A Bucket Dredger is a stationary dredger, fixed on anchors and moved while dredging along semi-arcs by winches. The bucket dredger is one of the oldest types of dredging equipment. It has an endless chain of buckets that fill while scraping over the bottom. The buckets are turned upside down and empty moving over the tumbler at the top. The dredged material is loaded in barges.
Bucket ladder dredges usually comprise a rectangular pontoon with a central well in which a heavy steel frame or ladder is suspended. The ladder supports an endless chain of buckets, each of which is equipped with a cutting edge. By rotating the bucket chain about flat-sided wheels (known as tumblers) at each end of the ladder, material can be loosened and transported. A small proportion of the dredgers of this type are self-propelled. The propulsion machinery is used to move the vessel from site to site, but is not used in the extraction operation.
The dredging action starts when a bucket reaches the bottom of the ladder, where it loosens and scoops up a quantity of material. This material is carried in the bucket to the top of the ladder where, at the highest point of the chain, the bucket overturns and the contents are offloaded. The material falls into drop chutes and into a barge moored alongside the dredger. Each bucket then returns empty on the underside of the chain to the bottom of the ladder where the cycle begins again. The size of a bucket dredger is usually described by the capacity of the buckets, which is in the range 100-900 litres.
Bucket ladder dredgers are able to dredge almost any material up to the point where blasting is required, and if fitted with ripper teeth may even be directly able to dredge weak rock. A minimal amount of water is added to the dredged material during careful use of the buckets. This is advantageous to production and costs, especially when dredging in silt and mud.
In operation, a bucket ladder dredger is held accurately in position by up to six moorings or anchors and the bucket ladder moved from side to side to excavate material. On average our bucket dredgers can achieve a 800m3 capacity of sand per hour using a conveyor belt system to transfer on to self propelled self discharge hopper barge.