When the vessel’s main function is walk-to-work (W2W) services in the offshore renewables sector, a heightened stern can operate either way, facilitating on-site DP positioning. This is the idea behind Ulstein's Twin X-Stern concept vessel.
The vessel also includes new thoughts on propulsion, bridge, gangways and cranes. The vessel design was created in response to the ever more distant energy farms. W2W vessels will be needed to transport personnel, need good motion characteristics and offer safe transfers.
X-Stern
The X-Stern on both sides makes the vessel symmetrical, with much deck space and cranes on both sides of the bridge. The X-Stern is heightened by one deck and gives shelter to the deck area. The large deck space can be used for transporting equipment, containers and spare parts. The fact that the vessel can perform the same work on both sides, increases flexibility.
The X-Stern reduces pitching and increases operability in a head sea, and the ship can stay in position with either end towards the wind turbine foundations.
Ulstein Colibri
In this concept, Ulstein has also been exploring new crane technology, such as the patent-pending Ulstein Colibri, an electric-driven solution for motion compensation at the crane tip.
Propulsion
The vessel is equipped with a powerful, azimuthing rim-driven counter-rotating twin-propeller propulsion unit with variable nozzle geometry at each end. The vessel can head into open water in harsh weather while maintaining gentle, comfortable movements for the crew’s well-being. The two smaller main propulsion units provide the same power as one large unit, but with increased fuel-efficiency. Operations are optimised as the captain can vary between transit modes and high-thrust modes.
Gangways
The vessel can be equipped with a safe transferral ramp on both the star board and port side of the bridge. Additionally, a large W2W ramp for oil and gas rigs can be integrated into the vessel for more flexibility.
Bridge
The asymmetrical bridge can be made of composite material and is placed midship, diagonally above the work deck. The operating bridge is placed as a lookout platform on both the starboard and port sides, close to the ramp on either side, giving a full overview of the nearest ramp as well as the complete work deck area. The helideck is placed on top of the bridge, where the movements are at the lowest.
