Conceptual Design of a Submersible Remotely Operated Swimming Dredger (SROSD)

Increasing use of deep-water dredging and mining vehicles has been anticipated for resource collection, engineering construction and environmental protection. Existing deep-dredging or mining equipment can be classified as i) diver-assisted dredging tools, ii) surface-floating dredgers with deep-dredging capability and iii) submersible dredgers. Diver assisted dredging tools have limited capacity and involve human risk. Surface floating dredgers can work to a specific dredging depth controlled by their ladder length, but modification is limited by their large size and significant cost. Submersible dredgers are deployed for sub-sea operations and are the focus of this research. Submersible crawlers and walkers work in a submerged terrain-contact condition and depend on their apparent weight and ground reactions to counteract the excavation forces. Crawlers are inefficient in negotiating difficult sub-sea terrain and walking submersibles are slow moving over long-distances. Considering the constraints of dredging depth, negotiation of uneven terrain, slow motion, interchange ability of excavation or transport sub-system components and station keeping during operation, a new type of submersible dredger or miner was conceived. In working mode, it imitates a walking motion by spuds that are also used for station keeping during dredging. For longdistance travel, the vehicle can swim by means of vector thrusters. The vector thrusters also help in position-keeping and motion-control during swimming. To offset higher forces generated during excavation of hard materials, spuds, variable buoyancy tanks and control planes are included as secondary station-keeping devices. The paper describes the general arrangement and the distinguished sub-systems of the conceptualised vehicle. Special attention was given to working and swimming locomotion and the methods of station keeping during operation. Investigations about the station-keeping, propulsion and controlling conditions of the vehicle are in progress. Experiments to measure the cutting forces from the cutter design are described. It is expected that the new design will significantly contribute to the evolution of existing deep-dredging equipment with improved efficiency, increased mobility and location control while minimising larger environmental disturbances.