Almost no turbidity with new-design cutter suction head
Picture caption: Dredge BV is expanding its range of cutter heads
Dredge Yard BV is developing a new type of cutter head to reduce spillage during cutting and pumping operations, without compromising performance. Spillage from operation of cutter suction dredgers could be as much as 80% according to some estimates, and these can cause increases in local water turbidity as a result. While this sediment will eventually resettle on the seabed, the plume is unsightly in the meantime and can lead to an unfavourable public response. There are also concerns that turbidity in the water column can have biological and chemical impacts on marine ecosystems in the meantime, particularly those which rely on light penetration for photosynthesis and other processes.
But the sheer volume of spilled material is an operational concern for dredging operators as well. Lost material, once it has settled, forms a soft sediment layer which extends the dredging operation, necessitating further passes once the initial cutting process is completed.
Rather than a using a conventional hemi-spheroid shape, audience members at the CEDA Dredging Days 2021 Conference heard, Dredge Yard’s new distinctive closed-type cutter head uses an Archimedean screw design with scooped edges. These aerofoils, as they are described, are designed to coax more of the cut material up into the suction tube before it slides off the blades.
In simulations, the new design cutter head showed incredible promise, with a flow rate of more than double that of a conventional cutter head; 0.069m3/s versus 0.032m3/s for a conventional cutter head.
This, too, was borne out in later physical tests. Researchers dry-tested a full-sized version of the cutting head, and discovered that the spill layer – the layer of spoil left on the dredged area, necessitating further cleaning to allow full depth to be achieved – was less than half that with a conventional cutter head, implying that the total spillage from the operation had been more than halved versus the conventional cutter head.
“Because we have a low turbidity, we were able to make a nice video underwater,” joked Basel Yousef, Dredge Yard CEO, to audiences as he exhibited the cutter head in action. “After the dredging, the survey shows a very even cut from the new cutter head, and more variation on the older cutter head. With the new cutter head, we had less vibration on board, and power consumption was low.
“Using this cutter head, there is no need for a ‘cleaning cut’, turbidity is almost non-existent below 40 RPM. Using this cutter head allows the dredger to offer environmental [friendly] dredging.”
The presentations and discussion from CEDA Dredging Days 2021 conference can be watched on-demand by registered participants until the end of the year on the conference’s platform: https://www.cedaconferences.org/dredgingdays2021. After event registration is open for on-demand access.