The offshore wind industry faces significant installation challenges with the increasing size of monopile foundations. With the patent pending U-Stern, Ulstein Design & Solutions BV introduces a safer, smarter and more competitive solution for transporting, upending and installing large monopiles on dynamic positioning (DP).
The U-Stern enables longitudinal storage of monopiles and upending in the ship centre line. This allows the ship to head into the waves during the installation process, minimising ship motions and fuel consumption, while the U-Stern provides excellent shielding from the waves.
Combining the U-Stern with transverse and longitudinal skidding systems, offshore lifts for monopiles are eliminated, as the main crane is only used to support the upending and lowering of the foundation.
Longitudinal monopile installation
The U-Stern looks like a simple recess. ‘But it is much more than that,’ states Ko Stroo, Product Manager/Lead Naval Architect at Ulstein Design & Solutions BV. ‘The shape and location of the recess are finely tuned with CFD (Computational Fluid Dynamics) and motion analysis to make it work in harmony with the crane and mission equipment.’
The ship designer says more than two years of R&D have enhanced the company’s understanding of how to improve the dynamics associated with DP monopile installation. This has resulted in the U-Stern having significant benefits over “traditional” monopile installation on the side of a vessel:
- Increased operability due to 25 per cent reduction in motions, excellent wave shielding in the “moonbay” and controlled upending of monopiles;
- Fifty per cent power reduction in DP operations due to weather vaning;
- Avoiding port (and offshore) related challenges related to transverse monopile transport and upending;
- Safer lifting operations offshore.
‘The idea of longitudinal monopile installation originates in our vast experience in developing heavy-lift pipelay vessels with a centreline firing line,’ says Edwin van Leeuwen, Managing Director at Ulstein Design & Solutions BV. ‘The U-Stern is, however, not a “one-trick pony”, as the vessel is also suitable for jacket installation and other heavy-lift installation work. In the past months we have presented the U-Stern to major contractors and operators, many recognising this as the most viable solution for installing the next generation monopile foundations.’