HINTS ON SELECTING DREDGES FOR VARIOUS WORK 51 



that may interfere with the dredges, whether it is dredging to reclaim 

 land, or to deepening channels, and many other considerations of 

 this character. One important item is the depth of the water and 

 the probable chance of storms. 



The character of the soil has much to do with the general type 

 of dredge to be selected, as whether a hydraulic dredge, a ladder or 

 dipper type is to be used. 



The suction or hydraulic dredge is better suited to work in soil 

 or material that is homogeneous, mattering but little whether it is 

 soft or compact, but it should not be excessively hard. Such materials 

 are sand, clay, earth, gravel and alluvial deposit, that are free from 

 large obstructions as boulders, snags, stumps and such things that 

 are not readily broken up with the cutter or agitator. 



When the material or soil is very compact and contains much 

 large gravel or small boulders, or is tough hardpan, ladder dredges 

 are better adapted than the suction dredge. Extremely large boulders 

 cannot enter the buckets so the ladder dredge must excavate around 

 them, leaving them to be taken out by other means. 



Grapple dredges will work in either hard material or in soft soil, 

 but more efficient work is done when the material is homogeneous. 



When the material is full of obstruction, whether the great mass 

 is soft or compact the dipper dredge is the most efficient machine 

 in use. 



When the material is such that it can be pumped through pipes 

 to the place of disposal, the suction dredge is ideal, unless the line 

 of discharge pipe interferes with the traffic. If the distance to trans- 

 port the dredged material is very short, a high tower ladder dredge 

 with a long chute can be used, but generally speaking when a ladder 

 dredge is used scows or barges are necessary to transport the exca- 

 vated material. For both the grapple and dipper dredge scows are 

 necessary unless the dredged material is deposited behind a nearby 

 bulkhead or is carried away by a system of belt conveyors. 



When the water is rough at the site of dredging, or if the scows 

 or pipe line interfere with the traffic of vessels, then the self-contain- 

 ing or hopper type of dredge should be used. The hydraulic hopper 

 dredge and the ladder hopper dredge as well as the combination 

 dredge are all described in this treatise. 



As a rule hopper dredges are sea-going vessels. In ordinary 

 weather they can work without anchorage. The dredge passes slowly 

 over the area to be dredged, picking up its load, and when the hoppers 



