CHAPTER XI 

 SEA-GOING LADDER DREDGES 



THE sea-going ladder dredges are those usually employed to 

 work in the open sea or for service in harbors. They are built to 

 sail under their own steam. Great care is necessary in designing 

 the hull of such dredges, as they should be even stronger than the 

 hull of ordinary steamers, in order to insure their stability against 

 the roughness of the sea and the strain of the work. For these 

 reasons the hull of the sea-going ladder dredges is always made of 

 steel, thus obtaining great stiffness and solidity. The hull is divided 

 into various compartments separated by water-tight bulkheads so 

 as to attain an unsubmergible vessel in case one of the compart- 

 ments should be invaded by water. 



The sea-going ladder dredges are self-propelling. They are 

 usually provided with two ordinary propelling screws located on 

 both sides of the stern or pit according to the type of the dredge. 

 Only ladder dredges of small capacity are furnished with a single 

 propeller; but it is always preferable to have two propellers even 

 in the small dredges of light draft. The propellers can be operated 

 by separate engines, or by the engines of the dredging machin- 

 ery; in such a case a single device permits of easily shifting the 

 power from dredging to the propellers and vice versa. 



In sea-going dredges on account of stability the tower is located 

 amidship and the ladder along the longitudinal axis of the steamer. 

 When the dredge is designed to work in deep water the ladder 

 remains in a well. The hull is closed forward, the ladder remaining 

 in tho bow of the steamer both in navigation and in dredging. AVhc'ii 

 the dredge is designed to work at varying depths, the ladder must 

 assume different inclinations and even be raised above the water 

 line; the pit is accordingly open and located aft. The boilers and 

 engines are located forward. In such a case the bow in navigation 

 becomes the stern in dredging. 



Sea-going ladder dredges moving continuously from one place 

 to another must be provided with commodious quarters for the 



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