GRAB DREDGES 173 



of the material to be dredged. When the scoops are made of 

 steel plates with sharp edges, we have a closed solid bucket 

 convenient for working through such loose materials as quick- 

 sand and mud. For working through clay a bucket in which the 

 edges of the scoops are provided with tines, Fig. 50, is considered 

 the most suitable. For dredging through hard sandy material 

 the edges of the scoops are furnished with interlocking tines set 

 close together. Finally for raising boulders, gravel, and blasted 

 d6bris an open-tined grab is used built in the manner shown in 

 Fig. 51. The buckets herewith represented are those constructed 

 by Messrs. Rose, Downs & Thompson, Ltd., being similar in their 

 outlines to others built by European manufacturers. In America 



FIG. 50. Grab Bucket for Dredging FIG. 51. Grab Buckets for Gravel 



through Clay. and Boulders. 



only the solid closed bucket is used. This is due to the fact that 

 there is a tendency here to use buckets of as large dimensions as 

 possible, hence the penetration into the soil is accomplished by 

 means of the great weight of the bucket itself, instead of being due 

 to the shape and arrangement of the tines located at the edges of 

 the scoops. 



The clamshell bucket has an overhead iron rectangular frame. 

 At the lower end of this frame are pivoted the two parts of the bucket, 

 and the cross-head piece regulates the chains. These iron frames, 

 together with the manner of attaching the two parts of the bucket 

 to the frame, and the device for opening and closing the bucket, 

 form the chains of the numerous patents. 



Owing to the fact that the efficiency of the machine is estimated 

 at one bucket per minute, American contractors have rapidly 



