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Kriegers Flak BC Photo 4

Kriegers Flak (Denmark) – Boulder Clearance

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The Kriegers Flak BC (Boulder Clearance) project concerns the boulder removal operations at predefined footprints for the subsequent jack-up barge operations for the WTG installation at the Danish Kriegers Flak OWF.

This wind farm of 72 locations, developed, designed, built, and operated by Vattenfall, is located in the Baltic Sea area. Specifically, the DKF site is situated in the eastern part of Danish territorial waters and the Danish Exclusive Economic Zone, directly next to the maritime border with Germany and Sweden. The closest distance to the Danish coastline (island of Møn) ranges between ca. 13 km and 39 km.

The presence of surface boulders at the Danish Kriegers Flak site was widespread throughout. This would pose several potential hazards to jack up vessel operations and subsequently a boulder mitigation strategy was required.

Vattenfall had awarded Asso a contract for the execution of boulder clearance works. The scope of works was performed by TSV Aethra and MSV Astrea, as per the below split. 

Summary of TSV Aethra’s works:

  • 120 Plough Passes were executed to clear a total area of 16.606 m2 from boulders and boulder clusters.
  • 1230 Tine/Clamshell Grabs performed to remove individual Boulders and Spoil Heaps utilizing a boulder-grabbing ROV (AssoGrapple).
  • 3 large boulders (up to 17Te) were removed from the clearance area using a crane-operated Orange Peel Grab.
  • 30km of multibeam echosounder (MBES) and sidescan sonar (SSS) survey to verify the final state of the seabed.

Summary of MSV Astrea’s works:

  • Total targets removed 3,490 consisting of boulders and a few debris by chartered Tine Grab

Asso’s scope of work included:

  • Preparation Activities // Mobilization activities
  • Boulder removal
  • As-built (MBES/SSS) survey 


  • Owner
    Vattenfall Vindkraft Kriegers Flak P/S
  • Contractor
    Asso.subsea Ltd.
  • Year
  • Location
  • Cable Type
  • Max Water Depth


Some of the services we provided for Kriegers Flak (Denmark) – Boulder Clearance 

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  • Aethra

    DP II – Trenching Support Vessel The Aethra is a DP-2 Trenching Support Vessel built for worldwide operations, …

    Aethra Trenching Support Vessels
  • Astrea

    DP II – Multipurpose Support Vessel The Astrea is a DP-2 Multipurpose Support Vessel built for worldwide operations …

    Astrea General Support Vessels


  • AssoGrapple I

    The Assograpple I is a purpose-built construction able to remove rocks or similar products, it also incorporates a …

    AssoGrapple I Pre-Trenching/Boulder Clearance, Seabed Preparation Equipment
  • Multi-functional Plough

    The Multi-Functional Pre-Lay Plough represents the latest investment of ASSO Group in order to cover the constantly evolving …

    Multi-functional Plough Pre-Trenching/Boulder Clearance, Seabed Preparation Equipment

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