Cable reburial required ‘out of the box’ thinking

Jan De Nul was requested by Eneco to rebury a section of an existing export cable for the Luchterduinen offshore wind farm in The Netherlands as coastal erosion was bringing the cable closer to the surface.

Since the section of decreased burial depth was located in the nearshore zone, it was not accessible with typical offshore trenching vehicles nor could it be easily accessed from the beach. Jan De Nul offered Eneco the solution by mobilizing its intertidal trencher, Sunfish, which successfully lowered the nearshore part of the cable working up to 1 kilometre offshore and a water depth of 8.5 metres.

Ernest Diepstraten, Project Manager at Eneco: “Eneco greatly appreciated working together with Jan De Nul constructively in delivering this project in time and in budget. We are pleased that, thanks to the work of Jan De Nul Group, the cable to our Eneco Luchterduinen wind farm is buried deep enough again so that the wind farm can continue to supply power to our customers.”

Specifically for this project, the Sunfish was modified to a suitable post-lay jet-trenching vehicle with 2 water pumps delivering each 1250 m³/hr jet water and 3.5 m long jet swords.

The Sunfish was initially designed as a ploughing machine suitable for working in tidal areas. In this configuration, it successfully buried export cables on the Race Bank project in the UK in 2016. Jan De Nul engineers converted the machine later into an excavator with a chain cutter, a configuration which was used for the burial of the Rentel export cable in Belgium in 2017. Today, the Sunfish successfully completed the Eneco Luchterduinen export cable reburial in jetting configuration by using water under high pressure.

To accurately locate the cable, the Sunfish was further equipped with 2 sets of innovative cable tracker sensors of SMD’s innovative tracking system ‘Artemis’ using the live tone of the cable. As a result, Eneco did not have to switch off the wind farm during the entire campaign.