The 35 km² Westermost Rough offshore wind farm is located at about eight km off the east coast of England, next to the city of Hull. It was commissioned in the first half of 2015 and was constructed by a subsidiary of the Danish company DONG Energy, the largest operator of offshore wind farms.
Some 35 wind turbine generators (WTG) and one substation are installed at Westermost Rough, providing a total capacity of 210 MW. It is the first full scale commercial application of the Siemens 6 MW turbine. The WTG’s are installed on top of monopiles with a diameter of 6,5 m and weighing between 500 tonnes and 810 tonnes each. Transition pieces weigh around 367 tonnes each.
Manipulating such volumes and weights in offshore conditions is quite challenging. In addition, the 500 miles distance between the fabrication yard and the offshore installation site required thoroughful planning with regard to limiting off-time, decreasing operations cycle time, and economic execution of the project.
As the main contractor for the foundations, DEME-company GeoSea was responsible for load-out of foundations in Denmark, transportation to the UK, installation and grouting of the monopiles and transition pieces, and secondary works. Extensive preparation and engineering included the design and fabrication of a state-of-the-art gripper and lifting tools were necessary to achieve successful operations.
At Westermost Rough GeoSea set a new reference in that no onshore storage or marshalling was needed, and the foundations were immediately installed after transport from Aalborg, Denmark. The company assigned its heavy lift jack-up vessel ‘Innovation’, equiped with on on-boad 1.500 tonnes crane. By combining transport and installation in one operation, GeoSea was able to decrease cycle times and to save valuable time for the client. Shuttling between Aalborg and the east coast of England, ‘Innovation’ took five sets of monopiles and transition pieces in every single sailing. The project was executed without a single Lost Time Injury (LTI).
GeoSea involved local UK content in the project for the secondary works that were carried out after grouting. A UK project office was established at Grimsby port, and local companies at TeesPort executed vessel preparation, mobilization and demobilization when ‘Innovation’ docked there.