Fugro has secured a contract from German transmission operator 50Hertz to investigate unexploded ordnance risks along the planned offshore cable corridors for the LanWin3 and LanWin6 grid connections in the North Sea.
The two high-voltage direct current links are each designed to transmit up to 2GW of offshore wind electricity, providing a combined planned connection capacity of 4GW. Fugro’s contract addresses seabed hazards ahead of cable installation; it is not an award to manufacture or lay the cables.
The initial survey programme is scheduled to begin in the second quarter of 2027. It will cover corridors 200 metres wide along the proposed routes, using two Geowing fixed magnetic gradiometer arrays fitted with ten magnetic sensors each.
Magnetic measurements will be processed to identify potential targets on or beneath the seabed. The resulting master target list will guide further investigation and decisions about whether any objects need to be moved, avoided or subjected to specialist clearance.
Inspection and identification activities are planned for 2028, with remotely operated underwater vehicles and additional detection systems examining selected targets. Fugro will also support the removal and disposal of confirmed unexploded ordnance, subject to the relevant procedures and regulatory requirements.
The number of potential hazards is not yet known. That uncertainty is precisely why the survey precedes the detailed clearance programme, and it would be inaccurate to report that unexploded devices have already been located on the routes.
Historic military activity has left potentially hazardous objects in parts of the North Sea. Some may lie on the seabed while others have become buried or obscured by sediment, making direct visual inspection insufficient as an initial survey method.
Magnetic gradiometry measures spatial differences in the magnetic field. Ferrous material can produce anomalies whose position and relative characteristics help survey teams identify areas requiring attention.
An anomaly does not establish that the source is an explosive device. Metallic debris, discarded equipment and other man-made objects can produce a detectable response, while burial depth, object size and composition influence what the equipment can identify.
The spacing and positioning of sensors affect survey coverage and the resolution of the resulting data. Using multiple sensors within a fixed array allows Fugro to gather measurements across a defined swathe as the system travels along the corridor.
These measurements must be corrected and interpreted before a target list can be assembled. Positioning accuracy also matters because underwater investigation equipment must be directed to the correct location when the second phase begins.
Remote inspection can provide visual and instrument readings that help specialists distinguish debris from potentially hazardous objects. Sediment conditions, visibility and object accessibility may constrain the inspection, making the choice of investigation method site-specific.
The final response to any confirmed ordnance will depend on its assessed condition and the applicable authorisations. Fugro has not disclosed a standard removal technique for the entire project or stated that all targets will require disposal.
Submarine cable construction can disturb the seabed during route preparation, trenching and burial. A hazard encountered during those operations could interrupt equipment movements and create risks to vessels, personnel or the surrounding environment.
Early investigation enables the project team to plan protective measures before committing cable installation equipment to a particular section. Route changes may also be considered where technically and legally appropriate, although altering an approved alignment can introduce separate design and permitting requirements.
LanWin3’s planned offshore connection runs from a wind farm area about 120km north-west of Helgoland to the German mainland near Büsum. The 50Hertz project description identifies an offshore cable route of approximately 200km and a further land connection of about 15km towards the Heide area.
The LanWin3 system is planned for 525kV direct-current operation and up to 2GW of capacity. Its offshore converter station will connect the generation infrastructure to a transmission system designed for delivering electricity over a substantial distance.
High-voltage direct current is used for long offshore connections partly because long alternating-current cables introduce capacitive effects that can influence the transmission system’s performance. Converter equipment is therefore an integral part of the electrical project rather than simply an accessory to the cable.
The cable corridor survey is separate from the engineering and manufacture of that converter equipment. It establishes information about seabed conditions and hazards that may affect the physical installation route.
According to 50Hertz, the expected completion date for LanWin3 is 31 December 2032. Fugro’s 2027 and 2028 survey activities precede that wider construction milestone, while LanWin6 has its own project programme.
Fugro has not disclosed the survey contract’s value or a confirmed number of ordnance targets. The next measurable outcome will be the magnetic survey dataset and resulting target inventory, followed by investigation and clearance decisions in 2028.
