A new method for handling large offshore wind turbine foundations has made the work of moving and installing them faster and more cost effective at the port of Rønne.
The technology was used for the Windanker offshore wind farm in the German Baltic Sea, which is being built by Van Oord.
The large steel foundations, known as XXL monopiles, are used to support taller wind turbines that generate more power. These monopiles are extremely heavy and difficult to handle. The largest units in the project weighed about 2,150 tonnes and measured around 87 metres in length.
Mammoet, a specialist in heavy lifting and transport, developed a new terminal crane along with a dedicated handling system using Self-Propelled Modular Transporters. The system allowed the monopiles to be lifted from vessels, stored at the terminal, sealed to make them watertight and then moved into the water without the need for additional quay reinforcement.
Once afloat, the monopiles were towed by tugboats to Van Oord’s heavy lift vessel, the Svanen. From there, the vessel transported them to the offshore wind farm site, where they were installed on the seabed.
Mammoet project manager Stefan de Vries said the scale of the monopiles required a different approach. “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,” he said.
Stefan said Mammoet worked closely with Van Oord during the planning phase to ensure the equipment matched the installation vessel’s requirements. “Initially, it was planned that the cranes would lift 2,800 tonnes, 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 3,200 tonnes,” he said.
Mammoet said the new setup spread loads more evenly and removed the need for extensive civil works at the port. The company said the approach simplified a complex operation and reduced time and cost.
The solution is expected to support future offshore wind projects as turbine sizes and foundation weights continue to increase.