In May 2012, the joint venture DONG Energy / ScottishPower Renewables contracted Offshore WindForce to install the foundations for 108 3.6 Mw wind turbines in the Irish Sea west of Barrow in Furness. The wind farm is situated next to the already operational windfarms, Walney 1 and 2.
Offshore WindForce (OWF) is a joint venture between Volker Stevin Offshore and Boskalis Offshore. VSF contributed fully in the tendering phase and was a shareholder of VSO when the work was contracted. In the meantime, VSO has become an independent entity in the VolkerWessels Group, but VSF's contribution to the project remained unchanged in the form of organising the hydraulic hammers (IHC Hydrohammer types S2000 and S1400), grouting plant and the manpower for the manufacture and execution. Globally, the work for OWF comprised transporting the foundations from Aalborg in Denmark to Belfast in Northern Ireland and installing those foundations in the Irish Sea with two crane ships provided by the client. The engineering, manufacture and installation of the necessary hoisting equipment, temporary constructions and see fastenings for use on the ships was also part of the assignment. Prior to the installation work by OWF, a rubble layer was deposited at the site of each foundation to prevent erosion of the seabed round the monopiles and, once the cables have been fitted between the wind turbines, a further layer will be laid to protect them. A new quay wall has been constructed in Belfast for this project, amongst others. Organising the port site for the storage and transshipment of the construction elements was also part of the assignment.
The foundations consisted of two parts: the monopile and the transition piece. The monopole was a tubular pile with a diameter of 6 or 5.6 metres with a conical top piece with a diameter of 4.75 m. The piles varied in length between 44 and 59 metres and in weight between 335 and 516 tonnes. The transition pieces were approximately 25 metres long and weighed 340 tonnes. The water depth at the site of the foundations was between 18 and 24 metres with a tidal range of a maximum of 8 metres. In April 2013 two ships, A2Sea's Sea Installer and Swire Blue Ocean's Pacific Orca, were mobilised at Keppel Verolme in Rotterdam. Temporary constructions were manufactured at various locations in the Netherlands beforehand. VSF also contributed here by making two upending buckets, which were used on board the ships for upending monopiles.
Starting in May 2013, the two ships installed a total of 108 foundations. The Sea Installer was able to carry three foundations at a time and the Pacific Orca 5. After 30 foundations, in accordance with the agreement, the Sea Installer was returned to the client for installing the towers, rotors and blades. In between May and the end of October 2013, the Pacific Orca installed the remaining 78 foundations. The installation of the foundations proceeded extremely smoothly. The Pacific Orca succeeded in executing a complete cycle (loading, sailing to the location, installing five foundations and sailing back to Belfast) in five days. One time, the installation of a foundation took as little as eight hours. Extensive preparation and the availability of the right, reliable equipment were essential for this success. In addition to a smooth execution, the work also proceeded highly successfully in terms of safety, without a single LTI (lost time injury). In addition to the work for OWF, VSF was involved in the installation of the wind farm's transformer station. In this substation, all the cables from the wind turbines come together, after which the electricity is transported via two export cables to Heysham and connected to the British electricity grid. The substation consisted of a jacket and topside and was placed by the firm of Scaldis' floating crane, Rambiz. VSF performed the piledriving and connected the piles to the jacket with grout. The turbines will be installed up until mid-2014, after which it should be possible to supply the first electricity to the British electricity grid from October 2014 onwards. Ultimately, the West of Duddon Sands Windfarm will be able to provide 300,000 households with electricity annually.