Trenching tool could eliminate normal pre-sweep operations

Successful trials have been performed off the Belgian coast with a new type of trenching method called flow dredging. For these tests, the hopper suction dredger Antigoon was directed towards a point near Zeebrugge. There the vessel was deployed in an entirely new way. Instead of pumping up the sediments and storing them in the dredger's hopper, the pumps were used to generate a water jet powerful enough to cut a deep trench in sand as well as clay. The hoppers remained empty as the

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The Flowdredger's flowhead is equipped with two main jets that distribute the dredged material evenly on each side of the trench. A 2 meter deep, 10-15 meter wide trench can be achieved at the system's first pass.


Successful trials have been performed off the Belgian coast with a new type of trenching method called flow dredging.

For these tests, the hopper suction dredger Antigoon was directed towards a point near Zeebrugge. There the vessel was deployed in an entirely new way. Instead of pumping up the sediments and storing them in the dredger's hopper, the pumps were used to generate a water jet powerful enough to cut a deep trench in sand as well as clay. The hoppers remained empty as the material was dumped on both sides of the trench.

Engineering for the Flowdredger was performed by Dredging International's Dutch subsidiary Tideway. A jet flowhead was developed and refined over an 18-month R&D program. The patented design comprises a combination of fine nozzles and twin main jets at each side of the head. These distribute the material evenly beyond each side of the trench.

"At pressures of 10 bar, we can achieve a 2-meter deep trench in sand at first pass," explains Flowdredger project engineer Bart Verboomen. "Even in clay we can produce a 1.5- meter deep trench during the initial pass. The jet digging force is much greater than from conventional systems." According to Verboomen, a bottom width of 10-15 meters can be achieved with ease. Pressures greater than 10 bar may be obtained by uprating the pumping capacity.

Dredging International states that the Flowdredger was developed to overcome the problem of material being scattered in all directions during operations with propeller-driven systems. A large amount of the dredged material normally returns into the trench.

The new system, however, is said to produce a clean and deep trench which could thereby eliminate the need for conventional offshore pre-sweep operations. The Flowdredger has already been used for wreck removal in the harbor of Antwerp.

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