CLASSIFICATION AND CAPACITIES OF DREDGES 65 



These rebuilt dredges have by their work on the canal attracted the 

 attention of both engineers and contractors. The great field for 

 ladder dredges in America has been in the gold mining section 

 o.f the Western States. Although originally used for this purpose 

 in New Zealand, the idea was brought to the United States, and 

 the development of this type has been rapid. The buckets have 

 been increased in size until some of the latest machines use buckets 

 of f cu.yd. capacity. 



The hydraulic dredge is comparatively a very modern machine. 

 It was introduced on public work after the United States had grown 

 and work of great magnitude was necessary to keep apace with 

 the wonderful progress of the country. The navigable channels 

 were widened, the rivers and harbors deepened to accommodate 

 the modern and ever-growing leviathan of commerce, and in such 

 work the hydraulic dredges were found to be the most convenient 

 and efficient. They were used extensively in the harbors and bays 

 along the Pacific coast, and along the Atlantic shores they have 

 now almost supplanted the single-bucket dredges used in former 

 days. The great dredging work going on continuously in this country 

 in the last few years has aroused great competition among the 

 contractors, who have constructed powerful machines so to as obtain 

 competitive work and perform it at the smallest cost. Consequently 

 in America are now found the largest and most powerful dredging 

 machines in the world. But hydraulic dredges, although very efficient 

 in sandy soils, are not so efficient in hard soils. Heretofore such soil 

 has been excavated by the bucket type of dredge. 



The capacity of dredges varies exceedingly, and it is difficult to 

 give data as to the amount of material that can be excavated by 

 dredges of different types. The character of the material, the depth 

 of the water, the current and amount of traffic in the river, harbor 

 or channel, the size of the engines on the dredges, the size of the 

 pumps, buckets, or dippers all of these conditions and many more 

 affect the amount of work done. 



For instance a small elevator or ladder dredge of the hopper 

 type excavated 1400 cu.yds. of soft material in a 10-hour day, while 

 in average earth it excavated 1000 cu.yds., and in very hard 

 material 350 cu.yds. only. Hopper types of dredges always mean 

 reduced output, as the time is lost for digging that is consumed in 

 going to the dump. Inefficient scow service also serves to decrease 

 the output of the dredges. Many records could be given of indi- 



