CLASSIFICATION AND CAPACITIES OF DREDGES 61 



from one place to another under her own power, or the dredge is 

 moved by means of mooring lines and tugboats. Stationary ladder 

 dredges may be constructed with the ladder on one side of the 

 vessel or along the longitudinal axis of the boat; they may be 

 built with towers of the ordinary height or with high towers in 

 order to convey the debris to distant points along the shores. 



Hydraulic dredges may be classified as sea-going, which are 

 those able to steam from place to place under their own power, and 

 those employed in the improvement of canals and rivers. In the 

 sea-going dredges when the vessel contains large spaces for storing 

 the debris, it is called the sea-going hydraulic hopper dredge; but 

 when the hull is constructed similar to any other steamer without 

 reserved space for the debris it is called the sea-going hydraulic 

 dredge. The hydraulic dredges employed in the rivers and canals 

 may be either self-propelling or non-propelling, the latter being 

 the most commonly used, while the dredges employed in the improve- 

 ments of the Mississippi and other large rivers are mostly self- 

 propelling. These dredges, according to Mr. W. Robinson, may be 

 classified according to the location of their feeders into lateral, 

 forward, and radial. 



The process of removing a very loose soil from the bottom by 

 agitating the light particles so that they may be carried away by 

 water is not very extensively employed at present. However, this 

 stirring method has an historic interest and in some particular 

 work it can be employed with advantage even to-day. The stirring 

 of the material at the bottom may be obtained by means of different 

 devices which will be described later on; they are: the harrows, 

 the propellers, the converging revolving screws, jets of water, com- 

 pressed air, etc. 



Pneumatic dredges can still be considered in their experimental 

 stage. Only one type of these machines has been built so far and 

 this group of machine has no subdivision. 



Dipper dredges present more uniformity, both in the general 

 design and. construction than any other type of dredge. They 

 differ, however, in the material employed in the hull, in the dimension 

 and efficiency of the machinery, capacity of the dipper, length of 

 the handle and consequently depth of the reach, etc. But the large 

 variety of details does not change the main characteristics of the 

 machine, consequently subdivision cannot be made. 



Grapple dredges are of two different types, the clamshell and 



