CHAPTER XIV 

 SEA-GOING HYDRAULIC DREDGES 



SEA-GOING hydraulic dredges are of two types, those in which 

 the hull is built like that of any ordinary steamer, having on board 

 all the required machinery and accommodation for the crew, and 

 those in which the hull is of larger dimensions to provide room for 

 the hopper to store the excavated material. The former type of 

 dredge is simply an excavating machine, while the latter type can 

 be considered as an excavating and transporting machine. Consid- 

 ering these two types of dredges from the point of view of excava- 

 tion, they are identical, the only difference being that in one 

 case the debris is conveyed into the hoppers by means of a chute, 

 while in the other case the chute conveys the materials to the sides 

 so as to be loaded into scows. To avoid a useless repetition only 

 the hydraulic dredges of the hopper type will be discussed. 



The sea-going hydraulic hopper dredges perform the double 

 function of dredging and transporting the debris so as to be dumped 

 in convenient places, into deep waters. In order to unload the debris 

 away from the shore so that the tides will not bring back any 

 part of it, the steamers generally go not less than 8 or 10 miles 

 from shore. For this reason their hulls must be strongly built to 

 stand well in any kind of rough weather. The hull is usually built 

 of steel, but there are several suction dredges used by the U. S. 

 Government for harbor and river improvements along the Atlantic 

 and Gulf coasts that have wooden hulls covered with copper plates. 

 Wooden hulls are preferred on work at shallow depths on account 

 of wood being more elastic than steel, the wooden dredge being 

 better able to resist the inevitable pounding on shallow bars. Hulls 

 are built of large dimensions in order to have large space for the 

 hoppers, thus carrying on each trip as much as possible of the dredged 

 materials. Yet these dimensions should be kept within certain 

 limits so as not to require extra heavy and expensive engines, which 

 tend to greatly increase both the original cost of the dredge and 



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