4 A TREATISE ON DREDGES AND DREDGING 



discharge it into barges or conveyors so as to send it to its final 

 destination. The hydraulic dredge removes the material from 

 the bottom by means of a large centrifugal pump which draws the 

 materials, mixed with water, into a suction tube and forces them 

 to distant points by means of a long line of pipes. The stirring 

 dredges are those employed in the excavation of soils composed 

 of very finely divided particles; they agitate the soil and the material 

 thus brought in suspension is carried away by the action or current 

 of water. The pneumatic dredges are those in which the material 

 from the bottom is forced into the suction tube and thence into 

 the discharging pipe, by the action of continuous jets of compressed 

 air turned upward into the tube. 



Intermittent dredges are those provided with a single bucket 

 of large capacity, by means of which the material at the bottom 

 is raised to the surface and dumped into scows, to be conveyed 

 to distant points. All these various operations are made by the 

 bucket before it returns to the bottom to once more engage the 

 material. The single-bucket intermittent dredges are of two different 

 types, the dipper and the grapple dredges. The dipper dredge 

 is similar to the steam shovel used in land work, the only difference 

 being that it is mounted on a float, and the bucket is usually of 

 larger capacity. The grapple dredge is provided with buckets in 

 the shape of the clamshell or of the orange-peel, thus originating 

 two principal varieties of the grapple dredge, known as the clam- 

 shell and the orange-peel bucket dredges; These machines are 

 also mounted on floats and the capacity of the buckets is large. 



Transporting Excavated Materials. The materials raised from the 

 bottom of the water are transported to their final dumping place 

 by various methods. In the sea-going hopper dredges the materials 

 are stored in large bunkers and are carried to the dumping place 

 on board of the same steamer carrying the excavating machinery. 

 The debris can also be conveyed by means of belt conveyors or 

 pipes, or transported on floats and barges with closed bottoms 

 from which the materials are raised again by some device and sent to 

 their destination, or the scows are self-dumping, discharging the 

 debris into the deep water by simply opening the gates forming the 

 floor of the scows. 



A thorough knowledge of the various soils and machines is 

 necessary for successful dredging; and this depends exclusively 

 upon the fact that the best-suited machine should be used for the 



