Wind turbine sizes are increasing at an unprecedented rate and for clear reason. The bigger the turbine, the more power it can generate and the fewer are needed per wind farm. Taller turbines require larger foundations to withstand heavier winds further out to sea, but as these foundations grow, they are becoming increasingly challenging to lift and transport. As an expert in handling heavy items safely and efficiently, Mammoet has been ahead of the curve in coming up with ways to make the movement of even XXL monopiles faster and more cost-effectively.
While it is theoretically possible to place monopiles into the sea using large crawler cranes, those required to meet the lifting capacity of the installation vessel would have been too big, requiring more space than was available at the port, and also reinforcement of the ground.
Mammoet engineered an upgraded terminal crane that can lift mega monopiles into the water for offshore feedering, and a specialist patented jacking-and-cradle system for their safe handling, using its SPMTs. Mammoet’s equipment transformed the port of Ronne in Denmark into a seamless assembly line where monopiles were efficiently offloaded, stored, capped and then lifted into the water and no civil work was needed to reinforce the quay. This value was demonstrated during the marshalling scope for Windanker GmbH’s 315 MW Windanker offshore wind farm, which was being fed by Van Oord in the German waters of the Baltic Sea.
Better support and less civil work
The transport and installation of the 21 monopile foundations were overseen by Van Oord with Mammoet supporting their onshore lifting and transport. The monopiles arrived at the port of Ronne from Spain, shipped in seven batches. The heaviest monopile weighed 2150 tons and measured approximately 87 metres in length.
Fitted with Mammoet’s XXL monopile transport system, 90 axle lines of SPMT lifted them off their grillages and cradled them securely as they were driven off the vessel. They were then taken to a temporary storage location and placed onto sand bunds, ready to be called off for capping to make them watertight.
The added stroke of the XXL monopile transport system allowed the monopiles to be lifted higher so that the indents of the storage bunds could be deeper, improving their support while using fewer materials. Next, at the capping location, a large LR1750 crawler crane installed plugs onto the top and bottom ends of each monopile.
Once both plugs were installed, the monopiles were driven to the quayside in front of the two MTC1600 cranes, which Mammoet developed specifically to lift XXL monopiles onto vessels and into waters. Once each monopile was safely in the sea, it was towed using tugs to Van Oord’s specialist heavy lift installation vessel, the Svanen, which was ready in the field to lift and install it into the seabed.
“We made a completely new crane design for this project, which is not typical but something we felt was necessary with the growth of monopile foundations,” explains Stefan de Vries, project manager at Mammoet. “Once everything was agreed, we needed to ensure the new MTC cranes would be ready. We collaborated with Van Oord to make sure they would suit their needs.
Initially, it was planned that the cranes would lift 2800 tonns, but we suggested their maximum capacity match that of the Svanen to ensure consistent limits across the project. So, we increased their combined lift capacity to 3200 tons”.
Foundations for success
With the ballast weight of the MTC crane positioned much further away from the pivot point of the boom in comparison to a large crawler crane, the load-bearing pressure was far less. This helped to spread the load over a greater distance, avoiding the need for specialist foundations or temporary civil work. Thanks to the efficiency of crane lifting compared to Ro-Ro operations, the Svanen could remain in the field and be constantly fed monopiles.
The result was that an otherwise challenging marshalling project was made simpler through a combination of knowledge, innovation and collaboration. With considerable experience of monopile handling, Mammoet guides its customers to the safest and schedule boosting methods to simplify complex marshalling projects. It is also constantly innovating to ensure its transport and lifting solutions can support not just the wind farms of today, but those of tomorrow.
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