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A Global Balancing Act for the World’s Largest Offshore Wind Farm
Moving a single offshore substation is complex. Moving three of them—each weighing up to 9,350t—across two continents while keeping fabrication on schedule demands a level of coordination few projects ever see. That was the reality behind the handling of the Dogger Bank A, B, and C topsides, where Mammoet supported Aibel’s multi-yard construction program for what will become the world’s largest offshore wind farm.
Split between fabrication yards in Thailand and Norway, the project required hundreds of SPMTs, bespoke steelwork, and vessel transfers that had to land on the minute. Dogger Bank’s scale alone would turn heads: 3.6GW of capacity and enough power to supply six million homes. But it was the logistical choreography behind the substations that delivered the real story.
The Challenge: Hundreds of Axle Lines in Two Locations
At first glance, the numbers almost feel abstract. In Thailand, Mammoet deployed 338 SPMT axle lines to move the 7,500t structures from fabrication halls to the port at Laem Chabang. In Norway, another 344 axle lines were needed for the load-in, weighing, and final load-out. All told, the project consumed 682 axle lines—sourced from a global fleet, shipped on container vessels, and delivered just in time.
The sheer movement of equipment became a project of its own. Roads needed removal of fences and construction of temporary gravel slopes to allow the convoys to reach the port. In Norway, higher ground-bearing capacity meant fewer SPMTs were needed, but the complexity didn’t disappear—it simply shifted.
Engineering for the Strongest Points
Aibel and Mammoet’s engineers worked side by side to create special grillage beams, ensuring that loads were transferred precisely to the topsides’ strongest structural points. Two custom load-out frames were built, one of which made the full journey from Thailand to Norway and remained in service for all three substations.
When the modules rolled onto the heavy-lift vessel via RoRo ramps in Thailand, SPMTs lowered them onto the ship’s grillages before being disconnected and driven off. Each transit to Europe lasted 45–50 days—a reminder of the long tail of offshore logistics, where months of travel separate fabrication and installation.
Three Weighings, One Final Measurement
Once in Haugesund, each substation underwent final assembly before being weighed using 36 jacking points and loadcells. Engineers repeated the weighing three times for accuracy, calculating both final weight and center of gravity—critical data for offshore installation.
For the last phase, the substations—now heavier with transformers and electrical equipment—required 344 axle lines for the final load-out. Mammoet’s ballast team ran 16 submersible pumps, each capable of moving 1,000 m³/hr, to keep the barge level during transfer.
Lessons Learned—and Saved Days
Over three years, experience accumulated. By Dogger Bank C, the team eliminated a full day from the Thailand load-out schedule. As Dorien Frequin, Branch Manager Norway at Mammoet, put it, flexibility was the secret weapon: “We help our clients whenever there are small changes to their plans and our teams work together to adapt to these changes.”
