238 A TREATISE ON DREDGES AND DREDGING 



the elevator or ladder dredge is used the open-hold barge is the 

 standard type. 



For the efficient operation of the centrifugal pump it is necessary 

 that there be a large percentage of water in the sand. On the other 

 hand, it is necessary for the economical handling of the sand that 

 it be as free from water as possible. The decked barge with cargo 

 box has been designed to meet these conditions. The cargo box is 

 formed by fitting sideboards about 3 ft. high and arranging hopper 

 ends, inclosing nearly all the deck area, leaving but a small space 

 at each end for handling lines. The barge is placed alongside the 

 dredge and the mixture of sand and water from the centrifugal 

 pump is directed into the inclosed deck space. 



These decked barges are subject to very severe usage in the 

 operations of handling and unloading. The large sand companies 

 operating on the Mississippi River have installed unloading machinery 

 of the largest capacity with corresponding weight of parts. The 

 immense grab buckets come down on the deck with considerable 

 shock, causing heavy local stresses, so that the deck supports must 

 be close together and of ample section. In unloading, it is also 

 necessary at times to take out the sand very unevenly, such as 

 removing it from one end only, or from the middle, giving rise to 

 heavy longitudinal bending stresses, which must be provided for 

 by continuous longitudinal bulkheads. This service tells heavily on 

 the wooden barge, and its upkeep is a matter of considerable expense 

 and ultimate renewal after a comparatively short life. 



With the increasing use of steel for river-boat construction, 

 several steel-decked barges have been placed in service by one 

 of the largest sand companies on the Mississippi River. These 

 barges are 130 ft. long, 30 ft. wide and 7 ft. deep. A complete 

 steel deck is fitted, and on this a wood box is arranged by fitting 

 timber sideboards 3 ft. high. The deck beams are framed longi- 

 tudinally so as to better care for the impact of the grab bucket, 

 which is used with its cutting edges across the barge. Longitudinal 

 strength is secured by a system of lattice girders carried full length, 

 while the transverse strength is provided for by a system of cross 

 trusses. The deck beams are supported at close intervals by the 

 cross trusses, and by extra cross beams carried by the side frames. 

 Channel sections are used to a large extent in the funning, which 

 is spaced rather closely throughout the barge to insure strength and 

 stiffness. 



