TRANSPORTATION OF THE DEBRIS 191 



ments of rivers and canals in connection with the ladder, dipper 

 and grab dredges, when the material must be transported to a certain 

 distance and raised again by some machine. In such a case the 

 sides of the boat prevent the scattering of the material under the 

 stirring action of the lifting machine; but the platform forming 

 the bottom of the boat is subjected to hard usage and easily wears 

 out. 



In regard to the shape, the open-hold barges are built with 

 flat bottoms to insure steadiness and light draft, thus, too, making 

 their construction cheap. In barges of large dimensions the hori- 

 zontal beams or keelson are subjected to unusual stress, and it is 

 worthy of note that in the barges used for the transportation of 

 the rock excavated from the site of the new Pennsylvania Station 

 in New York city, all the beams of the floor of the barges, under 

 the double action of the pressure of waves below and the material 

 above, broke along the line of neutral axis. They showed a seam 

 as long as the beam itself, while the beam remained unaffected 

 on the upper and lower part, in apparent contradiction to the 

 well-known theory of tension and compression in the two parts 

 of the beams. 



Deck Scows or Pontoons. These are used for the transportation 

 of the dredged materials on rivers and canals, when the materials 

 deposited on deck of the barges have to be raised to be sent to the 

 dumping place. This type of barge is subdivided again into deck- 

 scows proper, railroad floats and deck-scows with open boxes. 

 The deck-scows are always built of rectangular design with flat 

 bottom to insure light draft, and they are made of soft wood both 

 in the frame and planking. 



The deck-scows proper are used for the transportation of the 

 dredged materials when they are deposited in skips which are lifted 

 by derricks or cranes and unloaded again, either directly onto the 

 ground or into cars to be conveyed to distant points. But this 

 method of transporting dredged materials is not very common, 

 and is used only under unusual conditions, as for instance on the 

 Fonage Canal along the Rhone River in France. 



When the dredged materials are used for filling lands some 

 distance from the shore instead of using skips it is more economical 

 to deposit the debris directly into railroad cars located on the deck 

 of a scow. For such purposes the deck of the pontoon is provided 

 with several parallel tracks upon which are placed the cars. After 



