256 



A TREATISE ON DREDGES AND DREDGING 



Repairs represent another important item of expense. They 

 should include only the repairs that occur almost every day and 

 are necessary for the continuous working of the machine. They 

 do not include the general overhauling of the dredge, generally 

 done once a year or at the close of the season. Mr. Babcock, dis- 

 cussing this item of expense in connection with the hydraulic 

 hopper dredges "Manhattan" and "Atlantic" states that the value of 

 the time lost due to repairs far exceeds the actual cost of the repairs. 

 He calculates that the value of time lost by reason of repairs in 

 eleven months was $110,538, while the money actually paid for 

 these repairs was only $43,721. 



The total amount of the operating expenses in a month, season 

 or year divided by the total quantity of material removed in the 

 same length of time, will give the cost of the unit of volume of the 

 excavated material. It is evident that all items of expense remain- 

 ing the same, the greater the amount of material excavated the 

 smaller will be the cost per unit of volume. Numerous delays 

 from various causes tend to increase the cost. Thus it may be 

 said that the operating expenses, per unit of volume, are inversely 

 proportional to the quantity of material removed, and directly 

 to the delays. The following table, taken from Engineering, June 

 19, 1903, shows the percentage of time worked and the delays for 

 an average of one year's work, of several dredges of different types 

 employed on improvement work in New South Wales: 



For the time occupied in the various operations by the hydraulic 

 hopper dredges "Manhattan" and "Atlantic," working eleven months 

 each, from July 1, 1905, to May 31, 1906, as given by Mr. Babcock, 

 in Engineering News, see Vol. LVI, p. 306: 



