A cutter refers back to the type of excavator head reminiscent of a basket cutterhead or bucketwheel on a hydraulic pipeline dredge. The cutter houses the suction intake and is used for chopping or agitating the supplies which can be being dredged.
Cutters have two basic capabilities:
Loosen and break up supplies from the underside of a waterway into smaller fragments which can be appropriate with the dredge’s pumping system.
Intro the crumbled debris into the high-velocity stream at the suction intake in a prescribed capacity where the supplies can be then pumped and transported through a dredge’s hydraulic pipeline system.
Specialised types of dredger are normally of small measurement and output. They include 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, collectively with bed material, right into a delivery pipe. The jet head has no moving parts so blockage by wires and different dock debris is minimised. These dredgers are relatively small units and a few may be manoeuvred on spuds alone.
Air-lift dredgers are 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 different troublesome to loosen materials can’t be dredged.
Augur suction dredgers operate on the same principles as a cutter suction dredger, except that the mechanical chopping instrument is a rotating Archimedean screw placed at proper angles to the suction pipe. The screw dislodges material, which is fed to the centrally positioned suction pipe. Most units have a shroud over the slicing screw which reduces the spread of the plume of disturbed bed materials which usually escapes from all dredgers. The augur suction dredger advances into the reducing face by hauling itself alongside a wire deployed directly ahead. Very accurate horizontal and vertical dimensions might 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 combination 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 motion is intermittent and suitable only for simply flowing material.
Amphibious dredgers have the weird characteristic of being able to work afloat or elevated clear of the water surface on legs. They can be geared up with grabs, buckets or a shovel installation.
All of the above specialist types of dredger (and others) have been developed for particular situations and usually for small scale work reminiscent of slim canals, industrial lagoons and reservoirs. Some types have been developed to handle contaminated sediments with minimal disturbance. They don’t seem to be normally 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 short distances and for levelling off the bed to the desired depth when a trailer or grab dredger is operating. It could also be used to tug away materials positioned near quay partitions and different places where 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.