To whom it may concerns,
OVERDICK is proud to announce the successful installation of the SylWin alpha HVDC platform in the German Bight of the North Sea.
After the successful float-over of the topsides onto the jacket, the final phase of the installation was started with the jacking up of the 15000 tonnes topsides which was lifted to its design elevation 23 metres above sea levels by hydraulic strand jacks.
The platform stands 40 nautical miles WNW of the island of Sylt. Here, the platform will serve as the hub to connect the offshore wind parks Dantysk, Sandbank and Butendiek with the onshore substation at Buettel. The Siemens electrical plant fitted inside the platform is capable to transmitting 864 MW into the onshore power grid making it the most powerful converter substation installed in German waters to date.
OVERDICK on behalf of Siemens, the general contractor for the project, conducted the concept design and the structural detail engineering, as well as the transport and installation engineering.
The topsides’ record setting weight is beyond the lifting capacity of any offshore crane available. Therefore the design decision was made to conceive the platform as a float-over installation combined with self-elevating capability. The installation was conducted in three phases: following the initial installation of the jacket, the topsides was towed to the site and set down on the jacket by float-over. Finally a temporary hydraulic jacking system was used to elevate the topsides to the required height. In this way a conventional float-over, typically used in more benign waters of i.e. SE Asia, has been demonstrated feasible also in the North-Sea where this concept has never been followed up to now.
The installation of the 5600 tonne jacket was performed in April this year by means of heavy lift from a submersible barge. Due to the large lifting weight, the jacket was partially submerged to activate sufficient buoyancy to reduce the lifting load for the crane. Two temporary buoyancy tanks were fitted on the jacket to further increase buoyancy. After set down of the jacket on the sea bed, the tanks were recovered to the surface.
While the jacket’s 9 piles were being installed offshore, the preparations of the topsides were finalised at Nordic Yards in Warnemuende. The topsides, which had been assembled on its transport barge was floated out of the dry dock and towed from the Baltic Sea to the installation site in the North Sea. The barge was positioned over the jacket prior to initiating contact between the topsides’ legs and leg mating units by means of ballasting and hydraulic jacks.
Following the installations of the HelWin alpha and BorWin beta platforms, SylWin alpha is the third HVDC platform designed by OVERDICK installed in the North Sea. Together with the design of the Global Tech I and Borkum West II transformer platforms this success strengthens OVERDICK’s position as the leading engineering contributor to Germany’s offshore wind substation development.
With the design of the DolWin gamma platform already under way at OVERDICK, we look forward to further adding to this track record.
Andreas Rosponi, Reiner Klatte, Klaas Oltmann and Team