Ship designer Ulstein Design & Solutions is introducing a safer, smarter and more competitive solution for transporting, upending and installing increasingly-large monopiles for the offshore wind industry on Dynamic Positioning (DP).
The patent-pending 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 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. The U-Stern has the appearance of a simple recess in the stern.
Ko Stroo, Product Manager/Lead Naval Architect, Ulstein Design & Solutions said: “But it is much more than that. The shape and location of the recess are finely tuned with CFD and motion analysis to make it work in harmony with the crane and mission equipment.”
More than two years of R&D have enabled a close understanding of how to improve the dynamics associated with DP monopile installation. This has resulted in significant claimed benefits for the U-STERN over ‘traditional’ monopile installation on the side of a vessel:
- Increased operability due to a 25% reduction in motions, excellent wave shielding in the ‘moonbay’ and controlled upending of monopiles;
- 50% 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.
Ulstein Design & Solutions MD Edwin van Leeuwen said: “The idea of longitudinal monopile installation originates in our vast experience in developing heavy lift pipelay vessels with a centreline firing line. 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.”
