106 A TREATISE ON DREDGES AND DREDGING 



its running expenses. Thus the capacity of the hoppers is kept 

 between 2000 and 3000 cu.yds. The hull is divided in different 

 compartments separated by watertight bulkheads. 



The hopper for the reception of the dredged materials is con- 

 structed in different manner. It generally consists of two rows of 

 bins located amidship on each side of the vessel in order to leave the 

 pit in their middle for the suction pipe as in the dredge " Thomas/ 7 

 or they are simply located side by side divided longitudinally as in 

 the dredge for the Seine River hereafter illustrated. The hoppers can 

 also be located one forward and the other aft of the vessel, separated 

 amidship by the space for the boilers and engines, as in the dredges 

 11 Manhattan " and " Atlantic." In such cases the hopper, being as 

 wide as the vessel, must be well braced and strongly built to resist 

 the pressure of the wet materials upon the walls of the wide hopper. 

 The bottom of the hopper is generally made in the shape of several 

 inverted frustra of pyramids for the purpose of facilitating the 

 descent of the materials by sliding along the walls of these pyramids. 

 The floor of each frustrum is formed by a gate or valve which can 

 be opened at will. These gates or valves are built of various designs, 

 the one most commonly used being in the shape of a flap hinged at one 

 side to the hull and operated by a chain at the free end. The chains 

 are attached to a horizontal shaft placed on deck and revolved by 

 a system of cog-wheels moved by an engine. By revolving this 

 shaft all the chains are drawn in or payed out, thus opening and 

 closing simultaneously all the various compartments of the hopper. 

 Conical valves are also used to close up the bottom of the various 

 compartments of the hopper. In such a case the four walls of the 

 inverted frustrum of the pyramid converges toward the bottom 

 and end in a circle strongly reinforced with iron rings. Into these 

 rings fit heavy conical shaped valves, and the various compartments 

 of the hopper are opened or closed by simply raising or lowering 

 these valves. The operation of dumping can be done while the vessel 

 is in motion. 



The materials removed from the bottom by hydraulic dredges 

 are always mixed with a large quantity of water in such a way that 

 the hopper will be found filled up with more water than solid mater- 

 ials. To avoid this the hoppers are always provided with several 

 overflows, to carry off the water. 



Besides hydraulic dredges with hoppers able to unload their 

 contents by gravity in the manner just described, there have also 



