From oil and gas to offshore wind


For generations, we have delivered ship designs to service oil and gas installations in the world’s roughest areas. Offshore wind is a new segment in the offshore family, and the knowledge of how the weather can impact the vessel is of great value when developing designs and solutions for offshore renewables.

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Service and assistance vessels
The ‘Windea La Cour’ was among the first of the new breed of service and operation vessels (SOVs) entering the market. Awarded the 'Offshore Renewables Award' in 2017, the 88 metre-long vessel of the ULSTEIN SX175 design is operated by Bernhard Schulte Offshore and was contracted by Siemens Wind Power. She commenced work on the large, 150-turbine Gemini wind farm 85 kilometres offshore the Netherlands in September 2016. Performing wind farm operations, the vessel’s main task is, typically, to transport and accommodate service technicians, and to transfer them safely over to the wind farm installations via her walk-to-work gangway. Her sister vessel, the 'Windea Leibniz', received a contract to service Vattenfall's offshore wind farms Sandbank and DanTysk in the German Bight. A third offshore wind vessel for BS Offshore, the 'WINDEA JULES VERNE' of the ULSTEIN SX195 design, was contracted to work at the Merkur Offshore wind farm.

Construction support
Two vessels of the ULSTEIN SX195 design were contracted by Acta Marine, of which the first, the 'Acta Auriga', was delivered in 2018. The vessel first assignment was to work as an SOV for Ocean Breeze on their BARD Offshore 1 offshore wind farm. The vessel can also work as a construction support vessel (CSV). A part of the requirement was to have the crane and gangway in the centre of the vessel, to increase operational flexibility. The vessel has a motion compensated gangway system with a lift, and a 3D, fully motion compensated, cargo crane capable of lifting 6 tonnes. The sister vessel, Acta Centaurus, was delivered in 2019, and has worked at multiple European Offshore Wind Farms.

Construction in the U.S. possible: Ulstein holds an Approval in Principle (AIP) for its proven Service Operation Vessel (SOV) design, the ULSTEIN SX195, from ABS - the American Bureau of Shipping.

The first X-STERN vessel caused attention
The X-STERN is one of Ulstein’s many innovative contributions to the offshore wind segment. Placing the stern to weather reduces pitch motion and substantially lowers the required power in station keeping compared to bow into the weather.

An intriguing side effect is the ability to keep high backwards speed, increasing the agility of the vessel while operating inside the wind farm. 'Windea La Cour', being the first vessel with an X-STERN, raised attention whilst on sea trials due to her high backwards speed of 12.1 knots, close to the forward speed of 13.95 knots, watch film.

The vessel is very flexible when moving around at the wind farm, and it does not matter where the weather is coming from or where she is heading next. Not less important is the role of the X-STERN in the protection of the cargo on deck. Its sheltered shape protects cargo and crew operating on deck when facing stern seas. The vessel is also carrying the X-BOW, a similar design for the bow. By lowering the acceleration levels of the bow and stern, the design minimises slamming impact. "With the stern towards the weather, we experience absolutely no slamming and vibrations, not even when we are in transfer, and people love it. They get complete rest in between their maintenance shifts," commented the vessel's senior DP operator.

The bow and stern designs improve the sea-keeping abilities and eliminate abrupt stops from head seas. The vessels can easily go either way, and their nimbleness and flexibility make them ideal for working close to the offshore wind farm installations.

First dedicated SOV delivered in 2014
The first dedicated SOV/ISV vessel developed by Ulstein, the ‘Siem Moxie’ (now: Seaway Moxie), delivered 2014 from Fjellstrand, also sported several new features, including Voith Schneider propulsion and a new type of crane with additional capability for installation support. Operated by Seaway Offshore Cables, she has been working as an installation support vessel together with the cable lay vessel ‘Siem Aimery’, now: 'Seaway Aimery.' The pair have set new standards in offshore wind submarine cable installation. The duo has been specifically designed and built to serve the demanding needs for safe and reliable offshore operations in rough seas. 'Seaway Moxie' transports work crews to the platforms and foundations to prepare for submarine cable pull-in and terminations.

The 'Siem Moxie', first dedicated SOV, operating in a Siem duo as an installation support vessel.
The 'Siem Moxie', first dedicated SOV, operating in a Siem duo as an installation support vessel.
The 'Siem Moxie' (now: 'Seaway Moxie'), first dedicated SOV, operating in duo with a cable laying vessel as an installation support vessel.

Equipped with an active heave compensated gangway, the 'Siem Moxie' ('Seaway Moxie') reported more than 14,000 individual connections to offshore structures, transferring in excess of 54,000 personnel from start-up in April 2014 till November 2017, proving her capability as one the most advanced, safe and efficient service operations vessels available in the market.

Installation work and heavy lift crane operations

More and more, offshore wind farms are being built further from shore, and more offshore wind farm work is carried out by monohull vessels, including foundation installation.

