![]() ![]() They are equipped with twin propellers and twin rudders to provide the required maneuverability. During dredging operations, hopper dredges travel at a ground speed of from 2 to 3 mph and can dredge in depths from about 10 to over 80 ft. Hopper dredges are classified according to hopper capacity: large-class dredges have hopper capacities of 6000 cu yd or greater, medium-class hopper dredges have hopper capacities of 2000 to 6000 cu yd, and small-class hopper dredges have hopper capacities of from less than 2000 to 500 cu yd. Dredged material is raised by dredge pumps through dragarms connected to drags in contact with the channel bottom and discharged into hoppers built in the vessel. Hopper dredges have propulsion power adequate for required free-running speed and dredging against strong currents and excellent maneuverability for safe and effective work in rough, open seas. They are equipped with propulsion machinery, sediment containers (hoppers), dredge pumps, and other special equipment required to perform their essential function of removing material from a channel bottom or ocean bed. Hopper dredges are self-propelled seagoing ships of from 180 to 550 ft in length, with the molded hulls and lines of ocean vessels (fig. Types of dredges used and estimated quantities to be dredged by each District (FY 81).Ī. (5) Physical environment of and between the dredging and disposal areas. (2) Quantities of material to be dredged. (1) Physical characteristics of material to be dredged. Selection of dredging equipment and method used to perform the dredging will depend on the following factors: Removal of loose or hard, compacted materials by cutterheads, either for maintenance or new work projects.ī. (3) A combination of suction and mechanical dredging. Removal of loose or hard, compacted materials by clamshell, dipper, or ladder dredges, either for maintenance or new work projects. Removal of loose materials by dustpans, hoppers, hydraulic pipeline plain suction, and sidecasters, usually for maintenance dredging projects. However, there are basically only three mechanisms by which dredging is actually accomplished: The category of “other” dredges in Figure 3-1 includes dipper, ladder, and special purpose dredges. Principal types of dredges include hydraulic pipeline types (cutterhead, dustpan, plain suction, and side caster), hopper dredges, and clamshell dredge. The dredging methods employed by the Corps vary considerably throughout the United States. The types of equipment used, by both the Corps and private industry, and the average annual amount of dredging associated with each type are shown in Figure 3-1. Factors Determining Equipment SelectionĪ. Guidance is provided for selection of the best dredging equipment and techniques for a proposed dredging project to aid in planning and design.ģ-2. This chapter includes a description of the dredging equipment and techniques used in dredging activities in the United States and presents advantages and limitations for each type of dredge. For a complete version of this document click here. ![]()
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