Introducing the X-STERN Extender

Oil and gas companies have challenged the maritime industry to come up with ideas for reducing costs in oil and gas exploitation. On the opening day of Nor-Shipping, Ulstein Group presents the X-STERN™ EXTENDER™ concept, a feature which turns a relatively small vessel into a flexible subsea vessel with an extendable moon pool in the aft. This feature increases safety in subsea operations, and the vessel’s smaller size reduces total operational costs and its environmental footprint.

The X-STERN is already an innovation which expands the operational window and offers the captain the choice of placing the stern, rather than the higher and larger bow, towards winds, waves and current when on DP. The newly developed X-STERN EXTENDER feature can be used for conversions as well as newbuilds.
“Ulstein is an innovative company that highly values the demanding challenges that are coming from the oil and gas industry. We appreciate thinking out of the box. Solving challenges such as reducing the costs involved in oil and gas extraction keeps us sharp so that we can advance the maritime industry,” comments Tore Ulstein, Deputy CEO and head of Market and Innovation in Ulstein Group.
“We’ve 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 is not only by allowing it to utilise the stern heading against the weather but also by adding increased scope for operations, for the EXTENDER, when outstretched, also includes a large moon pool. This is a big step when it comes to increasing safety in operations. The vessel can place subsea equipment through the extended moon pool through the use of cranes or an A-frame.”
Hydrodynamic simulations (CFD) in common wave conditions for the North Sea have been carried through. The results show that the water motions inside the moon pool are reduced by 50% compared to outside the moon pool 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 moon pool in the midst 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.
Facts
The X-STERN, introduced in 2014, has evolved from the ULSTEIN X-BOW. The X-BOW idea, launched ten years ago, has become a commercial success. 100 vessels have been ordered to date with this foreship design feature, and the feedback has been very good. X-BOW vessels have a proven ability to maintain speed and schedules even in harsh and head seas, and they can also opt to reduce speed, consequently saving substantial amounts of fuel. The crews have undisturbed rest time due to the gentler movement and absence of slamming. A further consequence is improved safety.
The X-STERN EXTENDER yet another innovative step based on the X-BOW and X-STERN.

Source: Ulstein