Envirotech ENGINEERING Lda is a dredger supplier for contractors
We supply new and used dredgers in good condition;
Plus other equipment needed for your dredging job, such as booster pumping modules, piping, buoyant devices, etc.
From suction cutter dredgers of 6" to 24" or bigger, to dredging barges, we can supply it at the best price, complete with training for your staff at job start-up.
TYPES OF DREDGERS BY SUCTION
These operate by sucking through a long tube, like some vacuum cleaners. A plain suction dredger has no tool at the end of the suction pipe to disturb the material. This is often the most commonly used form of dredging.
Trailing suction
A trailing suction hopper dredger (TSHD) trails its suction pipe when working, and loads the dredge spoil into one or more hoppers in the vessel. When the hoppers are full the TSHD sails to a disposal area and either dumps the material through doors in the hull or pumps the material out of the hoppers. Some dredges also self-offload using drag buckets and conveyors. The largest trailing suction hopper dredger in the world is currently Vasco da Gama (Jan De Nul) with its 33,000 cu.m. hopper and a maximum dredging depth of 135m. The next mega trailing suction hopper dredgers Cristovao Colombo and Leiv Eriksson are actually under construction in Spain and should be delivered in 2008. Main design specs are the 46,000 cu.m. hopper and a design dredging depth of 155m.
Cutter suction
A cutter-suction dredger's (CSD) suction tube has a cutter head at the suction inlet, to loosen the earth and transport it to the suction mouth. The cutter can also be used for hard surface materials like gravel or rock. The dredged soil is usually sucked up by a wear resistant centrifugal pump and discharged through a pipe line or to a barge. In recent years dredgers with more powerful cutters have been built in order to excavate harder and harder rock without blasting.
Auger suction
This process functions like a cutter suction dredger, but the cutting tool is a rotating Archimedean screw set at right angles to the suction pipe. The first widely used auger dredges were designed by Mud Cat in the 1980s.
Jet-lift
This uses the Venturi effect of a concentrated high-speed stream of water to pull the nearby water, together with bed material, into a pipe.
Air-lift
An airlift is a type of small suction dredge. It is sometimes used like other dredges. At other times, often an airlift is used handheld underwater by a diver. It works by blowing air into the pipe, and dragging water with it.
Bucket
A bucket dredger is a dredger equipped with a bucket dredge, which is a device that picks up sediment by mechanical means, often with many circulating buckets attached to a wheel or chain. Some bucket dredgers and grab dredgers are powerful enough to work through coral reefs to make a shipping channel.
Grab
A grab dredger picks up seabed material with a clam shell grab, which hangs from an onboard crane, or is carried by a hydraulic arm, or is mounted like on a dragline. This technique is often used in excavation of bay mud. Most of these dredges are crane barges with spuds.
Backhoe/dipper
A backhoe/dipper dredge has a backhoe like on some excavators. A crude but usable backhoe dredger can be made by mounting a land-type backhoe excavator on a pontoon. The two largest backhoe dredgers in the world were Tauracavor (Great Lakes), New York (Great Lakes) and Il Principe (Jan De Nul). Both feature a barge mounted excavator. In 2007, the new generation of backhoe dredgers has arrived. The typified backhoe dredges of these days are a new and revolutionary designed type of dredging excavator mounted on a pontoon with enhanced capabilities in respect of penetration force, production and maintenance.
Water injection
A water injection dredger injects water in a small jet under low pressure (low pressure because the sediment should not explode into the surrounding waters, rather it is carefully moved to another location) into the seabed to bring the sediment in suspension, which then becomes a turbidity current, which flows away down slope, is moved by a second burst of water from the WID or is carried away in natural currents. Opposition claims that Water Injection Dredging is not a natural way of dredging while the side of the WID claims otherwise.
As a side note: Water injection results in a lot of sediment in the water which makes measurement with most hydrographic equipment (for instance: single beam echo sounder) difficult and should make use of filtering to produce better results.
Pneumatic
These dredgers use a chamber with inlets, out of which the water is pumped with the inlets closed. It is usually suspended from a crane on land or from a small pontoon or barge. Its effectiveness depends on depth pressure.
Bed leveler
This is a bar or blade which is pulled over the seabed behind any suitable ship or boat. It has an effect similar to that of a bulldozer on land.
