A dredgers is a piece of equipment which can dig, transport and dump a certain amount of under water laying soil in a certain time.
The quantity of soil moved per unit of time is called Production.
Dredgers can dig hydraulically or mechanically.
Hydraulic digging make use of the erosive working of a water flow. For instance, a water flow generated by a dredge pump is lead via suction mouth over a sand bed. The flow will erode the sand bed and forms a sand-water mixture before it enters the suction pipe. Hydraulic digging is mostly done with special water jets. Hydraulic digging is mostly done in cohesionless soils such as silt, sand and gravel.
Mechanical digging by knives, teeth or cutting edges of dredging equipment is apply to cohesive soils.
The transport of the dredged soil can be done hydraulically or mechanically too, ether continuously or discontinuously.
Deposition of soil can be done in simple ways by opening the grab, turning the bucket or opening the bottom doors in a ship. Hydraulic deposition happens when the mixture is flowing over the reclamation area. The sand will settle while the water flows back to sea or river.
Dredging equipment can have these three functions integrated or separated.
The choice of the dredger for executing a dredging operation depends not only on the above mentioned functions but also from other conditions such as the accessibility to the site, weather and wave conditions, anchoring conditions, required accuracy and so on.
WS Dredge System Dredgers
200A Pump Dredger 450HP
250A Pump Dredger 530HP
300A Pump Dredger 850HP
450A Cutter Suction Dredger 2300HP
Cutter Suction Dredger 4000HP
Cutter Suction Dredgers
A plain suction dredger is a stationary dredger that position on one ore more wires, with at least one dredge pump, which is connected to the suction pipe and the delivery pipe. The suction pipe is situated in a well in front of the pontoon.
Good production can only achieved by this kind of dredgers either the soil is free running sand or the cut or breach height is sufficient (at least 10 m)
The discharge of the soil sucked is done either by pipeline or by barges.
Most suction dredgers are equipped with jet water pump(s) to assist either the beaching process or to improve the mixture forming process near the suction mouth.
The cutter suction dredger is a stationary dredger equipped with a cutter device (cutter head) which excavate the soil before it is sucked up by the flow of the dredge pump(s).
During operation the dredger moves around a spud pole by pulling and slacking on the two fore sideline wires. This type of dredger is capable to dredge all kind of material and is accurate due to their movement around the spud. The spoil is mostly hydraulically transported via pipeline, but some dredgers do have barge-loading facilities as well.
Sea going cutter suction dredgers have their own propulsion, however this is only used during (de) mobilization.
Cutter power ranges from 50 kW up to 5000 kW, depending on the type of soil to be cut.
The grab dredger is the most common used dredger in the world, especially in North America and the Far East.
It is a rather simple and easy to understand stationary dredger with and without propulsion. In the latter the ship has a hold (hopper) in which it can store the dredge material, otherwise the material is transported by barges. The dredgers can be moored by anchors or by poles (spuds)
The capacity of a grab dredger is expressed in the volume of the grab. Grab sizes varies between less than 1 m3 up to 200 m3.
The opening of the grab is controlled by the closing and hoisting wire or by hydraulic cylinders.
Dredgers with hydraulic cranes are available in two models: the backhoe and the front shovel. The first is used most. The difference between those two is the working method. The backhoe pulls the bucket to the dredger, while the front shovel pushes.
These stationary dredgers are anchored by three spud poles; two fixes to the front side of the pontoon and one movable at the aft side. This means that the dredging depth is limited to about 15 m. (maximum 25 m). At the front of the pontoon is normally a standard cranes mounted. Here pontoon deck is lower to increase the dredging depth. Bucket sizes vary from a few m3 to 20 m3.
Cutter Suction Dredger
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