CHAPTER X 

 LADDER OR ELEVATOR DREDGE. GENERAL DISCUSSION 



THE ladder or elevator dredge consists of a series of steel buckets, 

 attached to two parallel endless chains running along a trussed ladder 

 and revolving around two drums or tumblers, located at the extrem- 

 ities of the ladder. The ladder is kept in an inclined position, its 

 upper end resting on a tower mounted on the boat while the lower 

 end is under water, raised and lowered by chains. The dredging 

 apparatus together with all the required machinery is mounted on 

 a vessel which can be easily moved from place to place. The work 

 of the ladder dredge is easily understood. The steel buckets forming 

 an endless chain in passing around the drum at the lower end of the 

 ladder are brought in contact with the soil and scrape it. The 

 buckets filled with the removed material ascend the ladder and in 

 passing over the upper tumbler empty their contents into a chute 

 from which the material falls into scows of other receptacles and is 

 conveyed to distant points. 



The hull of the ladder dredge is made of different shapes and 

 materials, depending upon the work to be done. To insure stability, 

 it is desirable to have the hull of the dredge as wide as possible, and 

 yet in the sea-going dredges the hull should be made narrow and 

 long in order to insure seaworthy qualities in the vessel. The hull 

 can be made either of steel or wood. In dredges of small capacity 

 the hull is usually made of wood, but dredges of larger capacity, 

 as for instance all the sea-going dredges and also many of those 

 employed in the harbors or wide rivers, have the hull made of steel. 

 The advantages derived from employing steel hulls are: (a) that 

 the structure will be more solid and compact, (6) that the hull 

 built of stronger material will occupy less space thus leaving more 

 room for the machinery, (c) the vessel will be of lighter draft 

 and will be very stiff, thus avoiding vibrations that arc always 

 found in dredges with wooden hulls and dangerous on a machine 

 mounted on a float, since the continuous strong vibrations will tend 

 to disconnect the various parts of the machinery. 



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