Applying a Needs Analysis to promote Daughter Craft for year-round access to far-offshore wind turbines

Abstract

New offshore wind farms are moving farther away from the shore; to locations characterised by adverse weather conditions. This challenges current maintenance strategies because, besides being further from shore, far-offshore wind turbines need more frequent maintenance and must be accessed in rougher weather conditions. Service Operation Vessels provide high accessibility to far-offshore wind turbines, but they lack multitasking capabilities. Its daughter craft is a valuable asset for unplanned maintenance in the summer when it can operate safely, but it is often not deployable during the winter due to the rougher weather conditions. The main research question is: What are the deficiencies of current DCs, and how can these access vessels be modified to operate year-round at far-offshore wind farms? The results show that the current DC’s deficiencies lie in its current operational requirements. Also, performance in oblique waves is currently riskiest since that is when there are higher vertical accelerations or a combination of vertical and lateral accelerations. Furthermore, wave steepness has significantly more effect on accelerations that wave height. Lastly, future DC designs should be focussed on stable seakeeping performance during transfers rather than high-speed transit. An analysis into the seakeeping performance of four prototypes showed that it is feasible to increase the transfer requirement from Hs ≤ 1.5 m to 2.0 m ≤ Hs ≤ 2.5 m. The catamaran type DCs have a high potential to realise year-round accessibility to far-offshore wind farms due to their resulting performance in oblique waves.