Two sterns, no bow

Tuesday, 9 June, 2015 - 10:30
“The Twin X-Stern vessels will be ideal for maintaining large-scale wind farming activities far from the shore,” says Chief Designer Øyvind Gjerde Kamsvåg. (Graphic: Ulstein)
“The Twin X-Stern vessels will be ideal for maintaining large-scale wind farming activities far from the shore,” says Chief Designer Øyvind Gjerde Kamsvåg. (Graphic: Ulstein)

Two sterns, no bow – this is the main characteristic of Ulstein’s new Twin X-Stern concept. But it also includes new thoughts on propulsion, bridge, gangways and cranes.

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.

“The exploitation of renewable energies will become increasingly important in the post-oil era. 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: “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 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 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 turbines.”

The Twin X-Stern vessel is equipped with a powerful, azimuthing rim-driven counter-rotating twin-propeller propulsion unit with variable nozzle geometry at each end. According to Ulstein, the two smaller main propulsion units provide the same power as one large unit but with increased fuel-efficiency. The vessel can be equipped with a safe transferral ramp on both the star board and port side of the 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.

In this concept, Ulstein has also been exploring new crane technology, such as the patent-pending Colibri crane add-on, a 3D motion-compensated handling system for the purpose of increasing vessel operability. This compact crane add-on system can be mounted on standard cranes, whether new or existing. A full scale prototype with a capacity of 2.5 mT is under development. 3D motion-compensation technology is not new to the industry and has enabled greater operability for personnel transfer between vessels and fixed offshore platforms through the use of motion-compensated gangways. The next natural step in increased operability is therefore motion-compensated lifting to match the increased operability offered by compensated gangways.

Katharina Garus

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