64 A TREATISE ON DREDGES AND DREDGING 



recent years, as a rule, it may be said that in the extensive harbor 

 and river improvements only two types of dredges have been used, 

 these being the single-bucket dredge, either of the dipper or grap- 

 ple type, and the hydraulic dredge. The former is used in the exca- 

 vation of soils that are hard and compact, while the latter is employed 

 in very loose soils, as mud and sand. The powerful ladder 

 dredge, so extensively used in all the foreign countries, has had but 

 little use here. Such a disregard for one of the most efficient machines 

 exposes the American engineers and contractors to severe criticism. 

 Mr. A. W. Robinson has given some reasons that have induced 

 the American to use these two types of dredges in preference to the 

 ladder. In a new country more important improvements were 

 required at first than dredging, and consequently the little dredging 

 that was occasionally done in keeping the rivers and channels open 

 to navigation was not done directly by the Federal Government, 

 but given out on small contracts. Work was scattered along an 

 extensive sea coast and done at different times, according to the 

 necessity of the improvements and the small appropriations made. 

 Consequently the contracts were small and there was no certainty 

 of continuous work. Thus the dredging contractors found it more 

 advantageous to work the cheapest machines even if it life was short. 

 For this reason, until very recently the dredges employed in this 

 country were mostly of the single-bucket type, as the original cost 

 was small and they were very efficient and easily handled. Besides, 

 they had the advantage of being used for other purposes than 

 dredging, as lifting piles, lowering concrete blocks, raising wrecks, 

 lifting boulders, loading scows, etc. The attention of the American 

 manufacturers has been devoted to the construction of the type of 

 dredges that were in demand. When, with the changed conditions 

 of the country more powerful machines were required, these were 

 constructed on the lines of the old ones, as dredgemcn were skillful 

 in their handling and the manufacturers had acquired great expe- 

 rience in their construction. 



It has only been within a comparatively few years that the merits 

 of the ladder dredge has been recognized in America. Even to-day 

 contractors seem loath to use this type of dredge. However, during 

 the past decade the Canadian Government has built a number of 

 such dredges for use on the St. Lawrence River, and the Federal 

 Government has rebuilt and used with great success some of the 

 small ladder dredges used by the French on the Panama Canal. 



