James Fisher Subsea has identified 37 positive unexploded ordnance (UXO) targets at the site of the proposed 111MW Nordergründe wind farm in the German part of the North Sea.
The contract, with German wind farm developer, wpd, required the JF Subsea team to locate, excavate, and identify targets so any unexploded devices could be safely detonated by German authorities.
According to the company, the job posed technical complications because the shallow water around the Nordergründe site is tidal and can be rough meaning the teams had to work in zero visibility.
Two vessels were deployed, both with ROV teams onboard. Specialist divers were used by day and ROVs worked at night to speed the clearance process.
Bob Macmillan, technical diving director at JF Subsea said: ”Although much of the ordnance we retrieved turned out to be normal debris (such as anchors, chains and wires), the area is littered with UXOs (shells and grenades from both world wars) and our search identified 37 positive targets – some with multiple devices.”
UXOs deemed safe to move were cleaned and identified then returned to the seabed for ‘wet storage’. They could then be picked up later and transported to a designated sandbank which dries out at low water so they could be disposed of by officials. Provision for any deemed unsafe was to attach them to a large airbag and to tow them to a safe spot for controlled detonation.
”Many wind farms in this area face these UXO problems, and the additional experience we are getting with this contract puts us in a great position to tender for more contracts of a similar nature in the future,” Macmillan said.
Nordergründe is being constructed at a water depth of 10m, approximately 15km north-east of the island of Wangerooge. The wind farm will feature 18 Senvion Type 6.2M126 turbines scheduled for commissioning by the end of 2016.