The Art of Dredging

Dredging and shipping

Backhoe dredger "POSTNIK YAKOVLEV":                         some serious earthmoving equipment.

 

Last year,  "POSTNIK YAKOVLEV" was launched on a Chinese yard.

This vessel is a self-propelled backhoe dredger, from a series of three identical vessels for "Jan De Nul", the two other named "Vitruvius" and "Mimar Sinan".

The vessel consist of a pontoon with twin azimuth propulsion thrusters, each 500 kW.

While in excavating mode, the pontoon is positioned by three spuds, hoisted with steelwires and winches. The crane is a  "Backacter type 1100" hydraulic crane, and comes with a range of buckets up to 40 m3 volume.

The choice of buckets and chisels or pickpoints depends on depending on soil conditions.

 

In the past dipper dredges have often been designed with machinery originally designed for work in a terrestrial environment. However, in designing Jan de Nul's Backacter 1100,  Shipyard De Donge in The Netherlands designed and built a powerful machine suited to the marine environment.

An important feature of the design of this crane is the placement of the hydraulic pump and machinery in the vessel’s hull; unlike previous marine backhoe models.

In addition to keeping the engines away from salt water, the fuel tanks are also located in the barge’s hull.

Backhoes of this size typically work in a spread with one or more barges in the 2000 m3 range. Barges are mostly split hoppers, making it easy to dump sticky material.

 

Main data

 

Length overall 69 m

Breadth 18 m

Draught 3,35m

Dredging depths up to 32 m

Buckets: 15m3 / 25 m3 / 40m3

Total installed power 3700 kW

Theoretical production at 20 m waterdepth: 800 m3/h, 

 

25 m3 bucket, not yet the largest in the crane´s arsenal

Equipped with some serious dents for heavy duty dredging... This thing can tackle rock.

Backacter type 1100 in action

Backhoes of this size can work in waves up to 1,5 meter. 

 

Outlook

 

In January 2009, the "Goliath" of Van Oord (an almost identical unit as "Postnik Yakovlev") almost sunk in the English Channel, while under tow. The "Goliath" had to be beached on the Kent coast to prevent it from sinking. (Read the story here)

The small propulsion package of this type has proven to be on the light side on a few occasions; it is strictly built for positioning in the dredge area. 

 

The general trend in scaling up hoppers and cutters can be noticed also in backhoes, exploiting economies of scale to the fullest.

Size matters.

 

 

 

The future might bring even larger units, built on a seagoing hull; with a more powerfull propulsion, and under unrestricted navigation class.

Swell compensation on the spuds may extend their environmental envelope even further.

 

Backhoes have come a long way since the pioneering years.

 

 

 

Marc Van de Velde

February 2010

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