142 A TREATISE ON DREDGES AM) DKKDGING 



and I860 the channels were cleared by raking or harrowing the 

 bottom, and they remained cleared as long as operations wero 

 continued, while as early as the years 1837 and 1839 the use of 

 dipper dredges served by scows proved a failure, since in a one night 

 storm all the materials that had been removed after a great expen- 

 diture of time and money were brought back. For this reason 

 Major M. D. McAlester, U. S. A. Corps of Engineers, in the report 

 of the Chief of Engineers for the year 1366, states that the plan of 

 stirring up the sediment forming the bars within the limits where 

 greater depth of channels is required is most efficacious and eco- 

 nomical. 



In the harrowing process, successfully applied in the 50's the 

 machine consisted essentially of a wooden frame of rectangular 

 shape, one end of which was attached horizontally to the stern of 

 a sidewheel steamer and turned about a horizontal axis, while the 

 other contained the iron teeth for harrowing and was held in contact 

 with the bottom of the channel, and raised entirely out of order, 

 as necessity called for, by means of tackling rigged to shears resting 

 on the deck of the vessel. In using this machine many interruptions 

 of work occurred, owing to the necessity of repairing the parts of 

 the rake damaged in consequence of impact with wrecks. 



On the same principle more powerful machines were constructed 

 later on and used in different sections of the Mississippi River. 

 Thus, for instance, in the year 1867 an appropriation of $96,000 was 

 made for the construction of two dredges, the "Montana" and the 

 lt Caffrey " to be used on the upper Mississippi River between St. Paul 

 and the mouth of the Illinois River. The dredges were sidewheel 

 steamers. The " Montana " was 210 ft. long, 35 ft. beam and 5J depth 

 of hold, and was equipped with two engines having 20-in. cylinders 

 and 7-ft. stroke; while the "Caffrey" was 150 ft. long, 30 ft. wide, with 

 4-ft. hold, with a draft of 32 in. She had 15-in. cylinders with 

 5-ft. stroke. These dredges were equipped with scrapers designed 

 by Col. Long. These scrapers consisted of a frame attached to the 

 bow of the boat and carrying a heavy crossbar to which were attached 

 six steel buckets or cutters. This frame could be raised or lowered 

 at will. In operating, the boat went to the upper side of a reef, the 

 scraper was lowered and the boat was then backed slowly down- 

 stream, scraping the sand with it down to deep water below the reef. 

 This operation was repeated until the desired depth was obtained. 



This scraping was continued for several years at a cost of about 



