REMOVAL OF BARS AND OTHER OBSTRUCTIONS. 43 



Their axes were horizontal, the salient angle being foremost. The flanges of the screws 

 were 12 inches wide at the base of the cones, and diminished to 6 inches at the points. 

 When these enormous screws were put in motion it was very difficult to guide the 

 boat. The material was readily plowed up, but it was not broken sufficiently fine to 

 be carried away by the current. 



Scrapers. " In 1867 there was appropriated the sum of $96,000 for the construc- 

 tion and operation of two scrapers or dredges on the upper Mississippi, between St. Paul 

 and the mouth of the Illinois River. The first efforts made to remove the sand-bars 

 by means of the scrapers, which were invented by Col. Long, was in the fall of that 

 year. These scrapers consisted of a frame attached to the bow of a boat and carrying 

 a heavy cross-bar, to which were attached six steel buckets or cutters. The 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 backed slowly down stream, scraping 

 the sand with it to the deep water below the reef. This operation was repeated until 

 the desired depth was obtained. Two side-wheel steamboats were equipped with 

 these scrapers by the Government, and, for a time, steamboat owners operated a scraper 

 boat between Keokuk and St. Louis at their own expense. 



" One boat was equipped and ready in October, 1867. Her first work was on a bar 

 near Gray Cloud, 17 miles below St. Paul. Only 3^ feet of draught could be carried 

 over this bar, and the regular packets could not cross it. After about four hours' work 

 with the scraper the depth was increased to 3^ feet entirely across the bar. The scraping 

 was continued for two days and a depth of 4 feet was secured. By November isth 

 all the bars between St. Paul and Prescott had been scraped and the depths increased 

 to 3^ or 4 feet. At that date the packet companies notified the engineer in charge 

 that the scraping had removed all obstructing bars and that no more work was required. 



" In 1868, when navigation again became difficult, the scrapers were put into com- 

 mission and worked throughout the season. They succeeded in deepening the bars 

 from 8 to 1 8 inches, and this was generally accomplished with a few hours' work. Beef 

 Slough was deepened from 3^ feet to 4^ feet in 35 minutes. 



" On the whole, the results were so satisfactory that steamboat owners announced 

 that their boats had been making regular trips without interruption, 'a condition of 

 affairs never before known at this stage of river in the experience of pilots of thirty-five 

 years' standing.' The largest steamers had been able to reach St. Paul in the low- 

 water season during two successive years, when without the aid of the scrapers they 

 would have been obliged to tie up. 



" This scraping was continued for several years at a cost of about $20,000 per annum 

 for each steamboat, but, as the relief was only temporary and had to be repeated from 

 year to year, it finally gave place to the so-called permanent improvement, consisting 

 mainly of channel contraction. 



" It should be borne in mind that in the portion of the river where the above-described 

 scrapers were used the obstructing sand reefs are quite short." 



