SylWin Alpha Jacket and Platform Installed

Dutch offshore companies realised a unique operation in the North Sea. Under the direction of Seaway Heavy Lifting, one of the world’s largest convertor platforms – a ‘power socket at sea’ – is installed to the west of Sylt, the East Frisian Island.

Siemens built the SylWin alpha platform. It is so large and heavy that the ingenious ‘float-over method’ has been used to lift it from a pontoon onto the already installed ‘jacket’ (the base of the platform). This approach has been used successfully in the Gulf of Mexico and in the Far East, but is the first time that a platform as large as SylWin alpha was installed using the method in the North Sea.

Siemens commissioned Seaway Heavy Lifting (based in Zoetermeer, the Netherlands) to perform the unusual operation that in turn called in the assistance of maritime service providers Dockwise and Mammoet. The 14,000Mt SylWin alpha platform was transported on a pontoon that has been positioned in between the jacket legs. The platform was installed onto the legs of the jacket by ballasting the pontoon. Dockwise was responsible for this phase. Mammoet has then used jacks to lift the platform into its final position on the jacket. Final position of the platform was reached on Friday 18th July.

The 83-metre long, 56-metre wide and 26-metre high SylWin alpha platform is the largest of its type. Earlier this year, Seaway Heavy Lifting used its crane vessel Oleg Strashnov to install the 5,800Mt jacket. The Oleg Strashnov is one of the world’s ‘strongest’ crane vessels but it is not strong enough to lift the SylWin alpha jacket. Therefore, the decision was taken to add additional buoyancy in the form of buoyancy tanks and to ballast the pontoon on site. This complicated operation has been preceded by more than a year of preparatory work.

The SylWin alpha converter platform will serve as a ‘power socket’ for the DanTysk, Sandbank and Butendiek wind farms, which together comprise 240 wind turbines and represent a generating capacity of 864 megawatt. Grid manager TenneT, Siemens’ customer, is responsible for the connection of the wind farms to, in this case, the German high voltage grid. The SylWin alpha platform transforms the alternating current generated by the wind turbines into direct current that is transported via a 160-km long seabed cable and a 45-km long underground cable to the onshore Büttel high-voltage station.

As a contribution to sustainable energy provision, Northern Europe already has 40 offshore wind farms in operation, another 40 will be installed in the coming 10 years. TenneT, the grid manager, is installing the offshore electricity grid in the German and Dutch sectors of the North Sea to which the wind farms will be connected. Dutch offshore companies are playing an important role in installing the wind farms and the electricity grid.

Jan Willem van der Graaf, CEO Seaway Heavy Lifting: “With the installation of the 20,000 Mt (including its jacket) Sylwin alpha platform, Seaway Heavy Lifting and its partners have completed a challenging offshore operation. Our vessel, Oleg Strashnov, and crew did very well on the complicated jacket installation. In addition, a float-over this size is a first in the North Sea. Together this made for a signature offshore installation project. We see this as an excellent example of what Seaway Heavy Lifting has to offer the developing offshore wind sector in Northern Europe.”

Press Release, July 23, 2014; Image: Seaway Heavy Lifting