108 A TREATISE ON DREDGES AND DREDGING 



entering from the holes. In this manner the materials stored 

 in the hoppers can be transported to any place. To dump the 

 debris one set of small flaps is open at a time ; the contents of the 

 compartment of the hopper will fall into the chamber and the material 

 mixed with water will be in condition to be raised by a sand pump. 

 This pump will also force the material through a discharge pipe, 

 thus conveying the debris to land. In case the quantity of water 

 entering from the holes is not sufficient to dilute the material, water 

 is taken from the tank on deck. 



In regard to the dredging apparatus the hydraulic hopper dredges 

 can be built either with a single suction pipe and a centrifugal 

 pump located amidship, when the hull is provided with a well for 

 the suction pipe like in the dredge "Thomas"; or the dredge is 

 constructed with two centrifugal pumps, one located on each side 



FIG. 30. Sand Pump on Dredge "Nereus." 



of the vessel and alimented by a suction pipe, each pump discharging 

 into a separate hopper. In this manner are built the dredges for 

 the Seine River and those of the U. S. Government employed 

 in the Ambrose Channel in New York Harbor. The ends of the 

 suction pipes may be furnished with either a simple grating or an 

 excavator of the drag or cutter type. When there is only a grating 

 or a drag the suction pipe is inclined toward the stern, while when 

 there is an excavator the suction pipe is feeding forward and is 

 inclined toward the bow. Since the hydraulic hopper dredge is 

 usually designed to work in places exposed to stormy weather and on 

 account of its great running expenses it must work even in heavy 

 seas, special attention should be given to the joint of the suction 

 pipe of the pump in order that the dredging be not affected by the 

 rolling of the vessel and without straining the joint to such an 

 extent as to impair its safety. 



From the reason that the dredging operations should be con- 



