Mammoet optimised two major decommissioning projects by integrating the load-in operations of the Heather Alpha and Eider Alpha topsides, reducing time and improving efficiency.
Working alongside Allseas, Mammoet managed the skidding of the 15,300-tonne Heather Alpha and 11,640-tonne Eider Alpha topsides after their removal from the UK North Sea. Both structures were lifted in single operations by the heavy lift vessel Pioneering Spirit and transferred to the cargo barge Iron Lady for transport to disposal yards.
A key advantage came during the planning phase, where Mammoet prepared the barge deck to accommodate both topsides, enabling a more efficient execution across a single campaign. The structures were later shipped to Frederikshavn, Denmark, and Vats, Norway, respectively.
The floating load-in operations required precise coordination, particularly during ballasting as the topsides moved between quay and barge. Mammoet engineered and installed skid tracks, beams and support systems to ensure smooth transfer.
“The clients wanted us to achieve the load-ins in 24 hours, but we managed it in half of that,” said Leo de Vette, Project Manager at Mammoet. “This required detailed planning and close collaboration with Allseas.”
Using up to 40 push-pull units, the topsides were skidded at controlled speeds over distances of 180 metres. Additional stabilisation systems ensured the barge remained secure throughout the operation.
