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TWIN X-STERN – Placing the stern both ways

Is a bow really a necessity for large ships? When the vessel’s main function is walk-to-work (W2W) services in the offshore renewable sector, a heightened stern can operate either way, thus facilitating on-site DP positioning. This is the idea behind the TWIN X-STERN™ concept vessel from ULSTEIN, which also includes new thoughts on propulsion, bridge, gangways and cranes.

“The exploitation of renewable energies will become increasingly important in the post-oil era. In the future, renewable energy farms within areas such as solar, wind, wave and current will be established even further from shore in order to maximise the energy created. To serve more distant energy farms, purpose-built walk-to-work vessels with a large amount of accommodation, good motion characteristics and safe transferral will be needed,” says Tore Ulstein, deputy CEO in Ulstein Group. 

Chief designer Øyvind Gjerde Kamsvåg continues: “Take wind turbine farms as an example: the size of coastal wind turbines is limited. By moving the farms further from the shore, the wind turbines can increase in size. The TWIN X-STERN vessels will be ideal for maintaining large-scale wind farming activities far from the shore.” 

“With an X-STERN at each end, the vessel is symmetrical, with a continuous large work deck and cranes on either side 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. Equally important, the accommodation area has the capacity to carry a large number of people. The vessel will be very flexible, as it can perform the same work on either side. The properties of the X-STERN reduce pitching and increase operability in a head sea, and the vessel can keep position with either end towards the wind turbine foundations,” says Kamsvåg.

In this concept, ULSTEIN has been exploring new crane technology, such as the patent-pending ULSTEIN COLIBRI, an electric-driven solution for motion compensation at the crane tip.

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.

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.

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.


Source: Ulstein

Photo: The TWIN X-STERN™ concept also includes new thoughts on propulsion, bridge, gangways and cranes.


June 2015
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