340 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



There is considerable difference of opinion as to the relative 

 merits of stationary dredgers attended by hopper-barges, ami 

 combined hopper and dredgers, conveying the dredged material 

 to the place of deposit. Mr. Messant has remarked that it has 

 yet to be proved, "first, that a ladder-dredging apparatus would 

 work with greater efficiency and economy if supported on a 

 vessel that happened to have a hopper attached to it, than if 

 supported by a vessel without a hopper ; and, secondly, that a 

 vessel with a dead weight of machinery, or amounting to 

 considerably more than the cargo, and with a crew much larger 

 than necessary for the purpose, could convey to sea a hopper- 

 load of dredged material at a cheaper rate than a vessel of only 

 sufficient capacity for its cargo, and with only a sufficient crew, 

 which would probably be about one-fourth of the crew required 

 for the hopper-dredger." 1 It is objected that, with the hopper- 

 dredger, owing to the constant moving, it is difficult to pick up 

 the same spot, face, or level on returning from a trip, con- 

 sequently the bottom is more likely to be irregular than if a 

 stationary dredger is used. 2 



Like other dredging appliances, the hoppeivdredger meets 

 special conditions where the stationary dredger, with its 

 attendant hopper-barges, would be inapplicable, or more costly to 

 work. Such as in cases when, owing to the range of tide, or 

 other causes, dredging can only be proceeded with during a 

 portion of a tide. The dredgers, crew, and vessel, would be 

 more advantageously employed in taking the dredged material 

 out to sea for deposit than in idly waiting for the time to 

 resume work, while the dredged material is being conveyed 

 away by other vessels and crews. In narrow, crowded channels 

 or areas, where hopper-barges alongside an ordinary dredger 

 would be inconvenient. In navigations of great length, where 

 small quantities of dredging may be required at intervals in 

 positions at long distances from each other. 3 In exj> 

 positions, where rough seas have to be encountered, and wh< iv 

 danger would attend the loading of hopper-barges alongside a 

 stationary dredger. 



Of the different types of dredging appliances in use, Mi-. 

 Webster, M.I.C.E., has given a very valuable description in a 

 paper laid before the Institution of Civil Engineers. 4 



1 M.P.I.C.R, Ixxxix. p. 102. 2 ItoV., p. 111. * H>'<1.. ]>- >"- 



* Ibid., p. 2. 



