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January - Repair of Sub-sea Cable near Bornholm

In January a part of the subsea power cable between Bornholm and Sweden was damaged due to the dragging of a ship’s anchor along the seabed.

Date: January/February 2010

Client: Energinet.dk

In January a part of the sub-sea power cable between Bornholm and Sweden was damaged due to the dragging of a ship’s anchor along the seabed. On discovery of the fault, Energinet.dk contacted JD-Contractor A/S; and C/S Cable One was immediately sent to the area. The main tasks for JD-Contractor A/S were:

  1. Localisation of the anchor trace on the seabed
  2. Assess the location and extent of damage to the cable
  3. Removal of the damaged cable
  4. Laying of spare cable
  5. Splicing of spare cable segment to remaining cable at joints 33 and 34

All large vessels are required to have Automated Identification System (AIS) installed, which continuously transmits a VHF signal containing information including the vessel’s name, call sign, type and position. Through AIS data transmitted to Navipac technology onboard C/S Cable One, maps of the cable trace and echolocation the route of the guilty ship in relation to the buried cables was identified.

Divers from JD-Contractor A/S then used underwater cameras and a ROV, to find the anchor trace, which was found to be approx. 1.5 m wide and 0.6 m deep.

By following the anchor trace, the fault in the cable was localised. Divers then mounted lifting straps and fitted taifun wire so both cable ends were ready for lifting. Due to the risk of water damage between joints 33 and 34, the whole length of cable approx 2.4 km between the two was retrieved. When the weather improved 2.5 km of new cable was severed, made water tight and layed.

After the cable was laid, M/S Marcos was used as a platform for splicing the cable ends supported by the tug T/B Naja.

Bad weather delayed the start of the repair, but the splicing of the cables was completed in only 3.5 days.