In ship design, an inverted bow (occasionally also referred to as reverse bow) is a ship's or large boat's bow whose farthest forward point is not at the top. The result may somewhat resemble a submarine's bow. Inverted bows maximize the length of waterline and hence the hull speed, and have often better hydrodynamic drag than ordinary bows. On the other hand, they have very little reserve buoyancy and tend to dive under waves instead of piercing or going over them.
Inverted bows were popular on battleships and large cruisers in the early 20th century. They fell out of favour, as they were very wet at high speeds and in heavy seas, but have made a comeback on modern ship design.
The Ulstein X-Bow (or just X-BOW) is an inverted ship's bow designed by Ulstein Group to improve handling in rough seas, and to lower fuel consumption by causing less hydrodynamic drag. It is shaped somewhat like a submarine's bow.
The MV Bourbon Orca, design AX104, is an Ulstein A-Series anchor handling tug supply vessel (AHTS) built for Bourbon Offshore Norway, the Norwegian division of the French Groupe Bourbon, and was the first ship built with the Ulstein X-bow in 2006. She was awarded Ship of the Year 2006, both by Skipsrevyen and Offshore Support Journal. In 2007, the Bourbon Orca design model was included in the London Science Museum's display of innovative technology. The vessel's operator claims that the design achieves higher speed and a calmer motion in head, rough seas.
The Ulstein Verft yard has also constructed two vessels featuring the X-Stern, a similar shape for the stern, these two vessels being offshore wind power service vessels for Siemens Wind Power. In 2015, the X-STERN was awarded the Next Generation Ship Award. The first of the two ships, is servicing the Gemini offshore wind farm.