Cutter suction dredgers (CSDs) combine the two basic principles of dredging: excavation and suction. A rotating cutting tool dislodges the soil so that it can be drawn into a suction pipe. This type of dredger can handle all kinds of soil, from sand and gravel to heavily compacted and hard materials such as clay, soft rock and even thin layers of hard rock. Therefore, CSDs can be used for a wide range of dredging projects, including land reclamation, port construction and waterway maintenance, mining, reservoirs and hydropower lakes excavation and environmental dredging.
Main features of CSDs:
- combination of mechanical excavating and hydraulic dredging with centrifugal dredge pumps and a rotating cutterhead
- stationary dredger – large, custom-built CSDs can be self-propelled, but they do not sail whilst dredging
- accurate dredging system with good control on vertical and horizontal position
- suitable for almost any type of soil including soft rock and rock of moderate strength
- transport of dredged materials through pipelines
- dismountable and transportable over land
- allow for single-handed operations
- production of up to 6,000m3/hour.
How do CSDs work?
Whilst dredging, CSDs remain stationary by means of a spud that is lowered into the seabed. The dredger dredges by making a sideways swinging motion using anchors and winches. That way, very accurate dredging results can be achieved. The dredger moves forward by lowering the second spud – the so-called walking or auxiliary spud – for a short period, allowing the operator to reposition the working spud. Hence, CSDs are not designed to operate in swell conditions. The movements of the vessel may bend the spuds or damage the hinges of the ladder. Utilising central anchor systems (Christmas trees) instead of spuds can extend the workability in swell, but this affects the manoeuvrability and efficiency of the operation.
Initial investment costs of a cutter suction dredger
Standardised CSDs come in a range of different sizes and are often available from stock. The price for a turnkey standardised CSD starts at around €0.5 million, depending on its size and the installed power. They are easily customisable with a wide range of options such as additional dredge pumps, dredge wheels, a spud carriage system and automation systems, as well as auxiliary equipment, such as work boats and discharge pipelines.