SEA-GOING LADDER DREDGES 75 



officers and crew. Should also have on board a well-equipped repair 

 shop, so as to repair immediately the complicated machinery when 

 out of order. The steamer should have storage for a supply of 

 fresh water, coal and food, besides the interchangeable parts of 

 the various machines. 



Sea-going ladder dredges are built of two different types, viz., 

 the single and the hopper dredge. The single sea-going ladder 

 dredges proper consist of a strong vessel carrying all the dredging, 

 propelling, and other machines and boilers. The tower is located 

 amiclship with a central chute terminating on either side of the vessel 

 in order that the material may be easily discharged into scows. 



The hopper dredge is constructed in a similar manner, the only 

 difference being that the hull is much larger and between the tower 

 and the machinery there is a large space to hold several hundred 

 tons of material which enters the hopper by means of a chute. 

 The bottom of the hopper is provided with trapdoors controlled 

 by chains attached and revolving around two horizontal shafts, 

 so that the doors can be closed or opened at will. When the hold is 

 filled up with debris, the dredging operations are suspended and the 

 vessel goes out to deep water, where the doors are opened, and the 

 material will fall to the bottom by gravity. Then the vessel returns 

 and resumes its dredging operations. This machine, working con- 

 tinuously day and night, is provided with powerful illuminating 

 apparatus to make clear its way. 



The following description of the dredge "Ville de Rochefort," 

 taken from Engineering, illustrates the simple sea-going ladder 

 dredge. 



In 1897 the French Government intrusted to the important 

 firm of engineers at Lyons, MM. Satre, Fils Aine et Cie., the con- 

 struction of a powerful marine bucket dredge, with twin screws, 

 intended for deepening and maintaining the navigation channel 

 of the Charente. 



This river, on which is placed, at a considerable distance inland, 

 one of the five great military ports of France the port of Roche- 

 fort requires to be considerably deepened to allow the passage 

 of fully equipped ironclads between Rochefort and the sea. 



Not only is there a rocky bar at one point, but vast quantities 

 of mud are constantly being deposited on the river bed, seriously 

 reducing the available depth of water. 



For this reason the French Admiralty considered it necessary 



