New Approach of Deep Sea Dredging

Abstract

A new approach of trailing suction dredging is presented. This approach is especially useful for dredging at depths over 100m. Normally a Jumbo Trailing Suction Hopper Dredger is used for dredging at depths of over 100m. This requires a large investment. The expensive dredging equipment is only used while dredging. This equipment is mainly “dead cargo” when sailing to the place of delivering the sand. Our new approach requires a significant lower investment. As the dredging equipment is used continuously, idle time is decreased and time for return of investment is shortened. The dredging depth is independent of the length of the trailing suction pipe and thus the length of the ship, unlike a normal Trailing Suction Hopper Dredger. Our approach consists of modular dredging equipment placed on e.g. a standard Platform Supply Vessel. By using the dredging equipment on this vessel, standard barges are continuously filled with sand. The dredging equipment consists of a submersible dredging unit connected to a hose. This dredging unit is suspended by wires from the Platform Supply Vessel. It is lowered to the required dredging depth by winches. The application of the dredging unit is like a normal Trailing Suction Hopper Dredger. The barges are loaded while sailing along the Platform Supply Vessel. The position of the dredging unit is constantly monitored. An extensive research project is initiated to develop this concept. Several scale model tests are performed at MARIN. Also a numerical model was designed. Extensive tests were performed on the hose. Another test was performed at TU Delft to investigate the transport of sand/water mixture through a hose stored on a reel. All this research has resulted in a reliable, inexpensive system to dredge at sea at great depths over 100m.