SEA-GOING HYDRAULIC DREDGES 



107 



been constructed hydraulic dredges in which the materials stored 

 in the hoppers can be transported to some point distant from the 

 vessel by means of pumping through a pipe line. In such a case 

 the bottom of the hopper is constructed in a different manner. 

 This new method was introduced in the dredge " Nereus," built by 

 Messrs. Smit & Sons for the removal of the bar of the Liffey in 

 connection with the improvements of Dublin Harbor. 



In the hydraulic hopper dredge " Nereus " the bottom of the 

 hopper is formed by two sets of flaps, Fig. 29; one of these open 

 in the usual way, being hinged to one side and controlled by 

 chains on the opposite end. At some distance above these flaps 



FIG. 29. Hoppers in the Hydraulic Dredge "Nereus." 



there are others which form the real bottom of the hopper. The 

 space between these two sets of flaps forms a chamber which can be 

 filled with water and for this purpose holes are left at the bottom 

 of the chamber. Water can be also supplied to the chamber by 

 means of a special tank located on deck. When the dredge is 

 operated as any ordinary hopper dredge the upper set of flaps 

 are left open and the debris will fill the chamber abutting directly 

 against the large flaps, and are dumped in the usual way by 

 simply opening these flaps. But when the dredge must trans- 

 port the debris to distant points and then pump it to land by 

 means of a discharge pipe the operation is made in a different way. 

 The small flaps are closed and form the floor of the hopper. The 

 large flaps are closed also and the chamber is filled with water 



