The first X-STERN vessel from ULSTEIN. (Photo: SjimpHansen Media)

X-STERN feedback

The X-STERN is the X-BOW® effect implemented in the aft ship. While the traditional transom plate causes slamming and vibrations when the vessel is backing, the pointed X-STERN has no such effect. The softer motions are energy saving and increase comfort and safety.

Market insight from the offshore wind industry shows that 70 % of the vessels operate backwards in-field, despite the slamming experienced with the flat transom plate. The X-STERN hull solution was welcomed and taken in use on service vessels for the offshore wind industry shortly after its introduction in 2015.

Siem Moxie at work next to offshore wind turbine

The SOV crews give various reasons for astern operations:

  • All the work is being performed at the aft. Keeping the aft first leads to a better overview of the vessel’s positioning, as the gangway, the turbine and the ship’s side can all be observed from the bridge.
  • Most power is installed in the aft part of the ship, enabling it to keep positioned more easily.
  • The vessel doesn’t have to turn around before leaving for the next turbine, saving manoeuvering time between turbines.
Acta Auriga at work at the BARD Offshore 1 Offshore Wind Farm.

Crews on X-STERN vessels have additional reasons for operating astern:

  • The X-STERN is kept towards the weather while on standby during night. The service crews get complete rest in between their maintenance shift due to no slamming or vibrations.
  • There will also be no slamming due to the X-STERN while on DP or even when transferring between the turbines.
  • If the weather is not too adverse, the ship stays on the spot with two thrusters running, which leads to substantial reduction in fuel consumption.

The X-STERN met all our expectations. It is amazing to see a vessel going backwards in bad weather without slamming or having spray on deck.

BS Offshore feedback on the 'Windea La Cour'

Proven design - see our references

This new ship is a breath of fresh air. As quiet as a mouse. And so stable! I sleep better in my cabin than I do in an average hotel room. It’s a hotel and an office in one. In short: I’m having a great time here!

Guido de Groot
Planning & Cost Engineer Gemini Offshore Wind, on the 'Windea La Cour'

We are quite convinced that the Acta SX195 vessels will create higher efficiency in offshore logistics operations and thus reduce the overall cost of constructing windfarms and, also, contribute towards a higher uptime of the installed base of offshore wind.

Rob Boer
Managing director at Acta Marine
E book

X-BOW® and X-STERN e-book

Learn more about the key benefits of the X-BOW and X-STERN hull lines. 

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Redefining maritime efficiency

Experience transformative maritime efficiency with Ulstein's designs. We're setting new benchmarks in sustainable seafaring excellence by bridging fuel optimisation with heightened comfort and safety.

Polar Onyx dockhall Marius Beck Dahle


The ULSTEIN X-BOW®, the inverted bow concept, redefined marine engineering. The bow concept was launched in 2005, together with the first shipbuilding contract, and gained immediate interest from shipowners. The X-BOW hull line design has been tried in most weather conditions.

Acta Auriga leaving the construction yard, Ulstein Verft, for her new work base at Eemshaven.


The X-STERN introduces the documented X-BOW® effect to the aft ship, harnessing the benefits of improved safety for crew and equipment, increased flexibility in operations and reduced fuel consumption.

TWIN X-STERN, an ULSTEIN SX222 below view


The TWIN X-STERN® is the latest addition to the innovative designs of X-BOW® and X-STERN® that enhance fuel efficiency and operability. Its unique features distinguish it from others, and its exceptional quality lies beneath the waterline.