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Types of dredger

Hydraulic Dredger
The principal function of all dredgers in this category is that the loosened material is raised from its in-situ state in suspension via a pipe system linked to a centrifugal pump. Varied means may be employed to achieve the initial loosening of the material. If it is naturally very loose, suction alone may be ample, however firmer materials might require mechanical loosening or the use of water jets. Hydraulic dredging is most efficient when working with fine supplies, because they will simply be held in suspension. Coarser materials – and even gravel – might be worked but with a larger demand on pump power and with greater wear on pumps and pipes.

A Suction Dredger is a stationary dredger used to mine for sand. The suction pipe is pushed vertically right into a sand deposit. If obligatory water jets assist to carry the sand up. It’s loaded into barges or pumped via pipeline directly to the reclamation area.

Profile or Plain Suction Dredger
In its most straightforward type the Profile or Plain Suction Dredger consists of a pontoon able to assist a pump and suction pipe and to make the connection to the offloading pipe. More sophisticated vessels have separate suction and delivery pumps, water jets on the suction inlet and articulated suction pipes. While working, a dredger could also be held in position by one or more spuds or, in deeper water, by a fancy system of moorings. Plain suction dredgers are mainly used to win fill materials for reclamation, with the material being positioned ashore by a floating pipeline. Very long distances might be pumped by the addition of booster pumps within the line. Materials could alternatively be loaded directly into barges moored alongsideside. The normal measures of dimension are the diameter of the offloading pipe, which can fluctuate between one hundred and 1,000 mm, or the installed horsepower.
Another use of plain suction dredgers – widespread within the USA – is to dredge from the navigation channel of a river and side forged the fabric to nearer the bank by way of a brief pipeline or simply by jetting. In this position they’re more commonly known as dust-pan dredgers.
Modern suction dredgers can recover material from great depths and may extract sand from below a clay overburden. Known as a deep suction dredger, this type offers the potential to recover fill materials from depths as much as one hundred m. Production is very dependent upon the permeability of the material dredged and is greatest in clean sands.

A Cutter Suction Dredger is a stationary dredger which makes use of a cutter head to loosen the fabric to be dredged. It pumps the dredged materials via a pipeline ashore or into barges. While dredging the cutter head describes arcs and is swung across the spud-pole powered by winches. The cutter head will be changed by several kinds of suction heads for special functions, similar to environmental dredging.
When the in-situ materials is just too compact to be removed by suction action alone, some form of mechanical loosening should be incorporated near the suction mouth. The most typical method is a rotating cutter: the main characteristic of the cutter suction dredger. This is mounted on the decrease finish of the ladder used to help the cutter drive and the suction pipe. The loosened materials then enters the suction mouth, passes by the suction pipe and pump (or pumps) and into the delivery line.
Cutter suction dredgers operate by swinging about a central working spud using moorings leading from the decrease end of the ladder to anchors. By pulling on alternate sides the dredger clears an arc of reduce, after which moves forward by pushing against the working spud using a spud carriage. A usually smooth bottom can be achieved, and modern instrumentation permits profiles and side slopes to be dredged accurately. A few of the larger cutter suction dredgers are self-propelled to permit simple movement from site to site.
The dimensions of a cutter suction dredger is measured by the diameter of the suction pipe and by the put in machinery power. Pipe diameters are within the range 100 to 1,500 mm. A contemporary highly automated cutter suction dredger is capable of achieving high outputs over sustained intervals and production rates of around 500,000 m³/week are attainable under good conditions.
Cutter suction dredgers can be used to deliver by way of a pipe- line or to load barges. They may even be used simply as loosening units for materials to be re-handled by one other type of dredger, in which mode offloading is directly over the stern to the sea. Pipeline offloading is most typical but is vulnerable to waves and currents and causes an obstruction to different vessels. To keep away from these problems part of the pipeline may be submerged and laid on the channel-or sea-bed.
Cutter suction dredgers are primarily used for capital dredging, particularly when reclamation is related with the dredging. Smaller vessels can be dismantled into sections and moved by road or rail for work in inland waterways, sludge lagoons, reservoirs and related isolated areas. Giant heavy-duty cutter dredgers are capable of dredging some types of rock which have not been pre-treated.
An alternative form of loosening is the use of a rotating bucket wheel at the suction mouth. Bucket wheel dredgers are most commonly utilized in mineral extraction operations and so far haven’t discovered basic favour among the main international dredging contractors.

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What is a Dredge Cutter?

A cutter refers to the type of excavator head equivalent to a basket cutterhead or bucketwheel on a hydraulic pipeline dredge. The cutter houses the suction intake and is used for reducing or agitating the supplies which might be being dredged.

Cutters have fundamental features:

Loosen and break up materials from the bottom of a waterway into smaller fragments that are appropriate with the dredge’s pumping system.
Intro the crumbled particles into the high-velocity stream at the suction intake in a prescribed capacity the place the materials will be then pumped and transported via a dredge’s hydraulic pipeline system.

Specialised types of dredger are often of small dimension and output. They embrace simple jet-lift and air-lift, auger suction, pneumatic and amphibious dredgers.
Jet-lift dredgers use the Venturi effect of a concentrated high-speed stream of water to draw the adjacent water, together with bed material, right into a delivery pipe. The jet head has no moving parts so blockage by wires and other dock debris is minimised. These dredgers are relatively small units and a few can be manoeuvred on spuds alone.
Air-lift dredgers are very similar to the jet-lift dredgers however the medium for inducing water and material flow is high pressure air injected on the mouth of the suction pipe. As with jet-lift dredgers there are no moving parts in the flow system. Hard or other troublesome to loosen materials cannot be dredged.
Augur suction dredgers operate on the identical principles as a cutter suction dredger, besides that the mechanical chopping tool is a rotating Archimedean screw placed at right angles to the suction pipe. The screw dislodges materials, which is fed to the centrally placed suction pipe. Most units have a shroud over the reducing screw which reduces the spread of the plume of disturbed bed material which normally escapes from all dredgers. The augur suction dredger advances into the reducing face by hauling itself along a wire deployed directly ahead. Very accurate horizontal and vertical dimensions can be achieved.
Pneumatic dredgers work on the ‘evacuator’ principle. A chamber with inlets for bed material is pumped out with the inlets closed. The inlets are then opened and water and materials drawn in. The mixture is then pumped out and the cycle repeated. The unit is generally suspended from a crane on land or from a small pontoon or barge. The dredging action is intermittent and suitable only for easily flowing material.
Amphibious dredgers have the unusual feature of being able to work afloat or elevated clear of the water surface on legs. They can be outfitted with grabs, buckets or a shovel installation.
All the above specialist types of dredger (and others) have been developed for particular situations and usually for small scale work reminiscent of narrow canals, industrial lagoons and reservoirs. Some types have been developed to handle contaminated sediments with minimal disturbance. They aren’t usually employed for large scale maintenance or capital dredging work.
An additional type of dredger is the plough or bed leveller. This consists of a blade or bar which is pulled behind a suitable tug or work-boat. The strategy can be used for direct dredging over brief distances and for levelling off the bed to the desired depth when a trailer or seize dredger is operating. It might even be used to tug away material located near quay walls and other places the place a trailer cannot attain right into a more accessible area. Typically the trailer itself operates the leveller if no tug or work-boat is available.

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