Inch Cape Completes 18-Month Campaign to Relocate More Than 26,000 Seabed Boulders Ahead of Offshore Wind Construction. The Inch Cape Offshore wind project has concluded a major pre-construction operation, with a total of 26,402 boulders relocated across the project's offshore footprint in the Firth of Forth after an 18-month program of survey and clearance work.

Scale of the Operation

The boulder relocation program covered an extensive area of the North Sea seabed, stretching along an 85-kilometer export cable corridor and across 150 kilometers of array cable positions, as well as around each individual foundation location and at the offshore substation platform site. Every boulder was moved within Inch Cape's consented boundaries, relocated between three and 150 meters from its original position.

The cleared path is now intended to enable the core phases of offshore construction, including cable installation and burial, foundation installation, and wind turbine construction, the latter to be carried out by the jack-up vessel Wind Mover.

Ancient Origins of the Boulders

The boulders were deposited on the seabed during the last glacial period, left behind by retreating glaciers in the Firth of Forth region as the ice sheets withdrew approximately 11,500 years ago. Their sizes varied considerably, ranging from 30 centimeters to 2.5 meters in diameter, presenting a wide range of logistical challenges for the teams tasked with clearing them.

Equipment and Contractors

The boulder relocation campaigns were carried out as part of the engineering, procurement, construction, and installation array cable contract that Inch Cape awarded to TKF.

The physical clearance work was performed by marine contractor N-Sea, whose crews operated around the clock, working 24 hours a day, seven days a week, aboard three multi-purpose vessels: FS Aries, 4-Winds, and Pathfinder. Initial geophysical surveys to map and identify seafloor anomalies were conducted using the modern hybrid survey and support vessel Geo Ranger.

The boulders were moved using remotely operated vehicles and auxiliary remotely operated vehicles fitted with a boulder grab attachment, which picks up individual boulders and transfers them to positions outside the construction areas.

N-Sea's multi-purpose AUXROV system is designed for heavy-duty subsea tasks and can be configured with various tools, including boulder grabs, excavators, and cutting tools. Operators monitored and controlled the ROVs and AUXROVs from dedicated control rooms, known as ROV containers, located onboard each vessel.

Regulatory Oversight and Fishing Industry Coordination

The relocation work was authorized under marine licenses granted by the Marine Directorate. Following completion of the campaigns, the coordinates of all boulder locations were provided to the Scottish Fishermen's Federation for distribution to the local fishing industry, allowing fishermen to account for the repositioned seabed material in their operations.

Status and Next Steps

Inch Cape confirmed that while some additional individual boulders may still need to be relocated in response to specific engineering requirements that arise during the installation phase, the planned boulder relocation campaigns are now formally complete. The clearance of the seabed marks a significant milestone in enabling the construction phase of the offshore wind project to proceed across its full footprint.

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