Built by Tersan Shipyard in Türkiye, the DP2 walk-to-work vessel is purpose-designed for offshore wind construction and maintenance. The TWIN X-STERN solution, with main propulsion units at both ends, offers high operability, reduced motion, and efficient station-keeping in demanding conditions.
Following mobilisation, Acta Gemini will commence a long-term charter at the Sofia offshore wind farm on Dogger Bank in the UK. Operating from Grimsby, the vessel will deliver offshore accommodation and walk-to-work services in support of operations and maintenance on behalf of RWE, according to Acta Marine.
With sister vessels Acta Pegasus and Acta Hercules already delivered, the newbuild series strengthens Acta Marine’s modern, future-ready fleet supporting Europe’s energy transition.
Acta Gemini continues the collaboration between Acta Marine, Tersan Shipyard and Ulstein, combining advanced vessel design with a strong focus on safety, efficiency and crew and client comfort for offshore wind operations.
CSOV/SOV/W2W
CSOV/SOV/Walk-to-Work vessels for offshore wind and oil and gas.
Keep your offshore operations safe, efficient, and on schedule with proven offshore vessels.Acta Gemini
Construction Service Operation Vessel (CSOV) for the Offshore Wind Industry. The ULSTEIN TWIN X-STERN® has several characteristics, as a ship with two sterns and four main propeller units: two at each end.
Acta Pegasus delivered to Acta Marine: Ulstein design supports sustainable offshore wind operations
Acta Pegasus was delivered to Acta Marine in December 2025 by Tersan Shipyard. This vessel is the first of four newbuild Walk-to-Work (W2W) Construction Service Operation Vessels (CSOVs) designed by Ulstein Design & Solutions AS for Acta Marine.
Frequently Asked Questions (FAQs)
CSOV stands for commissioning service operation vessel. It is a purpose-built ship designed to support offshore wind farm construction, commissioning and maintenance. CSOVs act as floating bases where technicians live and work during extended offshore missions. They are equipped with motion-compensated gangways, cranes and dynamic positioning systems to carry out safe operations in demanding sea conditions.
Walk-to-Work means personnel can walk directly from the vessel to an offshore structure, such as a wind turbine, using a motion-compensated gangway. Before this technology, technicians relied on small craft and had to climb ladders, which was limited by wave height. Walk-to-work gangways allow transfers in rougher seas, adding weeks or even months of operational time each year. It is safer, faster and more efficient.
A motion-compensated gangway is a stabilised bridge mounted on a vessel that connects to an offshore structure such as a wind turbine. Sensors continuously measure the vessel's movement in all directions. Hydraulic or electric actuators then adjust the gangway in real time to cancel out that movement, keeping the gangway tip steady against the fixed structure. This allows personnel to walk safely between the vessel and the turbine.
Safe Walk-to-Work transfers depend on the vessel holding a precise position next to a wind turbine. Even small movements can compromise the gangway connection and put personnel at risk. DP allows the vessel to remain stable within a few metres of the target, regardless of changing weather. Without reliable DP, walk-to-work operations would not be possible in the conditions typically found at offshore wind farms.
Dynamic positioning (DP) is a computer-controlled system that automatically holds a vessel in position using its own thrusters. Sensors such as GPS, gyrocompasses and wind sensors feed real-time data to a control computer. The computer then calculates the thrust needed to counteract wind, waves and current, keeping the vessel exactly where it needs to be. Think of it as autopilot, but instead of steering a course, it keeps the ship still.
The TWIN X-STERN is Ulstein's patented hull design. Its symmetric hull shape behaves more efficiently in harsh weather conditions. Four azimuth thrusters, two at each end, increase the manouverability. The azimuths have higher efficiency by being capable of turning the thrust directly in the direction of the waves and current. The combination of thrusters and hull design result in lower energy consumption and reduced motions, and therefore higher operability and comfort.
Ulstein has designed or redesigned 22 walk-to-work vessels to date, of which 16 are currently in operation. These vessels collectively service more than 5,000 turbines every year, with over 95,000 gangway connections annually. Ulstein was one of the first movers in this segment, starting with the Seaway Moxie, delivered in 2014.
TWIN X-STERN E-book
In the e-book you can dive into topics such as:
- What is the ULSTEIN TWIN X-STERN?
- How does it work?
- What are the application areas?
And much more.
