180 A TREATISE ON DREDGES AND DREDGING 



circulated through them. The frictions were set up by steam 

 compressors, so arranged as to apply pressure graduated at the 

 will of the engineer. From the drums four IJ-in. 37-wire strand 

 plow-steel cables ran to the clamshell. This clamshell bucket 

 was itself of rather novel construction, as shown by Fig. 56. The 

 bucket was of 10 cu.yds. capacity, and when empty weighed over 

 30,000 Ibs., and as the great depth of water precluded the use of 

 poles, some special precautions were taken to prevent it from twisting 



FIG. 56. 10-cu.yd. Clamshell Bucket of the Dredge "Finn MacCool." 



the cables together. The method adopted, as seen from Fig. 56, 

 was to employ two sheaves, one placed on each side of the bucket, 

 and to operate the bucket by two opening and two closing cables. 

 As these four cables ran over four sheaves on the boom, and the 

 cables were made in pairs, with right- and left-hand lay, there was 

 no tendency of the bucket to twist. 



The secondary engines were two in number, each being a double- 

 cylinder engine, and one being placed aft and the other forward 

 of the main engine. The forward engine was 10x12 in. and drove 

 three friction drums for handling the forward anchor lines and 



