Although systems for describing dredgers vary, in general three broad classifications are recognized based on the means of excavation and operation. These are known as mechanical dredgers, hydraulic dredgers and hydrodynamic dredgers.
Hydraulic dredgers include all dredging equipment which makes use of centrifugal pumps for at least part of the transport process of moving the dredged materials, either by raising material out of the water or horizontally transporting material to another site. Cutter suction dredgers (CSDs) are classified as hydraulic dredgers and are the most common vessels in the hydraulic/mechanical category. CSDs have the ability to dredge nearly all kinds of soils (sand, clay, rock) and are used where the ground is too hard for trailing suction hopper dredgers.
There are two types of cutter suction dredgers:
- CSDs which have a pontoon hull without the means of propulsion (non-propelled), and
- self-propelled CSDs that are shaped like a ship and are seagoing.
Although non-propelled CSDs are more common, even with self-propelled CSDs, the dredging operation takes place with the CSD in a stationary position, that is, even a self-propelled CSD will be moored with spuds or anchors while at work.