Supporting Construction of Next-Gen Floating Offshore Wind Turbines

While windy locations naturally make ideal spots for offshore wind farms, they bring challenges when it comes to assembling wind turbines — particularly in ports.

Most wind turbines have fixed foundations and are assembled at sea using powerful installation vessels that are specially designed to withstand strong winds. Floating wind turbines can be installed in deeper waters and deliver much higher power yields.

However, the movement of their foundations means they must be assembled in the calmer waters of ports — their towers, nacelles and blades constructed on their buoyant bases before being floated out as complete units.

As years pass, the size of these turbines is steadily growing — which means that some of the world's largest cranes are now needed to assemble them at port.

The Eoliennes flottantes du Golfe du Lion (EFGL) wind farm is a joint venture between Ocean Winds and Banque des Territoires. With this project, floating wind technology will reach its third generation and so mature towards mass deployment.

Mammoet was approached by Euroports to support with the marshalling — and assembly — of the components that make up the three turbines at Port-la-Nouvelle, in France.

Its engineers managed the entire operation in often turbulent weather conditions. The project is in one of the windiest areas in France, where speeds can reach 22 miles per hour.

Foundations for Success

Mammoet was brought in at the planning stage of the project to advise on what crane would be best suited for the job and how to ensure a smooth transition from component delivery to construction. Its approach was to ensure that all the components for all three floating wind turbines were delivered to the port well in advance of assembly, to de-risk subsequent stages given the high probability of wind delays.

A large crawler crane, the CC8800-1, was chosen as the main crane for the heavy lifts. It was supported by two 220-ton mobile cranes for tailing operations.

"With jobs like this, you must use a powerful crane with a big outreach capacity, because the foundations are moored next to the quayside" said Yan Billard, managing director of Mammoet France."We used a CC8800, which has a 1,600 tonne (1763 ton) capacity, fitted with a boom booster to create a 144-meter (472 ft.) main boom. The booster is a special section that increases the capacity of the crane to enable higher lifting within a small radius".

So that the quay could take the full weight of the CC8800 during lifts, an area measuring 131 sq. ft. was created that could sustain a ground bearing pressure of 33 tons per sq. ft. The ground was reinforced with two layers of wooden mats, laid over gravel to ensure a flat foundation.

Twenty-four lines of Mammoet self-propelled modular transporters (SPMTs) were used to transport the components inside the port — driving them from the quayside to a laydown area, before returning them for assembly.

The first components were offloaded in summer 2024, with deliveries arriving from the Netherlands. The three floating foundations were fabricated in For-sur-Mer and took a day of towing to reach Port-la-Nouvelle.

Managing the Unmanageable

Once all the components were in their storage areas, and the floating foundations temporarily moored near the entrance of the port, the project moved to the assembly phase.

Mammoet's scope was to bring each component, in the right order, underneath the hook of the crawler using SPMTs. The CC8800 would then lift them into position so they could be bolted together.

The operation began with the three tower sections (the bottom, middle and then top), followed by the nacelle, and then finally the three blades. The heaviest item was the 419-ton nacelle.

Due to electrical components inside, the bottom tower sections were stored beside the CC8800 in a vertical position. The other two sections were tailed into an upright position using the mobile cranes and the crawler.

"The wind presented the biggest challenge when it came to the lifts," said Billard. "When it exceeded speeds of 10 meters per second (22 mph), lifting had to pause. It is a very windy area, and we were aware of this, but knew this was something we would have to manage effectively. Safety is always the top priority".

Once all the components were connected, the turbine was moved by tugs to a different section of the quay for final assembly work to take place before the final load-out.

Mammoet's considerable experience in planning and supporting successful offshore wind projects makes it a perfect partner for de-risking projects in challenging environments.

While the strong winds were unavoidable during the lifting stage, through planning minimized their impact on the delivery stage.

By ensuring all equipment and components were on site ahead of time, this ensured unnecessary downtime was avoided and all lifts could be performed safely.

For more information, visit mammoet.com.