Influence of Dredging Depth on Designing Cutter Suction Dredgers

1. Maximum dredging depth

The maximum dredging depth is an important design parameter of Cutter Suction Dredgers. Because in the cutter suction dredger, the flat boat and the positioning pile transmit the force generated when the cutter head excavates the soil to the soil, and the magnitude of the generated moment is proportional to the dredging depth. Thus, as the dredging depth increases, not only does the hull become larger and wider (in order to improve the stability of the hull), but the hull structure also becomes heavier. In addition, the dredging depth also has a significant influence on the reamer boom structure: for inspection, the reamer boom must be able to be lifted out of the water.

From the point of view of production volume, in order to obtain the required production volume, the depth of dredging determines whether it is necessary to install an underwater pump. Obviously, having a submersible pump increases the weight of the boom. If there is no submerged pump, the diameter of the suction pipe and the power of the dredge pump must be increased to reduce the concentration of the excavated mud-water mixture, thereby avoiding cavitation. But at the same time, it is very uneconomical to reduce the concentration of the mud-water mixture. According to the cavitation formula, a certain limited air separation pressure and maximum concentration value can determine whether a submerged pump is required and also where the mud pump should be placed underwater. Of course, there is still a question of economics, whether or not submersible pumps are suitable, submersible pumps are generally expensive (tightness requirements).

2. Minimum dredging depth

The minimum dredging depth shall be determined according to the draft of the pontoon, the location and shape of the cooling water inlet, and the structure of the cutter arm. It is obvious that barges must have sufficient bottom clearance even when working at minimum dredging depths. For large cutter suction dredgers this will result in a wider hull. The minimum dredging depth must be at least 1m less than the maximum draft of the hull. The design of the cooling water inlet must be suitable to prevent the entry of mud from the bottom.When dredging at the minimum dredging depth and the minimum dredging depth is shallower than the draft of the hull, it is necessary to select the appropriate shape of the reamer arm; otherwise, the arm will be dragged. To prevent dragging, the angle between the lower line of the arm and the horizontal should be at least 50°.