Work method of A cutter suction dredger

Cutter suction dredgers may:

• have a pontoon hull without a means of propulsion (non-propelled), or
• be self-propelled, sea-going specially designed vessels.

Whether self-propelled or not, the cutter will be moored with spuds or anchors while at work so that in essence the dredging operation takes place with the cutter in a stationary position.

Cutter head

The cutter suction dredger is equipped with a cutting device known as a cutter head. The cutter head is a mechanical rotating tool, which is able to cut hard soil or rock into fragments. It is mounted in front of the suction head and rotates along the axis of the suction pipe. This rotation disaggregates, i.e., separates, and excavates the soil which is then drawn into the suction pipe as a solid/water slurry and pumped to the surface.
Different cutter heads are designed for specific types of soil, because hard soil, non-cohesive or cohesive soils have different requirements. Dredging in hard soils will cause wear and tear so that cutter teeth need to be replaced regularly.

Spud pole

During operation the dredger moves around a spud pole by pulling and slacking on the two fore sideline wires. At the same time they cut with an accurate profile because of their movement around the spud. The spud stays in the same spot allowing the dredger to make concentric circles during swinging.

Transport of material

The material dredged by a cutter is usually transported hydraulically through a pipeline, although some cutters have barge-loading facilities as well.
The pumps produce the flow required to lift the disaggregated material from the bed and then to transport a water-soil slurry through a pipeline from the dredger to a discharge point. By use of booster pumps in the discharge lines, they can transport and place materials at considerable distances from the work site.

Advantages

The most powerful cutters can dredge hard rock effectively on a continuous basis. The self-propelled CSDs can travel long distances and be deployed in remote locations, far from their home port, making them flexible to be used all over the world. They can work in shallow waters and they also have flexible discharge alternatives.
Small and medium size cutter suction dredgers can be dismountable and transportable over land. The hull is then comprised of a series of pontoons, with the one pontoon containing the machinery.

Types of material

Cutters are powerful and are capable of dredging all kinds of material including hard rock. They are able to effectively dredge:

• silts,
• clays,
• sand,
• gravel,
• cobbles,
• fractured rocks
• and sound (unfractured) rocks.

Limitations

Cutter suction dredges are sensitive to rough seas and are not easily moved whilst working.

Production rates

Cutter suction dredgers characteristically have high production rates and the ability to effectively handle a wide range of materials. The production capacity designed is, of course, directly related to the hardness of the material that the cutter is going to dredge.

Project applications

Cutter suction dredgers are used wherever the seabed is hard rock. They are used for larger dredging projects such as navigation channels and port development and maintenance and land reclamation and in major projects such as the Panama Canal and the Suez Canal.