Mammoet has completed the transport and weighing of three major offshore substations for the Dogger Bank Wind Farm, which will be the world’s largest offshore wind project once finished.
Dogger Bank is being built in three stages — Dogger Bank A, B and C — by SSE, Equinor and Vårgrønn. When complete, it will have a capacity of 3.6GW and generate enough energy to power about six million homes each year.
The three substations were fabricated by Aibel, with steel construction starting at the company’s yard in Thailand before being shipped to its Haugesund yard in Norway for installation of transformers and other complex components. The substations will collect and convert electricity from the wind farm before it is sent to shore.
With fabrication split between two countries and a specialist vessel required to move the structures, the project called for careful coordination of equipment and personnel.
Hundreds of axle lines across two countries
Mammoet supported Aibel across all three phases of each substation move: load-out in Laem Chabang, Thailand; load-in at Haugesund, Norway; and final weighing and load-out for transport to the North Sea.
One of the biggest challenges was sourcing the large number of Self-Propelled Modular Transporters (SPMTs) required at both locations. In Thailand, Mammoet used 338 axle lines to move the 7,500-tonne substations. In Norway, 264 axle lines were used for the load-in, with another 80 required for weighing and final load-out once the structures reached 9,350 tonnes.
In total, 682 axle lines were sourced from Mammoet’s global fleet of more than 5,000 and shipped to both countries by sea and by road.
Each transport phase faced its own engineering and logistical challenges, including tidal conditions and precise SPMT configurations. The SPMTs lifted the substations using their onboard stroke before transferring them to or from oceangoing vessels.
Close cooperation between Aibel and Mammoet engineers led to the design of special grillage beams that allowed loads to be transferred safely to the strongest points of each topside. Aibel also fabricated two custom load-out frames to keep the substations secure during transport.
In Thailand, the team had to drive the substations 1km over public roads to reach the port. Fences were removed and a temporary gravel slope was built so SPMTs could avoid the main entrance. The substations were then moved onto a heavy-load carrier via RoRo ramps, with SPMTs lowering them onto vessel grillages before disembarking.
Each substation took 45 to 50 days to reach Norway, where higher ground-bearing pressure requirements meant fewer axle lines were needed for load-in. The structures were then moved to Aibel’s yard for final fabrication and placed on temporary supports.
Before the final load-out, 36 weighing jacks and load cells were used to determine the weight and centre of gravity, with the process repeated three times for accuracy. For the final transport, 344 axle lines were required.
Mammoet also supported the barge ballasting, using 16 submersible pumps — each capable of moving 1,000 cubic metres of water per hour — to keep the vessel level during load transfer.
Learnings across three years
The repeated operations across three years allowed the team to refine processes and improve efficiency. As a result, the load-out of the Dogger Bank C substation in Thailand was completed a full day faster than earlier phases.
“One of the things Mammoet does so well is to be flexible,” said Dorien Frequin, Branch Manager Norway at Mammoet. “We help our clients whenever there are small changes to their plans, and our teams work together to adapt to these changes.
“Our engineering department works closely with our project managers, who work closely with our planning team to source the equipment needed, and that can all happen in a very short timeframe”.
The Dogger Bank substation transports highlight the scale of the global effort behind the project, with meticulous planning, technical collaboration and extensive equipment mobilisation central to its success.