• 51 foundations
  • 50 wind turbines
  • 186000 families supplied with green electricity

With the purchase of the Vole au vent, Jan De Nul confirmed its position in the offshore wind market. The vessel embarked on its first major mission under the umbrella of Jan De Nul in 2016: the installation of 50 offshore wind turbine foundations with accompanying wind turbines, and the installation of the offshore substation foundation. The design, construction and assembly were part of Jan De Nul’s contract: a comprehensive project with major challenges.

"The first major project of our new vessel."

“We landed the project at the end of 2015 and started right away because there was little time. We were responsible for most of the subcontractors within the project. From the very start of the project, we consulted closely with them and followed up their progress”, says project manager Koen Marchand.

The job of the Vole au vent was two-fold: the installation of the foundations and of the wind turbines. The steel foundations consist of two parts: a monopile (MP), which is piled into the seabed, and a transition piece (TP) on top of the monopile that makes the connection with the turbine. In all, there were 51 foundations: 50 for the wind turbines and one as the base platform for a transformer station. Our client was Nobelwind, a project company of Parkwind, an affiliate of Colruyt, the main shareholder and developer. The wind turbines have been installed on a sandbank, the Bligh Bank, and are part of the Belwind wind farm.

“We sent our own people to the steel construction companies to keep an eye on progress and inspect the execution and the quality”, says Koen. At the same time, Jan De Nul’s project team worked out the installation methods and the equipment of the Vole au vent and bought all the necessary equipment for the installation of the wind farm. During the entire campaign, the port of Ostend served as operating base and marshalling port. 

From vessel to solid platform

The Vole au vent is a jack-up offshore installation vessel that can transform into a stable platform at sea. “We lower the four legs, allowing the vessel to lift itself out of the water, a process also known as jacking”, says Technical Superintendent Kris Van Limbergen. The place where the vessel is jacked is always determined in advance because the sea bed must be strong enough. “For each project, we completely renovate the vessel. Each time, we start from an empty deck and install all the equipment and all parts. For Nobelwind, we were able to take four complete foundations on board for each trip, i.e. four monopiles and four transition piece.”

The installation works started in May 2016. The monopiles are up to 80 metres long and have a five-metre diameter. They are firmly piled into the seabed and come out a few metres above sea level. On the seabed, each monopile is surrounded by rocks that were placed there earlier by the fall pipe vessel Simon Stevin to counter erosion from the sea bottom caused by sea currents. Koen Marchand: “We used the large crane of the Vole au vent to lift each monopile and place it vertically on the seabed. Then we piled the monopile through the sea bed with a large hydraulic hammer. It is of course crucial that the pile stands perfectly vertical, otherwise the wind turbine wouldn’t be vertical, its efficiency would decrease, and the structure would have to bear a higher load than allowed. We passed this challenge with flying colours, achieving a vertical accuracy of 0.1 degree!” The transition piece was then attached on top of the monopile using 84 bolts of 25 kilos each.   

Installation

October 2016 was the start of Jan De Nul’s second campaign: the installation of the wind turbines themselves. First, the deck of the Vole au vent underwent a complete transformation at the shipyard in Vlissingen. “We first removed 450 tonnes of steel sea fastenings and structures and built a new 350-tonne structure to accommodate the wind turbines on board”, says Koen.

Challenge

With all wind turbines installed by early April 2017, a final coating campaign followed during which any damaged paintwork was touched up. The project was fully completed and commissioned in October 2017. “I am very proud of this project”, says Koen Marchand. “This was the first major project for our new vessel. Thanks to good preparation, our confidence and experience to manage big projects and also thanks to the excellent cooperation with our client and subcontractors, the project was completed within time, in full compliance with the contractual requirements. It was quite a challenge but we succeeded in bringing it to a perfect end.   This project summarises exactly what we stand for: we approach the works thoroughly and however new the challenge might be for us, we manage successful completion.”

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