Fugro wins LanWin3 and LanWin6 seabed surveys

Fugro has secured a contract from German transmission system operator 50Hertz to survey and investigate unexploded ordnance along the planned LanWin3 and LanWin6 offshore electricity cable routes in the North Sea.

The two high-voltage direct current (HVDC) connections are designed to transfer up to 2GW of offshore wind generation each, providing a combined planned transmission capacity of 4GW. Fugro’s assignment covers seabed investigations, identification of potentially hazardous objects and support for clearance operations before cable installation.

Initial survey work is scheduled to begin in the second quarter of 2027, covering corridors approximately 200 metres wide along both proposed routes. Fugro will deploy two Geowing fixed magnetic gradiometer systems, each fitted with ten magnetic sensors, to detect anomalies associated with objects located on or beneath the seabed.

The measurements will be used to identify potential targets and create a master target list for further investigation. Follow-up inspection and identification activities are planned for 2028, using remotely operated vehicles and specialist detection equipment to examine selected objects and remove debris where necessary.

Confirmed unexploded ordnance will require a different response from ordinary metallic debris. Fugro’s scope includes supporting its safe removal and disposal in accordance with the applicable regulatory requirements, allowing the cable routes to be prepared for subsequent installation operations.

Unexploded ordnance remains a hazard in parts of the North Sea because of historic military activity, including the disposal and loss of munitions. Objects may be exposed on the seabed or buried beneath layers of sediment, making their presence difficult to establish through visual inspection alone.

Magnetic gradiometry provides a means of identifying potential hazards before intrusive investigation begins. Ferromagnetic objects affect the surrounding magnetic field, producing measurable anomalies as a sensor system passes over them. An array of sensors allows measurements to be collected across a survey swathe, helping investigators locate and assess targets along a proposed cable corridor.

The resulting measurements do not identify an explosive device with certainty. Scrap metal, discarded equipment and other ferrous material can produce magnetic anomalies, while the strength and form of a response depend on the object’s characteristics, orientation, burial depth and distance from the sensors.

Interpretation therefore requires the survey data to be assessed alongside seabed conditions and the proposed installation route. An anomaly may indicate an object requiring further examination without establishing its precise identity. The 2028 investigation programme will address that uncertainty through closer inspection and additional measurements at selected locations.

Remotely operated vehicles provide access to the seabed without requiring divers to undertake every inspection. Depending on the equipment deployed, they can collect visual information, position additional sensors and support controlled intervention activities. Their use must still account for water conditions, visibility, seabed disturbance and the risks associated with potentially explosive material.

When an object is identified as unexploded ordnance, the appropriate treatment depends on its type, condition and position relative to the planned infrastructure. Moving or disposing of munitions involves separate safety and environmental considerations, and specialist procedures are needed to determine how any confirmed hazard should be managed.

The survey programme precedes the installation of submarine electricity cables because seabed obstructions can affect both construction safety and the long-term condition of the infrastructure. Cable installation equipment must operate along a route with sufficiently understood ground conditions, while burial tools and protection systems must avoid hazards that could damage equipment or interrupt installation.

Submarine cables are vulnerable to external mechanical forces during installation and operation. Burial can reduce exposure to anchors, fishing equipment and certain seabed activities, but its feasibility depends on sediment characteristics, obstructions and the depth that installation equipment can achieve.

Route investigation therefore contributes to decisions about cable positioning, burial methods and any locations requiring additional protection. Where a hazard cannot be removed or the seabed is unsuitable, engineers may need to consider alternative installation arrangements within the limits of the approved route and its environmental permissions.

The electrical role of LanWin3 and LanWin6 is separate from this marine investigation work. Both projects form part of Germany’s programme to connect additional offshore wind generation to the national transmission system. They are designed around large HVDC transfer capacities, requiring offshore and onshore electrical infrastructure in addition to the submarine cable routes.

In an offshore HVDC connection, electrical equipment converts alternating current from the wind generation network into direct current for transmission. At the receiving end, converter equipment provides the necessary interface with the alternating current electricity system. Transformers, switchgear, control systems and protection equipment are required to manage the connection and maintain operation within its technical limits.

The capacity of the electrical link does not determine its annual energy transfer independently of the connected generation. Actual deliveries will depend on the wind farms’ output, equipment availability and any constraints affecting the wider electricity network. The planned 4GW combined rating describes transmission capability rather than a continuous generating output.

The individual engineering packages must be coordinated across multiple delivery stages. Offshore converter structures, cable manufacturing, marine surveys, route preparation, installation and electrical commissioning can proceed under separate contracts, but their interfaces influence the overall programme.

50Hertz has already awarded other work associated with LanWin3, including the offshore converter platform package. Fugro’s contract addresses a different requirement within the same wider grid development: establishing the condition of the proposed seabed corridors and identifying hazards that must be resolved before cable-laying operations.

Survey findings may affect the amount of clearance work required and the time available for subsequent cable installation. The number, location and condition of suspected explosive objects cannot be established in advance of the investigation, so the survey results will help determine the scope of the next phase.

The programme also requires coordination between marine investigation teams, engineering contractors and the organisations responsible for permissions and environmental compliance. Locations selected for intrusive examination or clearance may require specific operating controls, particularly where potential hazards overlap with protected or sensitive marine areas.

Fugro’s initial magnetic survey campaign is expected to begin in the second quarter of 2027. The resulting target register will form the basis of the detailed inspection and identification activities planned for 2028, before the relevant cable corridors can be prepared for installation.