STATIONARY AND HIGH-TOWER LADDER DREDGES 



85 



Stationary ladder dredges are those without propelling apparatus. 

 They are towed from place to place and the small movement required 

 to follow the progress of the work is obtained by paying in and out 

 the various ropes attached to the four corners of the boat and moored 

 to distant points. Stationary ladder dredges of American construc- 

 tion are usually provided with three or four spuds so arranged that 



FIG. 20. Dredge on the Rhone River Propelled by Sprocket Wheel. 



when lowered the dredge will remain strongly fixed to the bottom. 

 An advantage derived from using spuds consists in obtaining a 

 machine that can be swung around one spud as center of rotation, 

 thus dredging in great arcs or circles. 



The hull of the stationary ladder dredge can be made of any 

 shape, but as a rule it is made with a flat bottom like any ordinary 

 float. The hull, however, is provided with the ladder pit, tower, 

 bucket chain, boiler and engines similar to those used in the sea-going 

 and semi-sea-going ladder dredges, with the only difference that all 

 the machines are mounted on deck. Accommodations are not pro- 

 vided for officers and crew, as the men remain on board only 

 during the working hours. The vessel is, as a rule, of very light 

 draft and able to navigate and operate in very shallow waters. 



Fig. 21 shows an ordinary stationary ladder dredge built by 

 A. F. Smulders of Schiedam, Holland. 



