Norwegian shipbuilder and designer Ulstein has introduced what it says is a safer, smarter and more competitive ship design solution for transporting, upending and installing large monopiles on dynamic position (DP).
The U-Stern, developed by its Dutch-based subsidiary Ulstein Design & Solutions, 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. Ulstein explained.
The U-Stern looks like a simple recess in the stern. “But it is much more than that,” said Ko Stroo, product manager and lead naval architect in Ulstein Design & Solutions. “The shape and location of the recess are finely tuned with computational fluid dynamics (CFD) and motion analysis to make it work in harmony with the crane and mission equipment.”
Ulstein said that more than two years of research and development have enhanced its understanding of how to improve the dynamics associated with DP monopile installation, resulting in the U-Stern having significant benefits over ‘traditional’ monopile installation on the side of a vessel. The solution claims increased operability due to a 25% reduction in motions; 50% power reduction in DP; avoiding port and offshore related challenges related to transverse monopile transport and upending and safer lifting operations offshore.
Edwin van Leeuwen, managing director at Ulstein Design & Solutions, added: “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.”
