The X-STERN® introduces the documented X-BOW® effect to the aft ship. The sloping, higher stern allows for a sharp stern shape in which the transom plate is replaced by a pointed aft. Some of the benefits are: Improved safety for crew and equipment, increased flexibility in operations and reduced fuel consumption.

For vessels where the best possible operational characteristics are vital, the Captain’s first choice will be to place the X-STERN® towards the weather instead of the bow. When placing the stern towards the weather, the X-STERN® has a major effect on the vessel’s capabilities and flexibility. Stern first, the vessel will be less influenced by weather, and pitch motion and wave drift will be reduced. The aft working sector increases. The work deck aft is enclosed, with no sea on deck or ice build-up and increased safety for crew, cargo and equipment. Deeper drafts increase the benefits.

The advantages include:

  • Reduced pitch motion and increased operational window when placing stern to weather (weather vaning). 
  • Up to 50% less propulsion power required with stern to weather vs bow to weather
  • Significant reduction in wave response and slamming. Stern is quartering seas, which decreases accelerations and improves comfort
  • Safer workplace due to sheltered aft deck and high freeboard, less probablility of green water on deck
  • Reduction in resistance in calm water and waves by up to 28%
  • The option to sail astern and with up to 60% reduction in power consumption
  • Massive reduction in trim and draft sensitivity

The X-STERN is a natural evolvement of the X-BOW®, and the first deliveries (2016/2017) are for two service operation vessels for the offshore wind industry.

"The X-STERN met all our expectations. It is amazing to see a vessel going backwards in bad weather without slamming and having spray on deck." 
'Windea La Cour', BS Offshore

Why is backing preferred in SOVs?

Operational feedback shows that SOV crews choose to operate the vessels in astern mode while in-field. The 'aft first' experience is improved with the X-STERN, which has been introduced to several offshore wind service ships.

Backing preferred

CFD simulations

CFD simulations have been carried out. The promising results from these analyses were proved in real-life conditions when the first X-STERN vessel, the Windea la Cour, was tested during sea trial in June 2016. Read more.

Seatrial of the Windea La Cour - first real-life X-STERN test
Seatrial of the Windea La Cour - first real-life X-STERN test

Improved positioning

The X-STERN pointed shape improves positioning capabilities compared to stern designs with a flat transom plate.

Reduced weather dependency

Improved motion characteristics widens the operational window.

Fuel efficiency

Vessels can operate in a wider sector with the same power consumption. Reduced fuel emissions improves the vessel's footprint.



The X-STERN EXTENDER™ concept is a feature which turns a relatively small vessel into a flexible subsea vessel with an extendable moon pool in the aft.


TWIN X-STERN™ for walk-to-work services

Is a bow really a necessity for large ships? A heightened stern, the TWIN X-STERN™, can operate either way, thus facilitating on-site DP positioning. This idea was nominated for the Innovation of the Year Award at the OSJ Conference 2016.



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 all weather conditions.