CHAPTER XXI 

 GRAB DREDGES 



ANOTHER intermittent dredge is one equipped with grab buckets. 

 This machine is considered one for great depths, as it is able to 

 excavate at places out of reach of any other machine. The ordinary 

 grab dredge consists of a steel bucket in the shape of a grab, capable 

 of picking up large boulders and soft materials and usually worked 

 by a steam crane, which lets the open grab down to the ground to be 

 excavated and then closes it by a chain, which forces the tines into 

 the ground. The grab is then raised by the crane and the contents 

 are deposited on the sides of the excavation or into barges to be 

 carried to the dumping place. 



The grab bucket dredge is a very convenient machine and can 

 be adapted to a large variety of work. In spite of its simplicity it 

 is a useful machine. Any contractor can easily build one of them. 

 By mounting on a float or scow any locomotive crane or derrick 

 with its necessary engines, and by attaching a grab bucket to the 

 hoisting rope or chain, a dredge is obtained. A machine of this class 

 does satisfactory work on the improvement of small harbors and rivers 

 and is extensively used throughout the English Colonies. Besides 

 the common use of dredging the bottom of canals, rivers and harbors 

 for navigation purposes, the grab bucket dredge can be used for 

 digging gold, oysters, pearls, corals and sponges from great depths. 

 In a word its many uses make it a very convenient machine. 



The first grab dredge built was perhaps the one designed by 

 Fr. Domenico Ferra and used at Savona in 1773; but the machine 

 as now used was first constructed and extensively used in America, 

 and then introduced into England and her Colonies. There is a 

 difference between the grab dredges built in America and those 

 constructed in England in the mounting and handling of the bucket 

 as well as in the capacity. 



The American grab dredge is constructed as follows: The 

 machine consists of a strongly built A frame mounted on a boat and 



168 



