Ship design company Ulstein Design & Solutions has designed an offshore wind installation vessel that it says is "a safer, smarter, and more competitive ship design solution for transporting, upending and installing large monopiles on DP."
The patent-pending U-STERN design, according to the company, enables longitudinal storage of monopiles and upending in the ship center line.
"This allows the ship to head into the waves during the installation process, minimizing 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 said.
Ulstein says that the U-STERN looks like a simple recess in the stern, “but it is much more than that,” says Ko Stroo, Product Manager/Lead Naval Architect in 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.”
According to Ulstein, the U-STERN has significant benefits over ‘traditional’ monopile installation on the side of a vessel.
The benefits, per Ulstein, are 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 (Dynamic Positioning) 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 centerline firing line,” says Edwin van Leeuwen, Managing Director in 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 recognizing this as the most viable solution for installing the next-generation monopile foundations.”