Backhoe- or Dipper Dredger (BHD)
The Backhoe Dredger is typically a hydraulic excavator as known from land-based machinery. For dredging purposes, and considering the larger machines, such a hydraulic excavator is mounted on a dedicated dredging pontoon. This dedicated dredging pontoon mostly has 3 spudpoles, enabling a partial jacking-up of the pontoon for a stable working situation. This stable working position allows the effectuation of high cutting forces, precise digging and positioning, and increases safety.
Backhoe Dredgers offer a relatively high cutting force, so they can be deployed in situations where unconsolidated soils, (weathered or exploded) rock, soils with cobbles and boulders etc. have to be dredged. Typically the dredged soils are loaded in a hopper barge moored alongside the BHD, allowing regulated transport and discharge.
Compared to other dredging techniques like f.e. Cutter Suction Dredgers or Trailing Suction Hopper Dredgers, the production capacity of BHD’s is relatively low.
The typical dredging depth of Backhoe Dredgers is approximately 20 meters below water surface, sometimes extendable till ca. 30 meters below water surface (but then reducing production capacity considerably). Some very large BHD’s can dig even deeper.
Smaller examples of Backhoe Dredgers can be placed on pontoons using their original undercarriage. This enables the use of the excavator for land-based deployment too, but obviously is not a sturdy unit as in case of the fixed mounted version. For these smaller versions pontoons allowing partial jack-up are also available (and recommended). For very small excavators also non- jack-up pontoons are sometimes used, using spudpoles for fixation of the position only, while the pontoon still floats. This configuration is not advisable, as the working platform for the excavator is not stable, thus not allowing exact digging and not offering a safe working situation.