TRANSPORTATION OF THE DEBRIS 193 



American manufacturers are building dumping scows of very large 

 dimensions, not less than 200 ft. long and 40 ft. beam, divided 

 into four or five compartments, each shaped as an inverted frustum 

 of a pyramid with the floor formed by a trap door. This door is 

 hinged at one side and at the opposite side is controlled by chains 

 wound around a shaft, located on deck and parallel to the longi- 

 tudinal axis of the scow. This shaft, through a system of cogwheels, 

 is revolved either by a steam winch or by a capstan worked by hand 

 power. When the dumping place has been reached, the brakes 

 that keep the shaft in position are removed, the weight of the 

 materials pressing on the floor of the compartments opening the 

 doors and thus dumping the load. It is in closing the doors that 

 either the steam winch or the hand capstan comes into play. 



The European dumping scows as a rule are smaller than the 

 American, but are built of a large variety of designs. They are 

 generally provided with a central partition which divides the hold 

 into two separate longitudinal compartments. The shaft for the 

 opening and closing of the trap door is located on top of the central 

 partition. The advantage of such construction is that the doors 

 are smaller, consequently less strain is placed on the brakes which 

 keep the doors fastened. Even these two longitudinal hoppers 

 are usually subdivided into others, every one of them being in the 

 shape of an inverted frustum of a pyramid. But the shape of 

 these hoppers varies with the material to be transported ; thus, for 

 clay, the sides of the hopper should be kept as vertical as possible 

 to prevent the material sticking and clogging the doors, as they 

 would if the sides were inclined. For the transportation of fine 

 sand and mud the bottom of the hoppers, instead of being provided 

 with doors, have conic valves fitting circular openings. By simply 

 raising these valves the materials will immediately escape through 

 the openings. 



Fig. 62, A and B, show the cross-sections of two different types 

 of dumping scows employed on the construction of Suez Canal. 

 These scows were constructed with flat bottom in order to have 

 light draft; but when the material has to be dumped in deep 

 water in the high sea the scow is constructed with a hull similar 

 to any sea-going boat. Fig. 63, shows the cross-section of a dump- 

 ing scow constructed to convey and discharge dredged materials into 

 shallow waters. In such a scow should the trap doors form the 

 floor as usual, and open downward, they would reach the bottom 



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