TSHD has several special features, the main one being a drag arm which works as vacuum cleaner. An equivalent arrangement is employed for the twin jet pumps on the port side. The single dredge pump is driven directly off the forward end of the starboard main engine through a clutch coupling, a long shaft and a two-stage variable-speed gearbox. The maximum power available for propulsion is 2000kW per propeller. Each engine drives through reduction gearbox 2500mm diameter CP propeller running at 230 rpm in the nozzle. The dredger is powered by two Wärtsilä 6元2 engines, each of 2760kW MCR output at 750rpm. Trailing suction hopper dredgers are used for maintenance work (removal of deposits in approach channels) and dredging of trenches in softer soils. At each side of the ship is a suction arm, which consists of a lower and a higher part, connected through cardanic joints. It is a shipshaped vessel with hopper type cargo holds to store the slurry. Trailing suction hopper dredger (TSHD) – The trailing suction hopper dredger is nonstationary dredger, which means that it is not anchored by wires or spud but it is dynamically positioned the dredger uses its propulsion equipment to proceed over the track. The dredged soil is discharged either by pipeline or by barges. Plain suction dredger – A plain suction dredger is a stationary dredger positioned on wires with at least one dredge pump connected to the suction pipe situated in a well in front of a pontoon. Grabs can manage both sludge and hard objects (blocks of stone, wrecks) and this makes them suitable for clearing up waters that are difficult to access (canals in cities), or for gravel winning and maintenance dredging on uneven beds.

Dredged material is loaded into barges that operate independently. Grab dredger – A grab dredger employs a grab mounted on cranes or crane beams. See also Cutter suction dredger d’ARTAGNAN.

Seagoing cutter suction dredgers have their own propulsion. These dredgers are often used to dredge trenches for pipe lines and approach channels in hard soil. During operation the cutter suction dredger moves around a spud pole by pulling and slacking on the two fore sideline wires. Cutter suction dredger – The cutter suction dredger is a stationary dredger equipped with a cutter head, which excavates the soil before it is sucked up by the flow of the dredge pump. Positioning and movements are achieved by means of winches and anchors. The buckets are inverted as they pass over the top tumbler, causing their contents to be discharged by gravity onto chutes which convey the spoil into barges alongside. The bucket chain dredger uses a continuous chain of buckets to scoop material from the bottom and raise it above water. These days, this classic vessel is mainly used on environmental dredging projects. Bucket dredgers are held in place by anchors. The buckets are attached to a chain and graded according to size (200 to 1000 litres). Bucket chain dredger – Bucket chain dredge or bucket ladder dredge is a stationary dredger equipped with an endless chain of buckets carried by the ladder. Its main advantage is its ability to dredge a wide range of materials, including debris and soft, weathered or fractured rocks. Backhoe dredger – A backhoe dredger is based on the giant land-based backhoe excavator that is mounted at one end of a spud-rigged pontoon. The dredged material which has been loosened from the sea-bed is sucked up and transported further as a mixture (solid material and water) using centrifugal pumps. Hydraulic excavating is done with special water jests in cohesionless soils such as silt, sand and gravel. The dredged material is excavated and removed using mechanical means such as grabs, buckets, cutter heads or scoops. Mechanical excavating is applied to cohesive soils. There are two methods of dredging: mechanical excavating and hydraulic excavating. Maintenance dredging is now only a basic task, while other fields are growing in demand much faster: creating new land for port and industrial development trenching, backfilling and protection work for offshore pipelines, coastal outfall pipelines and for cables laid on the sea bed environmental dredging and clean-up of contaminated sediments replenishment of beaches and coastlines, not only for coastal protection, but also for recreational uses. One of the applications meets the need to maintain minimum depths in canals and harbours by removing mud, sludge, gravel and rocks. Dredging is a displacement of soil, carried out under water.

Dredge definition