Hollandse Kust Offshore Windfarm

Case Study Overview

Jan De Nul Group contracted Red7Marine to supply its 400t Haven SeaSeven Jack-Up vessel for the export cable installation at Hollandse Kust offshore windfarm.

As a part of the project, Red7Marine was responsible for the design and fabrication of a cable highway platform for the vessel to support 8T/m2 loadings and 20T of lateral forces for cable tensioning operations.

At a glance

  • Location: Hollandse Kust Offshore Windfarm, Netherlands
  • Plant used: 400T Haven SeaSeven
  • What we did: Red7Marine designed and fabricated a bespoke cantilever platform for Jan De Nul to support cable tensioning operations at Hollandse Kust Offshore windfarm.
hollandse kust


The cable highway platform concepts were developed over a five-month period. Conceptual drawings were produced with the final dimensions of the cantilever platform agreed at 2.5m x 31.5m (length of the vessel).

Red7Marine’s coded welders fabricated the platform within the company’s quayside fabrication and maintenance workshop on the banks of River Orwell in Ipswich.

hollandse kust challenge


The SeaSeven was mobilised in Tilbury where the cantilever cable highway system was installed on the barge before its departure to the Netherlands. The mobilisation included:

  • Relocating refurbished bollards and fairleads
  • Installing 6 x platform cantilever brackets and 3 x platform top
  • Installing handrails to the perimeter of the platform
  • Installation of the CTV ladder
hollandse kust solution


Following its arrival in the Port of Ijmuiden, the barge was situated on-site in the nearshore intertidal area. The platform cantilevered 2.4m over the portside of the barge and was used during the export cable installation to act as a tensioner station to reduce the total export cable tension.

hollandse kust solution



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“Our relationship with Red7Marine and their Personnel through all stages of this challenging Project has been based on partnership and co-operation. A huge consideration was given at the initial phase to identify potential difficulties. This has been followed by development of various scenarios and methods of addressing such difficulties which provided a great benefit during actual works. We look forward to continuing the relationship with the Red7Marine team.”

Kate Sellers, Site Agent BAM Nuttall