate of 1.26 cu.yds. 

 per minute. 



The average cost of dredging and dumping the sand for the whole 



FIG. 32. Cross-section of the Dredge "Thomas," showing Central Pit and Lateral 



Hoppers. 



period of 7 months was 53 J cents per cu.yd., the least cost during 

 any entire week was 19 cents per cu.yd., and the least cost for any 

 one day was on May 14, 1872, when 770 cu.yds. were removed hi 

 10 J hours, at a cost of only 13 cents per cu.yd., the time actually 

 occupied in pumping being only 5} hours. With some modifications 

 in the machines the cost of dredging would not exceed 10 or 11 

 cents per cu.yd. inclusive of running expenses, wear and tear of 



