Foundations for the next generation offshore wind turbines will increasingly be installed with floating vessels instead of jack-up vessels. “We have already considered foundations that have never been installed before.”
Wind Energy Magazine – No 4, 2018 – Text Jan Spoelstra
During Offshore Energy 2018, from 22 to 24 October in Amsterdam, Vuyk Engineering Rotterdam presented a new type of crane vessel for the installation of ever larger offshore wind foundations. Very remarkable is the absence of the jack-up legs, used to position a vessel or platform to the seabed. Designs for vessels that float during the installation of wind turbine foundations have already come past. For instance, DEME is building the Orion and Boskalis, with the Boka Lift, also designed by Vuyk, has refitted a semi-submersible heavy cargo vessel for the installation of offshore wind foundations.
Vuyk Engineering Rotterdam, a subsidiary of Royal IHC, regularly makes conceptual designs for offshore companies, and thus has an excellent overview of the installation process for offshore wind turbines. “We expect that in the future, there will be vessels for installing the foundations and separate vessels for the towers, nacelles and turbine blades,” outlines Nicky Mayenburg, senior project manager at Vuyk Engineering Rotterdam. Future offshore wind farms will consist of 12 to 15 MW turbines. “We have already considered foundations that have never been installed before.”
According to Mayenburg, there is a classical catch 22 involved. Wind turbine manufacturers want to install increasingly larger and more efficient wind turbines, but there are not enough vessels available equipped to handle these large installations. “Shipowners that take a vessel such as the one Vuyk proposes here into service, will be actively transforming the playing field forever.” Meanwhile, vessel outfitted with a powerful diesel-electric powertrain and azimuth thrusters, ballast water systems, cranes that can compensate for the heaving waves and grippers that can hold the monopiles of the wind turbines at the correct spot, are very capable to ensure that the foundations for the offshore wind turbines are placed at exactly the right location.
“With this vessel, it is all about the crane,” explains Mayenburg. “It is centrally positioned on the vessel. The vessel is also relatively wide and short, which makes it exceptionally stable by itself. Even when heavy loads are hanging overboard. Moreover, the crane covers the whole deck, therefore it is not necessary to skid heavy constructions. The accommodation and the bridge are built in a special U-shape, thus avoiding their obstructing the crane and creating more deck space to carry even more offshore wind foundations.”
“We do not suggest this vessel is the silver bullet, it is a careful assessment of stability, free deck space and a large crane that covers the whole deck, and we believe this compromise works well when many turbines need to be installed in an area where vessels will have limited mobilization time for turbine installation.”
Vuyk’s new offshore wind installation vessel can transport and install monopiles and transition pieces, tripods as well as jackets. “As a consequence of the increasing water depth, offshore companies will have to transport increasingly heavier foundations,” says Mayenburg. “In less than ten years, a conventional jack-up vessel would propably only be capable of carrying a limited number of foundations on board.”
Is it also possible to install the tower, nacelle and turbine blades without using jack-up vessels? Mayenburg: “There are parties that claim that this is possible, but our view differs. A crane that is towering over hundred metres above the deck and has to install turbine blades on an hub height of possibly 150 metres? We cannot imagine that this will soon be feasible without a jack-up vessel.”