208 A TREATISE ON DREDGES AND DREDGING 



work in Lake St. Peter, and in a paper delivered before the Canadian 

 Society of Civil Engineers Mr. Robinson states the following con- 

 ditions were considered in her design and building: 



"It must be able to make a cut 900 ft. wide at one time tind 

 5 ft. to 10 ft. thick at one cut. 



"It must leave a clean and level bottom and cut mechanically 

 the entire area, as the material is blue clay and will not run or wash 

 like sand. 



"It must deliver the material sufficiently far to one side of the 

 channel to avoid any risk of washing back again. 



"The floating pipe line must be so arranged that it will freely 

 permit of the movements of the dredge, and that it will withstand 

 the wind and waves due to the locality, which are severe at times. 



"The dredge must be so worked that it will not obstruct the 

 channel for passing ships. 



" The anchorage and movements of the dredge must be so arranged 

 that the feed will be continuous and uniform. 



"The capacity to be a working rate of 2000 cu.yds. per hour. 



"The dredge must have ample coal supply, also provision for 

 a double crew." 



The contract price for this dredge was $103,800, not including 

 the discharge price or winches nor the alterations made. The 

 dredge was built by the Polsom Iron Works of Toronto, Ont., in 

 1901 and tested that year, but was not put to work until June, 1902. 

 Previous to this dredging had been done in Lake St. Peter by elevator 

 dredges. 



During the season of 1886 one such dredge excavated 886,710 

 cu.yds. for $25,723, or a cost for labor, coal, etc., of 2.9 cts. The 

 dredge "Lady Aberdeen/* with 1 cu.yd. buckets during the season 

 of 1901, excavated in 21 days at a cost of $3054.88, 120,600 cu.yds., 

 the unit cost being 2.53 cts. The actual working time was 246 hours, 

 thus an hourly output of 490 cu.yds. was attained. 



The first month, June, 1902, the "J. Israel Tarte" was put to 

 work; she excavated 93,750 cu.yds. This was accomplished in 

 41 J hours. Each month the output increased as the crew became 

 accustomed to the work. Thus in September 580,000 cu.yds. were 

 dredged, in October 600,000 cu.yds. The area covered in Septem- 

 ber was 7800 lin ft. by 325 ft., to an average depth of 5 ft. In 

 October a strip of the same width and depth but 8000 ft. long was 

 done. The dredge worked 126 working days in the season of 1903, 



