212 



A TREATISE ON DREDGES AND DREDGING 



bow cable and two cables on each side of the vessel, see Fig. 71. 

 This permits a vessel to make a wide radial cut and to easily clear 

 passing boats. 



The "Tarte" is held in the same manner, which allows it to 

 work from one side of the channel to the other. To allow vessels 

 to pass, one set of side lines are slackened so that they drop on 

 the river bottom and the passing boats go over them. The pipe 

 line, which is about half a mile long, has ball and socket spring 

 joints between every pontoon. These pontoons are made of two 

 cylindrical air chambers, holding 100 ft. of discharge pipe between 

 them. The discharge end of the pipe is held in place by a winch 

 scow. When the dredge works on the side of the channel on which 

 the discharge is made, the pipe assumes, by floating on the pontoons, 

 a decided curve, but as the dredge passes to the other side of the 

 channel the pipe line straightens out, the operation only varying 

 the discharge end slightly, see Fig. 36. 



Both style of dredges work to a uniform bottom, cleaning up 

 as they go. When boulders are encountered the stone lifters are 

 used. In one case, when the cutter head of the " Tarte " broke off, 

 it was recovered with one of these boats. In addition to the sweep- 

 ing of the channel after dredging, the shallow channels are swept 

 once a year. 



Cost Data. In giving the following tables of costs, everything 

 is included except interest on the capital and depreciation. The 

 tables are self explanatory. The item of repairs includes keeping 

 the plant in good order, but not new or improved machinery. 



TABLE I 



Table I, gives for a term of eight years, material excavated, and 

 total cost for wages, supplies, new plant surveys and other details. 



