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.

The X-BOW (and later, the X-STERN) is one of ULSTEIN's main contributions to maritime history. X-BOW vessels are being built at shipyards on many continents. Currently, more than 100 vessels with this bow concept are being constructed or in operational work around the world.

Acta Auriga on sea trial
The Acta Auriga on sea trial, March 2018. The vessel is custom-made for the offshore renewables industry.

The X-BOW introduces the gentle displacer; a tapered fore ship shape with a different volume distribution as well as sectional angles, resulting in a wave piercing effect at small wave heights, and also reduces pitching and bow impact loads in bigger seas. When comparing fore ship volumes with more conventional, bulbous bow shapes, the X-BOW has more displacement volume starting from the waterline.

The experience is quite amazing. I cannot imagine myself ever travelling with a conventional bow vessel again in winter time. Captain of the AHTS 'Bourbon Orca​'

Instead of just rising on the waves and then dropping with colossal force, the X-BOW® is able to absorb the force more consistently across its surface – enabling the ship to remain more stable during poor weather conditions, increasing comfort for passengers and crew alike. And because it uses less fuel to get through the waves, it also helps to save energy.

Accepts anything the sea throws at it

The X-BOW is in its right element when in the more harsh environments. The benefit is the security for the crew, passengers and ship that the bow can accept anything the sea throws at it. This becomes stories, remembered and told by the crew and passengers on these vessels, and this is where the X-BOW design excels.

From a Health, Safety & Environment (HSE) point of view, reduced accelerations and slamming forces mean less wear and tear on people and equipment. The X-BOW has very little spray, so the deck remains dry behind. It takes very little water on deck to start being a hazard, or simply a nuisance.

Major benefits of the X-BOW

  • Improved power efficiency
  • Soft entry in waves
  • Very low levels of noise and vibrations
  • Reduced bow impact and slamming
  • Reduced wave-induced vibrations
  • Improved resting time
  • Lower acceleration levels
  • Lower pitch response due to volume
  • More comfortable on board conditions
  • Lower speed loss
The subsea vessel 'Seven Viking' in North Sea weather, photo: Christian Romberg.

Statements from X-BOW users

With feedback like ‘amazing experience’ and’ 'I’ll never again work on any other type of vessel in winter’ being stated by crews on X-BOW® vessels, it is hard to ignore the impact this hull innovation has had since it first appeared in 2005.

Real life stories

The X-BOW® experience

The X-BOW® makes a huge difference in sea behaviour. The X-BOW® splits the wave energy and reduces the slamming impact. Successfully proven in more than 100 ships, the hull shape is about to become a game changer for expedition cruising.

Jump into the adventure!

Improved power efficiency

Reducing pitch/heave accelerations and speed loss in waves, which renders higher transit speed or reduced power consumption possible. This improves fuel efficiency and reduces emissions to air.

Increased comfort

Eliminating slamming and bow impact, thereby reducing noise and vibration. This leads to a more comfortable workplace and more effective rest time for the crew and passengers.

Safety & less damage

Soft entry in waves, thus reducing spray and icing. The likelihood of extreme weather damage to the forebody is reduced.

X-BOW - how it started

​When times are tough, it is still possible to nurture and grow good ideas. That’s the story behind the ULSTEIN X-BOW® hull line design, which upon its introduction in 2005 literally turned the image of the ship’s bow upside down.

The development of the X-BOW

Simplified shipbuilding

When presenting the X-BOW® design in 2005, the designers claimed that these vessels would be easier and less resource intensive to build. In 2006, this statement was tested in reality through the construction of an X-BOW® hull at Maritim Ltd: "It was easier to build the backward-sloping bow than a conventional bow."

Simplified shipbuilding

The X-BOW inspires artists

The X-BOW has inspired various artists, from bank note and stamp illustrators, to church architects and animators.

The X-BOW inspires

Surfing on top of the waves

The X-BOW® is somewhat the reverse of a conventional bow, leaning backwards instead of forwards. An X-BOW vessel cleaves the waves, significantly reducing noise and vibration. She can sail faster and consume less fuel in high waves than a conventional bow would allow. And she is more comfortable for the crew.

Organic lines


When new hull designs are undergoing tank tests, a scale model must endure various waves and wave length conditions. We have performed model tests and comparative model tests for X-BOW hulls and bulbous bows in areas such as supply, seismic, offshore construction, drill, short-sea and anchor handling tug supply.


More films:

X-BOW and X-STERN: Studies, documentation and experiences

X-BOW whitepaper
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