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    Ulstein introduces X-STERN Extender

    Vessel & ROV News // June 5, 2015

    The X-STERN Extender can turn a vessel into a subsea vessel.

    Ulstein Group in Norway used the 2015 Nor-Shipping exhibiton to unveil the X-STERN EXTENDER concept, a feature which turns a relatively small vessel into a flexible subsea vessel with an extendable moonpool in the aft.

    The company believes that this feature increases safety in subsea operations, and the vessel’s smaller size reduces total operational costs and its environmental footprint.

    The newly developed X-STERN EXTENDER feature can be used for conversions as well as newbuilds.

    Ulstein's Deputy CEO and head of market and innovation, Tore Ulstein, said: "We have now taken development of the X-STERN even further, into a conceptual study where we’re exploring an extendable X-STERN.

    "The feature widens the vessel’s operational window. This not only allows it to utilise the stern heading against the weather but by adds to a vessel's scope for operations. The EXTENDER, when outstretched, also includes a large moonpool. The vessel can place subsea equipment through the extended moonpool through the use of cranes or an A-frame.”

    Ulstein has carried out hydrodynamic simulations (CFD) in common wave conditions for the North Sea. The results show that water motions inside the moonpool are reduced by 50 per cent compared to outside the moonpool and guarantee a safety margin against green water.

    “We believe this is a much better solution than working over the ship’s side, which can be a risky and strongly weather-dependent operation. Even for a subsea vessel that normally has a moonpool in the middle of the ship, valuable central deck space and hull volume will be freed up with the moon pool placed aft.

    “The X-STERN EXTENDER is an add-on; it is not part of the ship’s structure and not counted in the ship’s length. This is important when it comes to cutting costs. The deadweight, fuel consumption and operational costs for a fully functional subsea vessel will be reduced. In addition to these operational aspects, there are the central characteristics of the X-STERN: an aft deck protected from weather, extra volume and smoother motions."

    Ulstein introduced the X-STERN in 2014. It evolved from the ULSTEIN X-BOW, which was launched ten years ago, and has since has become a commercial success.



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