Table of contents:
This is the second part of our story about a new type of vessel: the Offshore Wind Farm Service Vessel. Service Operation Vessels (SOVs) play a vital role in the successful operation and maintenance of offshore wind farms in the North Sea, one of the world's most active and ambitious regions for renewable energy development. As offshore wind farms grow in size and move further from shore, the demand for specialised vessels that can provide safe, efficient, and continuous support to wind turbine technicians and equipment has increased significantly. Offshore wind support vessels have become indispensable in bridging the logistical gap between shore bases and offshore installations, enabling a reliable presence at sea for extended periods.
The North Sea, known for its harsh weather and challenging marine conditions, presents unique logistical and operational challenges. Traditional crew transfer vessels (CTVs), which shuttle technicians to wind turbines daily, are no longer sufficient for large-scale, deepwater projects. SOVs offer a more robust solution, providing accommodation, workshops, storage facilities, and advanced dynamic positioning systems that allow them to stay offshore for weeks at a time. This capability significantly reduces weather-related downtime and increases the availability of turbines for maintenance, directly impacting wind farm productivity and profitability.
From an operational standpoint, Offshore wind support vessels enhance safety and efficiency. They are equipped with motion-compensated gangways that allow technicians to walk directly from the vessel to the turbine platform, even in high seas (see also: Walk-to-work offshore 101). This eliminates the need for dangerous step transfers and enables work to continue under a wider range of conditions. SOVs also serve as mobile bases, reducing travel time to individual turbines and allowing for better planning and coordination of maintenance activities. This continuous offshore presence leads to faster response times in the event of technical issues, supporting the overall reliability of the energy supply.
The strategic importance of SOVs is also evident in the energy transition agenda of countries surrounding the North Sea, such as the United Kingdom, Germany, the Netherlands, and Denmark. These nations are investing heavily in offshore wind as a core pillar of their decarbonisation strategies. SOVs are not only a critical enabler of this transition but also represent an opportunity for innovation, local employment, and maritime sector growth. Many shipbuilders, equipment manufacturers, and technology providers are increasingly focusing on this niche segment, developing new generations of SOVs with hybrid propulsion systems, digital monitoring tools, and enhanced crew welfare facilities.
In essence, Service Operation Vessels are the backbone of offshore wind farm operations in the North Sea. Their ability to maintain a permanent offshore presence, withstand adverse conditions, and support the complex logistics of wind farm servicing makes them an essential part of the offshore energy infrastructure. As the scale and complexity of wind farms continue to grow, the role of SOVs will become even more central, not only in sustaining renewable energy production but also in shaping the future of maritime operations and sustainable engineering in the region.
Now, let's have a look at three landmark SOVs in the history of the North Sea.
It's the first offshore service operation vessel built at Havyard Ship Technology's shipyard in Leirvik, Sogn in Norway using the Havyard 832 design. Esvagt ordered two vessels in July 2013. The vessel was christened and delivered to its owner in February 2015. Esvagt Faraday, its sister ship, also arrived in February 2015. It's been chartered for five years to transport cargo and crew to and from the Baltic II offshore wind farm by Siemens Energy. A third Havyard 832 SOV was ordered in December 2014 for operations at the Dudgeon wind farm, developed by Statoil and Statkraft off the coast of Norfolk, UK. It was delivered in August 2016.
With a length of 83.7m, a moulded breadth of 17.6m, and a maximum draught of 6.5m, it's designed and engineered by Havyard Design & Solutions. Its deadweight is roughly 4,200 tons at max draught. Gross tonnage is 5,006 tons and net tonnage capacity is 1,502 tons. Esvagt Froude can carry cargo up to 2,500 tons. On deck, the SOV has 450m2 for workshop space and six 20ft containers for spare parts. In its cargo deck, you can store 20ft containers with spare parts for wind turbines. 1,100m3 fuel, 250m3 base oil, 800m3 freshwater, 2,500m3 water ballast, 2,500m3 drilling water, 300m3 dry bulk, 1,025m3 mud, 1,025m3 brine, 1,560m3 oil recovered and 150m3 low flashpoint liquids can fit in the vessel. For Fred Olsen Windcarrier, Brave Tern is a heavy-lift jack-up ship.
In Esvagt Froude, technicians can get to wind turbines with a hydraulically stabilised asymmetric bridge, even during 2.5m waves. There's a roll-damping system onboard, so you're comfortable, and it's easy to use the gangway. During the servicing of wind farms, the dynamic positioning system provides better manoeuvrability. The vessel can be placed close to the wind turbines for easy and safe operations. In addition to a high ERN score (station-keeping capability), the Froude is equipped with a deck crane that can lift 2 tons at a distance of 12 meters.
There's also an incinerator and compactor to manage waste, and closed-circuit TV to monitor the vessel and the central area. A-Lifting delivered a crane package for Esvagt Froude and Esvagt Faraday. Havyard Power & Systems did the electrical engineering, automation, and alarm systems, including the Havyard Concept Bridge.
Esvagt Froude has 60 single-bed cabins for 40 technicians and 20 crew members. The superstructure houses accommodation, meeting rooms, fitness areas, and entertainment areas.
It has an open STB model 7B that accommodates two crew members, three technicians, and their equipment, along with the Walk-to-Work gangway system. The STB system was developed at Esvagt headquarters in Esbjerg. It also has an enclosed STB model 12A carrying two crew members and eight technicians, along with one ton of cargo. A fast rescue boat from Esvagt is on top.
The vessel is powered by an advanced DC power system and a diesel-electric propulsion system developed by Siemens in Trondheim, Norway. Besides being fuel-efficient and energy-efficient, Esvagt Froude is equipped with Siemens Blue Drive propulsion, which cuts fuel and greenhouse gas emissions. It has four diesel generators that each generate 1,650kW. There are also 1,600kW main azimuth thrusters and a 700kW forward thruster. The ship can go 14.5 knots.
