158 A TREATISE ON DREDGES AND DREDGING 



There are numerous conditions which tend to greatly alter this 

 estimate, and that must be considered. The presence of stumps, 

 and boulders in the ground will retard the work of the dipper dredges. 

 Working through plastic and sticky clay the progress is retarded, 

 owing to the fact that the clay sticks in the bucket for some time 

 after the door is opened before it falls through. A dipper dredge 

 employed to dig canals through marshy land, cutting its own way 

 and depositing the debris on both sides so as to form the ditches, 

 will do a larger amount of work than if used in places in which the 

 debris is placed in scows. The handling of scows by tugs frequently 

 causes delays, similar to those caused by trains in steam-shovel 

 work. Then, too, less work is done when only a few feet of exca- 

 vation is necessary. 



The following examples serve to illustrate the work dipper 

 dredges will do. In one section of the Chicago Drainage Canal 

 five dipper dredges of 2 cu.yds. capacity were employed for dredging 

 through hard clay. The best week's work for four dredges was 

 an average of 1070 cu.yds. per 10-hour shift, while one dredge 

 reached an average of 1530 cu.yds., thus obtaining an average effi- 

 ciency of nearly one bucket per minute. Capt. D. C. Kingman, U. S. 

 Engineer Corps, reports that at Sodus Bay, N. Y., with the Osgood 

 Dredge " Frontenac " 1J cu.yds. dipper, from June 26 to 30, 1892, in 

 45 hours of actual work 4390 cu.yds. of sand and gravel were dug, 

 an average of 97 cu.yds. per hour, or about one bucket per minute. 

 On the Raritan River, N. J., the dredge " Alpha," with a dipper of 

 1 cu.yd. capacity, armored with teeth so as to work through rock, 

 in the month of September, 1889, working 207 hours, excavated 

 12,050 cu.yds. of shale rock and gravel; it averaged 60 cu.yds. per 

 hour and consequently at the rate of one bucket per minute. 



In Engineering News, February 28, 1901, a report is given of the 

 trial of the dredge "Chicago," with an 8-cu.yd. dipper, working in 

 sand and clay in 25 ft. of water, excavating in 30 minutes 385 cu.yds. 

 of material. This would represent 12 cu.yds. per minute, or one 

 bucket and a half. But it was on a trial performance and not on 

 regular work, being a new machine working only half an hour. 

 However, it is fair to assume from this that large dredges can dig a 

 dipper full per minute. 



The output of the dipper dredge depends also upon the locality 

 in which the machine is working. For instance the output of dredges 

 working in wide rivers or bays, where they are not interfered with 



