Development of Advanced Dredger

The "Dredger" was developed as a specialized vessel for improving the water quality of lake Kasumigaura by dredging its muddy bottom ooze. Unlike normal dredging with a dredger, ooze dredging is a dredging operation performed under difficult constraints, namely, removing only the very oozy sludge built up on the surface layer of the lake bottom (about 30 em thick) having a water content rate of 200-400% and including much phosphorus and nitrogen. Up till now, ooze dredging has presented many problems: because the mud content ratio is low and has a wide variation and the positioning of the ship and operation of the ladder is done by hand, ooze dredging has been of poor precision with the dredging being either too deep or too shallow, and the operating efficiency has been low because the actual mud lifting time amounts to only a small fraction of the dredging time, and many workers are required. By working to overcome these technical problems, developing and improving the dredging equipment, and developing a dredging automatic control algorithm to greatly automate the operations, an automated dredger dubbed the "Kasumizaurus" has been completed. The automated system is divided broadly into an automatic control part for the dredging operation and an operation monitoring part for the operation of work management. The Kasumizaurus, which began operation in March 1995, is designed to be considerably better than a conventional ship in dredging efficiency, high-mud-content-ratio dredging, operational precision, and labor saving.