Edda Passat, operated by Østensjø Rederi, was delivered in 2018 by the renowned builder Astilleros Gondán. This vessel carries the Norwegian International Ship Register (NIS) flag with Haugesund as its port of registry and is distinctly recognised by its call sign LALZ8. Spanning a length of 82 meters, a breadth of 17 meters, and a draft of 5.40 meters, these vessels are designed to handle a deck capacity of 5 tonnes per square meter over a significant deck area of 360 square meters. The accommodation facilities are notably comprehensive, offering 58 single cabins and two double cabins to house a total of 60 personnel on board, alongside three offices, a meeting room, and a hospital/sick bay. For crew welfare, amenities include a gym, a day room, and a game room, ensuring a comfortable stay during offshore operations.
The vessel is equipped with advanced offshore logistics capabilities, featuring a Uptime 23.4 m 3D compensating gangway and an SMST 1T 3D crane with a lifting capacity of up to 2.0 tonnes. Although they lack a helideck, they provide boat landing facilities at the aft and starboard sides, and their propulsion system includes 2 Rolls-Royce Azimuth thrusters and 3 Rolls-Royce Tunnel thrusters, ensuring precise manoeuvrability and stability in challenging sea conditions. Their fuel system is designed for both Marine Gas Oil (MGO) and Marine Diesel Oil (MDO), reflecting flexibility and efficiency in operations.
Edda Passat, together with her twin sister Edda Mistral, is really important for running Ørsted's offshore wind farms. Both have a Uptime 23.4 m 3D compensating walk-to-work system, so you can get on and off wind turbines easily, and they play a big role in maintaining offshore wind farms.
The vessel, delivered on 28 February 2017 and officially named at Ulstein Verft on 2 March by its lady sponsor Dai Ling, courtesy of ICBC Leasing, carries yard number 310 and represents the 100th implementation of Ulstein Group's innovative X-BOW hull line design. It features the advanced X-STERN solution, enhancing comfort and reducing noise and vibrations when manoeuvring backwards between turbines at wind farms. This technology was a key factor in the vessel being nominated for the 2017 Ship of the Year Award.
Designed as an SOV, it significantly boosts the efficiency of service operations at offshore wind farms by offering a reliable and environmentally friendly platform for operations and maintenance support, technician accommodation and transport, and providing safe and reliable access to offshore installations. The vessel is named in honour of the German mathematician, philosopher, and physicist Gottfried Wilhelm von Leibniz, who proposed the use of wind power for operating pumps in the 17th century. It embarked on its inaugural assignment with Siemens Wind Power in April 2017, servicing Vattenfall's offshore wind farms Sandbank and DanTysk located in the German Bight.
Undergoing an upgrade from SOV to a Commissioning Service Operation Vessel (CSOV) between 31 October 2022 and 4 February 2023 at Ulstein Verft, the vessel saw its cabin capacity increase from 60 to over 80. This upgrade included the installation of an additional pedestal on the stern to facilitate operations in the Baltic Sea, augmenting the existing North Sea pedestal. Its primary specifications are an 88-meter length, 18-meter beam, 3150 tonnes deadweight, a maximum draught of 6.4 meters, and a top speed of 13.5 knots. The vessel offers a deck area of 380 square meters. It has fuel oil, fresh water, and ballast water capacities of 1150, 1200, and 2400 cubic meters, respectively.
Want to learn more about other SOVs? Wait for our next blog post or
order our SOV book for free.
A Service Operation Vessel (SOV) is a purpose-built ship designed to support the installation, maintenance, and operation of offshore wind farms. It serves as a floating base for technicians, offering accommodation, workshops, storage, and advanced navigation systems to remain stable and positioned near wind turbines for extended periods.
Modern SOVs use Dynamic Positioning (DP) systems that rely on GPS, sensors, and thrusters to automatically maintain a fixed position and heading, even in rough sea conditions. This allows safe transfer of personnel and cargo to and from wind turbines without anchoring.
Safety is a top priority on SOVs. Electronic Personnel on Board (e-POB) systems track who is on the vessel in real time. e-Mustering digitises emergency drills and responses, ensuring everyone is accounted for quickly. Access Management controls who can enter critical areas, helping prevent accidents and unauthorised entry.
Service Operation Vessels have become indispensable in the offshore wind industry, evolving from simple support craft into high-tech platforms designed for complex, long-duration missions. Their advanced propulsion, navigation, and connectivity systems ensure efficiency in even the most demanding sea conditions. Just as crucial is the focus on safety: modern SOVs integrate electronic Personnel on Board (e-POB) systems, digital mustering, and controlled access management. These technologies provide real-time crew tracking, streamline emergency response, and enhance operational security—making today's offshore operations not only more efficient but also significantly safer for everyone on board.
Delve deeper into one of our core topics: Personnel on board
Deep-sea operations refer to industrial activities conducted far from shore, typically at ocean depths greater than 200 meters. These operations include offshore drilling, wind farm construction, subsea cable installation, and marine research. They require specialised vessels, equipment, and technologies to withstand high pressure, strong currents, and remote conditions. Deep-sea operations are critical for energy production and infrastructure but also raise environmental and safety concerns.
References
(1) M. Buzinkay & M. Wozniakowski-Zehenter (2025): The Journey. Life and Work on a SOV.
(2) Jahn, F., Cook, M., & Graham, M. (2008). Hydrocarbon Exploration and Production. Elsevier.
Note:
This article was partly created with the assistance of artificial intelligence to support drafting. The head image was generated by AI.