254 A TREATISE ON DREDGES AND DREDGING 



of coaling and repairing the dredges, office expenses and other 

 items. These are not charged to dredging in the government 

 reports, while they are very expensive items to a contractor. 

 Another item which the government reports do not show is the 

 contractor's profit, which must cover his own work and the risks 

 he must incur. Also, the interest of the money invested in the 

 plant is given too low in the government reports, as it is evident 

 that a private contractor cannot obtain money at the same low 

 interest as the government. Hence even the accurate data furnished 

 by these annual reports should be handled with great care by 

 engineers and contractors. 



The proper way to correctly determine the cost of dredging is to 

 make an accurate analysis of all the items of expense required for 

 the work under consideration. The expenses of dredging may be 

 classified in two groups, namely: those concerning the plant and 

 the general expenses required for the execution of the work. In 

 regard to the plant the expenses can be again divided into operating 

 expenses or those required every day for the running of the dredge, 

 and into yearly expenses, being interest and depreciation on the 

 plant and interest on the capital invested. These must be prorated 

 over the length of the season worked. 



Operating Expenses. The field or operating expenses include 

 all the expenses required for running the plant in such a manner 

 as to obtain the greatest efficiency with the minimum effort. 

 The operating expenses include those absolutely necessary for the 

 removal of materials from the bottom, as well as those required for 

 the transportation of the dredged materials to their final destination. 

 Thus the operating expenses vary with the machine employed 

 and the method of transportation of the debris. In the hydraulic 

 dredges as well as in the dredges of the sea-going hopper type the 

 principal expenses are those required for the handling of the machin- 

 ery to keep it in perfect working order; but when the materials 

 must be transported on scows, towed by tugboats, besides the running 

 expenses as indicated above, there is also the cost of hauling the 

 scows. Thus in regard to the operating expenses a distinction 

 should be made concerning the character of the machine employed 

 as dredges of the hopper type; dredges in which the transportation 

 of the material is effected by scows towed by tugboats, and dredges 

 in which the debris is conveyed to land by means of pipes or other 

 devices. 



