STATIONARY AND HIGH-TOWER LADDER DREDGES 89 



Quarters for the crew are provided on the upper deck and are 

 unusually spacious, light and well ventilated. 



The hulls are built entirely of Oregon fir, the dredge hull being 

 75 ft. long, 31 ft. beam and 6 ft. depth of hold. The intermediate 

 scows are 40 ft. long, 16 ft. wide and 3 ft. depth of hold, each carrying 

 belt conveyors 65 ft. long. The delivery scow is nearly triangular 

 in shape, being 31 ft. 4 in. long, 16 ft. 4 in. wide and 2 ft. deep at 

 the forward or receiving end and 33 ft. 4 in. wide and 4 ft. deep at 

 the after delivery end. The hull is given this unusual shape the 

 better to support the overhanging load of the delivery conveyor, 

 and to secure a greater angle of gyration when the scow is attached 

 to the dredge. The width of the hull was limited to allow it to pass 

 the locks, which are only 35 ft. wide. 



The contract stipulated that the dredge should have a capacity 

 of 250 cu.yds. per hour in ordinary digging. The first preliminary 

 test demonstrated that she could dig 400 cu.yds. per hour; and 

 she actually did dig 200 yds. in the toughest kind of clay and hardpan 

 under adverse conditions. Although at times the buckets, when 

 not full, carry considerable water, this flows back from the conveyors 

 into the river and the spoil is deposited quite free from water. The 

 crew of the plant now consists of 9 men, but can probably be reduced 

 eventually. The cost of operation, including fuel, is about $30 per 

 day, but the plant will undoubledly reduce the actual cost of dredging 

 over the old dipper dredge 50 per cent or more. The cost of wear 

 and tear cannot be determined, of course, until the dredge has been 

 operated about two seasons. The principal wear and cost, no doubt, 

 will be the rubber conveyor belts; but this will be minimized by 

 the comparatively small repairs to the machinery as compared with 

 a dipper dredge. 



One of the most difficult conditions in the operation of this 

 plant is the varying load, due not only to the varying depths of 

 water in front of the dredge or the varying face of the cut, but the 

 character of the material. Each requires a different adjustment of 

 the machinery, that is, a different speed of bucket chain and con- 

 veyors. This may vary in a single turn of the dredge, as sand, clay, 

 hardpan, or a mixture of these each act very differently. When a 

 uniform load of gravel or sand is to be moved, the operation is much 

 simplified. 



High-tower Dredges. When the dredged materials are used 

 for forming ditches or filling lowlands along the shore, the ladder 



