GRAB DREDGES 



175 



the cams to which are attached the power chains. The capacity 

 of the bucket varies from 1 cu.ft. to about 10 cu.yds. Figs. 52 and 

 53 represent one of the orange peel buckets as built by the Hayward 

 Company of New York. 



The orange peel bucket is seldom used for dredging purposes 

 while the clamshell bucket seems to be in favor with engineers 

 and contractors. However, grab dredges with orange peel buckets, 

 are used in the improvements of small rivers in which the dredged 

 materials are deposited on both shores. For such work, however, 

 the dipper dredge would be more efficient and economical. The 

 grab dredge is the machine for great depths, and it is only under 

 such conditions and when no other machine could be employed 

 that the grab dredge can be used to great advantage. 



Grab buckets, both clamshell and orange peel, are now designed 

 to pick up hard materials, such as rocks and stumps. Some of the 

 best designs will hold so tenaciously to a stump as to pull it loose. 

 The fact that such dredges will do this work in deep water means a 

 decided advantage. 



The bucket of the grapple dredge can be operated in two different 

 ways either by a single or a double line. When 

 one line is used this performs all operations of 

 opening, closing, raising and lowering the bucket, 

 while when two lines are employed, one is for 

 closing and hoisting the bucket and the second 

 for opening it. 



With a single line, it passes over a sheave at 

 the top of the boom to the drum of the hoisting 

 engine. The chain, after passing through a hole 

 in the fixed discharging hook, which is sus- 

 pended from the boom head, is wound around 

 and fixed to a sheave within the bucket. The 

 operation of the machine is very simple; the 

 bucket is lowered open, and the action of raising 

 closes it. When raised the discharging hook 

 opens the bucket, which empties and is then 

 lowered for a fresh operation. The discharging 

 hook is suspended either by chains or wire 

 ropes or by bars; in either case they are capable of adjustment so 

 as to regulate the height of discharge. There is on the market a 

 very large variety of discharging hooks which together with the 



FIG. 54. Cooper & 

 Holdsworth's Sin- 

 gle-chain Attach- 

 ment. 



