Dredgers can excavate hydraulically or mechanically. The main difference between the two is mainly the transfer media. There are both advantages and disadvantages, the deciding factors varies from site to site. Recent project tends to favour the hydraulic method due to the better design and improved reliability of hydraulic systems.

The principal feature of all dredgers in this category is that the loosened material is raised from its in-situ state in suspension through a pipe system connected to a centrifugal pump. Various means can be employed to achieve the initial loosening of the material. Hydraulic dredging is most efficient when working with fine materials, because they can easily be held in suspension. Coarser materials – and even gravel – can be worked but with a greater demand on pump power and with greater wear on pumps and pipes. This method continuously pumps dredged material to a settling area, usually near or at the final disposal location.

Mechanical digging by knives, teeth or cutting edges of dredging equipment is use for cohesive material. Deposition of soil can be done in simple ways; by opening the grab, turning the bucket or opening the bottom doors in a ship.

Dredging equipment can have these 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.

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