Cutter Suction Dredgers (CSD)
There are at present only 8 self propelled 'Cutter Suction Dredgers' in operation worldwide.
These dredgers are large high powered vessels used for 'cutting' the sea bed.
Most CSDs are barges that are towed to the required areas and are anchored or spudded to the sea bed. Spuds are used, since the loads on the cutter at nozzle length are high and the spuds keep the vessel from moving whilst dredging. These spuds are heavy pike-like structures which can be dropped into the sea bed by the dredger.
See below for a video animation of Cutter suction dredger (CSD) Beaver B50 in action, swinging and changing spuds.
Cutter suction dredgers are used to deepen harbour berths or channels and areas where the sea bed is harder than normal and where a suction dredger cannot lift the required spoil. The dredger literally cuts the hard materials and rock away from the sea bed and sucks it through the cutter suction pipe. This is then discharged ashore or to barges for spoil removal.
The suction tube has at its end a hydraulically operated cutting wheel that cuts the hard sea bed into small chunks of rock and spoil. The size of the associated cutters depends on the hardness factor of the sea bed. The cutter units have a high pressure nozzle at their centre and this is used to agitate the cut spoil. The spoil is then normally lifted using an ejector system from the main pump through the suction pipe, so the hard spoil does not go through the moving parts of the pumps.
The spoil is seldom retained on the CSD vessel, but is normally pumped by the ejector system directly ashore or into hopper barges or large lighters, for removal from the site. This can be up to 5,000 metres distance on the most powerful of vessels.
See below for a video animation of Cutter suction dredger (CSD) IHC 8527 MP in action.