202 



A TREATISE ON DRKDdKS AND DREDGING 



Another method used for unloading scows is by means of a 

 grab bucket dredge. In this case the debris from the scow is picked 

 up by the bucket, which can be of the clamshell or orange peel 

 type, and dumped either directly on land or into cars, running on 

 tracks laid parallel to the shores. This method cannot be used, except 

 when the difference of level between the water and the surrounding 

 land is slight, and the materials must be raised only a short height. 



When the dredged materials in the scows must be raised to 

 a greater height, a grab bucket attached to a hoisting and con- 

 veying machine will be found more convenient. The apparatus 

 in this case will consist of a solid scaffold firmly fixed on shore. 



FIG. 71. Grab Bucket for Unloading Barges. 



On this scaffold is mounted an inclined cantilever beam with one 

 end projecting well over the river so as to permit the bucket to 

 be over the scow, while the other end extends over the land. The 

 cantilever is inclined toward the river, thus leaving a large space 

 for the bins on the land side. The grab bucket travels along the 

 cantilever suspended to a small truck. The bucket is attache* I to 

 the end of the hoisting cable and raised to the underside of the 

 cantilever, when a hauling cable moves it along the whole length 

 of the cantilever. The bucket of the usual capacity, varying 

 between \ and 1 cu.yd., is opened and closed as explained for 

 the grab dredges when the bucket is commanded by a double- 

 chain system. The cantilever on the land side is of such height 



