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The N05-A platform, the first wind-powered offshore gas platform in the Dutch North Sea, has been successfully loaded out, marking a significant step towards sustainable offshore energy. The platform, part of the GEMS (‘Gateway to the Ems’) project, sources electricity from the 113.4 MW Riffgat offshore wind farm and is expected to cut carbon emissions by over 85% during its operational lifespan.
HSM Offshore contracted Mammoet to handle the load-out of the 3,050-ton topside and 3,150-ton jacket at its fabrication facility in Schiedam, Rotterdam. The task involved complex engineering and heavy lifting expertise to transport both structures onto a barge for their journey offshore. The installation and offshore sailing phases were managed by ONE-Dyas, the platform’s owner.
Mammoet’s approach allowed the jacket to be assembled closer to its final installation site, reducing construction lead time. The jacket was fabricated in two sections, requiring heavy transport and upending operations using four mobile cranes—two LTM 1650 (650t) and two LTM 1450 (450t). A 750t mobile crane was used to install the pile sleeves. Once positioned, the upper section was transferred to the quayside, where two sheerlegs lifted it to allow the lower section to be maneuvered underneath for final assembly.
For the topside, Self-Propelled Modular Transporters (SPMTs) moved the structure from the fabrication facility to the quay. Mammoet also supported the installation of a pedestal crane onto the topside using conventional trailers and mobile cranes. Load cells were used to determine the final weights of both structures before the load-out operation commenced.
One of the major challenges was loading both the topside and jacket onto a single barge—an uncommon approach designed to optimize the schedule. This required careful planning to ensure enough space remained for installing pumps and winches on the transport vessel. Traditional mooring methods were not viable due to the combined weight of the structures.
“The mooring was quite critical, and we had to do a lot of engineering,” said Sven Segeren, Project Manager at Mammoet. “Normally, we would use a configuration of winches to moor and stabilize the vessel, but that wasn’t possible because of the force of the considerable loads. The loads on the winches were too high, and the bollards weren’t strong enough, so a small spud leg barge was used to keep the vessel stable before, during, and after load-out.”
The main barge underwent five days of preparation, including ballast equipment installation and pre-ballasting, before the final journey. The load-out of the jacket foundation and topside was executed in just two days, utilizing four trains of 32-axle-line SPMTs for precise movement.
Due to external factors, the exact load-out date remained uncertain for some time. To prevent disruptions to other projects at the HSM Offshore yard, Mammoet prepared a temporary load-in area at its own facility in Schiedam. Although this backup site was ultimately not required, it showcased Mammoet’s ability to adapt to changing project demands.
“We work a lot with HSM Offshore. They always involve us at the beginning of projects so we can help them with smart solutions for assembly,” added Segeren. “Through strong cooperation and early involvement, we were able to develop an efficient approach for assembling the jacket and reducing construction lead time.”
