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The former DDR issued in 1981 a set of stamps which shows different vessels used on their inland waterways.
The inland waterways of the former DDR have a length of around 2.500km. To maintain these waterways and keep her open for the inland vessels they use “bucket-ladder dredgers” one of this is depict on the 85pf. Stamp.

Bucket-ladder dredgers are one of the oldest types of dredger. They usually comprise of 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, by rotating the bucket chain over tumblers wheels on both ends, the buckets which scraps and scoops up from the bottom of the canal the dirt and mud and when it is at the top of the ladder she discharged her material in the drop chutes and into a barge moored alongside the dredger.

Some of the bucket-ladder dredges are self propelled but most are positioned in place by anchors, and moved while dredging along semi-arcs by winches.

The depicted bucket-ladder dredger was put in service in 1970, and the capacity of one bucket was 630 litres.

More info on a bucket-ladder dredger is given in http://www.european-dredging.info/ab6.html .

East Germany 1981 85p sg E2422, scott?

Source: the mentioned URL and Navicula.

Austria issued in 1992 one stamp for the 100th years Rhine River regulation treaty between Switzerland and Austria.
1892 A treaty was signed between the Governments of Austria and Switserland on the regulation of the expenses between the two countries to keep the River Rhine navigable
The stamp shows a bucket ladder dredger used in the River Rhine to keep the River Rhine navigable.

A bucket dredger is a tool in the dredging industry that, using a bucket ladder with bucket chain, which dredge sand and sludge with the aid of dredge buckets from the bottom. These buckets are rotated around the ladder and therefore cut very accurately the ground.

History
The bucket dredger is one of the oldest tools in hydraulic engineering which was initially driven by muscle power of humans or animals. In 1750 the first ladder dredger was built with iron buckets in France . In 1796 the first steam buckut ladder dredger was built, designed by James Watt , and in the 20th century diesel engines were used. In the 1870s, trailing suction hopper dredgers came into use and these replaced the bucket dredgers . Nowadays worldwide only a few bucket dredgers are in operation.

Operation
The dredger itself is actually mounted on a steel container or pontoon . From the prow to about the middle in the bin in the longitudinal axis, an incision (called bun or beun) has been applied. In the middle of the vessel is the main gantry, a steel constructed gantry, on which the bucket ladder rests. This bucket ladder is suspended at the bottom from the ladder gantry, which is positioned close to the bow of the vessel. In the ladder stand there is a lifting mechanism that lowers the ladder bucket to the desired depth to dig the ground.

When moving the bucket dredger, the ladder bucket is largely lifted out of the water.
The bucket ladder serves to guide the bucket chain. This is an endless chain with long links on which the buckets are attached. The bucket chain runs at the upper end of the ladder over a pentagonal drum, the so-called five-sided, and at the bottom over the so-called hexagon, and further over rolls, which are attached to the bucket ladder. The number of buckets is 30 to 40 pieces and the content depends on the capacity of the dredger. The capacity of a bucket is between 300 and 850 liters. The buckets have interchangeable edges of hardened steel along the top to scrape the soil from the river or seabed. In the bottom of each bucket there are one or more holes, in order to let the water that is in the bucket drain away as much as possible during collection.
The full buckets are brought up and the contents are collected in a cistern every times when tilting. The two discharging chutes connected there will transport the dredged soil into a barge next to the dredger. If a chute is not in use, the bottom part can be brought into a perpendicular position, so that the gutter does not protrude outside the vessel. A movable flap is fitted in the cistern, making it possible to use the left or the right chute.

There are bucket dredgers with and without propulsion. In the latter case, a tugboat must move the dredger to a new project. The bucket dredger moves at the dredging site by means of winches. On the deck of the dredger winches are placed in front, behind and on the sides. The cables of the winches are connected to anchors or fixed points on the land. The winches on the sides bring the dredger from side to side of the river or channel. The winch is then tightened to the bow anchor and the rear wire is lifted, with which the dredger moves forward. Subsequently, the winches are used again to dredge away a next strip.

In 1953, for that time, the largest and most modern bucket dredger in the world was delivered. This, diesel electric, dredger (FRIESLAND) was commissioned by the owner, R. Boltje & Zonen NV from Zwolle, Netherlands equipped with superstructures for the crew. The vessel was also equipped with a 4-meter long anchor wire guide posts, so that a bottom unloading unit could easily pass alongside the dredger without touching the anchor wires. These modifications were later applied as standard to dredgers in the Netherlands and abroad.
The bucket ladder dredger is mainly used for deepening waterways and ports. Furthermore, she are used by excavating dams and dikes.

Source: https://nl.wikipedia.org/wiki/Emmerbaggermolen
Austria 1992 7s sg2297, scott 1570 ( the vessel alongside is a barge)