MacArtney Provides Subsea Infrastructure Solution at Fehmarnbelt Fixed Link

MacArtney Provides Subsea Infrastructure Solution at Fehmarnbelt Fixed Link

MacArtney's subsea infrastructure supports the immersion, connection and recovery activities required to place tunnel elements on the seabed. Illustration: Copyright Femern A/S

At the Fehmarnbelt Fixed Link between Denmark and Germany, MacArtney worked closely with Femern Link Contractors (FLC) to deliver an integrated subsea infrastructure solution supporting the controlled positioning of tunnel elements on the seabed.

The tunnel spans approximately 18 kilometers and is laid at depths of up to 40 meters below the sea surface. Three of the 89 tunnel elements have now been successfully immersed and connected as construction of the Fehmarnbelt Fixed Link continues.

Standard elements measure 217 meters in length and 42 meters in width, and each immersion involves floating a 73,500-ton tunnel element out of the work harbor, towing it offshore, lowering it into the shallow seabed trench, and guiding it into final position.

Based on an initial concept developed by FLC, MacArtney helped refine the system design through iterative engineering as installation methods and operational requirements evolved throughout the project. With design, testing, project management and on-site support based in Denmark, frequent interaction, prototype validation and ongoing optimization shaped the configuration ultimately used in the field.

The resulting power and connectivity infrastructure spans tunnel elements and the modular Immersion Pontoons IVY 1 & IVY 2, supporting positioning, monitoring and control during immersion.

Prior to immersion, Retrieval Frames are connected above water to pre-installed Bulkhead Connector Plates. Equipped with cameras, lighting and actuators, they enable monitoring and controlled operation during the connection and release sequence. This configuration supplies power and data to pumps and sensors within the tunnel element. Once positioning is complete, the Retrieval Frames are disconnected and recovered by a remotely operated vehicle (ROV).

Supporting this is a broader infrastructure comprising umbilicals containing power, Ethernet, and coax cables, including integrated SubConn connectivity that enables power and data transmission between topside systems and tunnel elements.

The system also incorporates control units for power distribution and data handling, MacArtney stress terminations, armadillos, mounting frames, NEXUS multiplexers and junction boxes installed on tunnel elements and aboard the Immersion Pontoons.