Dipl.-Ing. Guido Schulte, Dipl.-Ing. Stefan Hadeler, Nordic Yards Wismar GmbH, Wismar
The installation technology and philosophy of recent offshore wind projects is based on the experiences gathered from the offshore oil and gas industry. However, the available fleet of installation vessels with its oil and gas driven charter rates is not always best suited for the serial production character of the future offshore wind farm installation. Nordic Yards has worked extensively on several wind installation vessel projects over the last couple of years, thereby obtaining deep insight into the particular boundary conditions and objectives of this field. Nordic Yards now comes up with an own concept that tackles the main challenges in an innovative way. The newly developed “Nordic Heavy Installer” indeed constitutes an original concept for the windmill erection task. At the same time, it embodies a new combination of well-proven single design elements. The major uncertainty of all logistic concepts for offshore wind installation is the downtime due to environmental conditions. Current technologies and most concepts are based on the sequential installation of single components and require calm weather conditions for the assembly process. Another key aspect is the supply of material. In general, two philosophies are predominant: on the one hand the feeder concepts, where an installation vessel, mostly a jack-up rig, is working in the field while supply vessels deliver the single components in a shuttle service. The second principal approach is the combination of an offshore assembly, installation and supply vessel in one unit. It shuttles all single elements between a hub port and the offshore windmill park and performs the whole assembly offshore, which makes it vulnerable in terms of environmental conditions, in particular the (cantilever-type) crane operations in high winds do limit the assembly window. Due to the high required displacement of such units and the integration of a suitable jacking system in combination with requirements of cargo deck layout, the underwater geometry of those vessels can only be a compromise, leading to an excessive hull resistance and high operational costs. The philosophy behind the “Nordic Heavy Installer” is to reduce the amount of offshore construction work to a minimum and to shift most of it to onshore facilities. Therefore the tower, nacelle, hub and blades are assembled and pre-tested in harbour in whole. Only the interface between tower and foundation has to be connected offshore. Furthermore, the vessel’s intention is to cover the complete logistic chain: starting from efficient foundation installation for pre- and post-piling structures up to the final assembly of the wind turbine. The hull is designed for best sea keeping behaviour and low resistance. A twin shaft line FPP propulsion in combination with high efficient rudders and transverse tunnel thrusters enables the vessel to sail in harsh conditions with the most unfavourable loading case as well as to fulfil the requirements of dynamic positioning operation. The jack-up system with its spud cans is arranged above the water line to eliminate the increase of resistance in transit. Cargo handling is realised by an integrated gantry crane running on the vessel’s sides. With the help of intensive research and application of enhanced numerical calculation methods, the sea keeping behaviour of the vessel has been optimised to fulfil the strict requirements of wind turbine manufacturers with special respect to the max. accelerations acting on the single components.