Offshore heavy lift vessels are one of the design areas that Ulstein specialises in. Given the trend in the industry for ever bigger wind turbines, larger installation units will be required for both foundations and the wind turbines itself. As early as 2006, Ulstein started developing specialised concepts and presented alternative installation methodologies to the market, like the Floating-to-Fixed (F2F) installation concept and the Windlifter design, which started the industry’s discussion on using monohull vessels for wind farm installations. Floating vessels are seen as the preferred and most effective solution for foundation installation as they make installation faster as it is not restricted by jacking operations. Self-propelled jack-ups are the chosen tool for installing the wind turbines as they provide more precision high up when handling the nacelle and turbine blades.

For the Dutch transportation and installation contractor Jumbo, ULSTEIN developed the entire concept and basic design for a new, LNG powered DP2 Heavy Lift crane vessel. The 'Stella Synergy' will be the largest X-BOW® vessel to date and with its two Huisman mast cranes of 2,500 and 400 tonnes, respectively, will be capable to serve both the offshore wind and the offshore oil and gas industry. To minimise the environmental footprint, the vessel features dual fuel engines, enabling to operate on LNG.

Alfa Lift is OHT's first vessel built specifically for the offshore wind market. The vessel has been designed by the Holland based Ulstein Design & Solutions BV. The heavy lift crane installation vessel with semi-submersible heavy transportation capabilities will be the world’s largest, custom-built vessel for offshore wind foundation installation and will optimise efficiency for the transport and installation of next generation foundations.

The 'Alfa Lift', a dynamically-positioned, 48,000 DWT heavy lift transport and installation vessel for the offshore wind industry. The design combines the benefits of a semi-submersible transport vessel with a large, 3,000 mt lifting capacity main crane. Can perform heavy lift crane operations with the main deck submerged.
The 'Alfa Lift', a dynamically-positioned, 48,000 DWT heavy lift transport and installation vessel for the offshore wind industry. The design combines the benefits of a semi-submersible transport vessel with a large, 3,000 mt lifting capacity main crane. Can perform heavy lift crane operations with the main deck submerged.


As part of Ulstein’s strategy to offer a complete offshore wind vessel portfolio, Ulstein developed the X-JACK series, now also as zero-emission hydrogen powered vessels, as an answer to the offshore wind industry’s need for fit-for-purpose, cost efficient yet future proof wind turbine installation vessels. The design driver is to significantly increase the efficiency compared to existing units in the market, both in logistical lay-out as in pay load capacity, while being lighter at the same time. The combination of an innovative hull shape and vessel layout with well proven jacking and crane technologies from reputable suppliers provides unrivalled heavy lift and cargo capabilities. The X-JACK concept is scalable and include three versions: J101, tailored for maintenance and exchange of wind turbines/nacelles; J102, sized for most optimal and cost effective turbine installation; J103, designed to carry and install six next generation wind turbines to realize even the world’s most remote wind farm locations. Read about the ULSTEIN X-JACK initiative.

Zero-emission wind turbine installation vessel.
Zero-emission wind turbine installation vessel.

Cable laying operations
The LX109 cable lay shipdesign is a high-capacity cable lay vessel with compact dimensions, dedicated for export power cables for the offshore wind industry. Implemented in open top vessel design is the patent-pending ULSTEIN Cable Arch system, which results in a total of 12,500 t of power cable that can be laid as one single piece.

Rock installation services
Ulstein also provides ship designs for subsea rock installation, of which one example is the Van Oord ‘Bravenes’ subsea rock installation vessel, which commenced its first assignment in the North Sea offshore Norway in 2018. Watch animation about the 'Bravenes' functionalities.

This vessel is suitable for installation of a wide range of rock sizes through a fall pipe at the side of the vessel. With a deadweight of 14,000t, a length of 154 metres and a beam of 28 metres, the vessel can operate in water depths of more than 600 metres.

Ulstein has also been contracted by Great Lakes Dredge & Dock to design the first U.S. flagged Jones Act compliant, inclined fallpipe vessel for subsea rock installation. The vessel is critical in building the future of the U.S. offshore wind industry, including establishing a U.S. based rock supply chain network.

Windlifter turbine installation
The Windlifter™ is a system which is designed to transport and (de-)install completely pre-assembled offshore wind turbines – complete with nacelles and blades - in single-lift installation for bottom fixed foundations. The system comprises a storage and handling system for multiple turbines for efficient transport, which is linked to a mechanical system to skid the turbines safely and fully controlled from the vessel onto the foundation. The concept has been designed as a modular system to allow flexible utilisation of available vessels.

In 2015, a customized version was accepted as one of the winner’s in the Statoil (from 2018: Equinor) innovation campaign, the Hywind Installation Challenge. In the Statoil campaign, it was adopted to work with the floating Hywind foundation.