CSOV & SOV vessel design for walk-to-work operations…

Built for demanding offshore operations

Our CSOV and SOV vessels support construction, maintenance and operations across offshore wind and oil and gas projects.

Designed for owners who need to deliver from day one

You need a vessel that works from the first charter. Ulstein has designed walk-to-work vessels for Olympic, Acta Marine, Bernhard Schulte Offshore, Siem Offshore, NYK Line and Shanghai Electric Windpower Group

We guide you from concept to delivery:

Proven vessel designs adapted to your project
Build options in Norway or through our global shipyard network
Support from experienced offshore specialists

Designed for performance and efficiency

Our vessels are built for safe and stable operations:

Motion-compensated gangway systems for safe personnel transfer
Proven X-BOW®, X-STERN®, and TWIN X-STERN® hull designs for better seakeeping
High accommodation capacity and onboard comfort
Hybrid propulsion and energy storage for lower fuel consumption
Prepared for alternative fuels and reduced emissions
Close to 50% lower fuel consumption and emissions for Olympic’s TWIN X-STERN® CSOV newbuilds

Reduce risk and improve uptime

With Ulstein-designed CSOV/SOVs, you can:

Maintain safe access to offshore installations
Keep operations running in harsh weather
Reduce fuel consumption and emissions
Improve efficiency across offshore wind and oil and gas

What is the difference between crew transfer vessel (CTV), service operation vessel (SOV), commissioning service operation vessel (CSOV) and accommodation support vessel (ASV)?

Vessel type	Main activities	Accommodation	Crane capacity	Deck area	Transferring technology	Wave conditions
CTV	Long-term operation and maintenance (O&M) contracts of windfarms	8 to 50 POB	Up to 5 tonnes	5 to 200 m2	No gangway	Up to 1.5 m Hs
SOV	Long-term operation and maintenance (O&M) contracts of windfarms	40 to 100 POB	2 to 20 tonnes	200 to 500 m2	Gangway Type 1	Up to 2.5 m Hs
CSOV	Short term O&M contracts and commissioning contracts for windfarms or O&G projects	90 to 140 POB	5 to 50 tonnes	400 to 800 m2	Gangway Type 1 or 2	Up to 3.5 m Hs
ASV	Short term commissioning contracts for windfarms or O&G projects	100 to 150 POB	100 to 150 tonnes	500 to 1200 m2	Gangway Type 1 or 2	Up to 3.5 m Hs

Vessel type

CTV

Main activities

Long-term operation and maintenance (O&M) contracts of windfarms

Accommodation

8 to 50 POB

Crane capacity

Up to 5 tonnes

Deck area

5 to 200 m2

Transferring technology

No gangway

Wave conditions

Up to 1.5 m Hs

Vessel type

SOV

Main activities

Long-term operation and maintenance (O&M) contracts of windfarms

Accommodation

40 to 100 POB

Crane capacity

2 to 20 tonnes

Deck area

200 to 500 m2

Transferring technology

Gangway Type 1

Wave conditions

Up to 2.5 m Hs

Vessel type

CSOV

Main activities

Short term O&M contracts and commissioning contracts for windfarms or O&G projects

Accommodation

90 to 140 POB

Crane capacity

5 to 50 tonnes

Deck area

400 to 800 m2

Transferring technology

Gangway Type 1 or 2

Wave conditions

Up to 3.5 m Hs

Vessel type

ASV

Main activities

Short term commissioning contracts for windfarms or O&G projects

Accommodation

100 to 150 POB

Crane capacity

100 to 150 tonnes

Deck area

500 to 1200 m2

Transferring technology

Gangway Type 1 or 2

Wave conditions

Up to 3.5 m Hs

Name	Length	Beam	Accommodation	Deck area
SX222	89.6m	19.2m	126POB	500sqm
SX226	89.6m	19.2m	120-130POB	500sqm
SX195	93m	18m	80-120POB	500sqm
SX234	68.7m	17.0m	47POB	125sqm
SX250	47.0m	12.5m	32-40POB	65sqm

Proven CSOV/SOV designs

Operate with confidence using CSOV and SOV designs proven in real-world walk-to-work projects. Ulstein brings decades of experience from offshore wind and oil and gas. Our vessels deliver reliable performance in demanding conditions. Explore our references to see how they perform at sea.

Flexible global shipbuilding

Build where it suits your project. Ulstein supports construction at our yard in Norway or through trusted partner yards worldwide. We guide you from design to delivery, including upgrades and redesign when needed.

SX222

ZHI CHENG 60

Seaway Moxie, a Walk-To-Work Installation Support Vessel (ISV), photo by Flying Focus.

Seaway Moxie (Wind Dedication)

Name	Yard Number	Built	Owner
Windea Carnot	322	2026	Epimetheus GMBH & CO. KG
Olympic Notos	319	2024	Olympic
WINDEA La Cour	309	2016	Bernhard Schulte Offshore/ICBC Leasing
Acta Pegasus		2025	Acta Marine
Acta Centaurus	313	2019	Acta Marine B.V.
ZHI CHENG 60		2024	Shanghai Electric Windpower Group
Seaway Moxie (Wind Dedication)		2014	CBED

All CSOV/ SOV references

From the field

Mastering walk-to-work operations: The total number of walk-to-work (w2w) vessel designs and redesigns by Ulstein now counts 23, of which 21 are currently in operation. On average, these vessels perform repair and maintenance on more than 5,000 turbines every year! That makes a stunning 95,000+ gangway connections!
Read more
The captain who took delivery of all four vessels, and why an ice cream machine matters offshore: A front-row seat to the TWIN X-STERN® series: Onboard a typical CSOV, the ship's hospital is stocked with seasickness tablets and dry biscuits for technicians unaccustomed to offshore conditions. On Windea Carnot, demand for seasickness remedies is nearly zero. Instead, the three-flavour ice cream machine has become one of the most popular features.
Read more
The hidden cost driver in offshore wind: Why vessel operability matters more than ever for reducing LCOE; Vessel uptime has become a critical enabler of project performance.
Read more
Big fuel savings on first CSOV newbuilds with Ulstein’s TWIN X-STERN® concept: Taking bold commercial risks on novel vessel concepts with a strong focus on sustainability has made Olympic a pioneering player in the offshore energy sector. Its latest investment in a pair of new-build Construction Service Operation Vessels (CSOVs) based on Ulstein Group’s innovative TWIN X-STERN® solution has paid off, with close to 50% reductions in fuel consumption and emissions to boost environmental performance.
Read more

Frequently Asked Questions (FAQs)

A CSOV, or commissioning service operation vessel, is a purpose-built ship that supports the construction, commissioning and maintenance of offshore wind farms. It works as a floating base where technicians live and work through offshore campaigns lasting several weeks. Motion-compensated walk-to-work gangways, cranes and dynamic positioning let technicians transfer to turbines and keep working in higher sea states than smaller craft allow.

An SOV, or service operation vessel, is a purpose-built ship that supports the operation and maintenance of offshore wind farms once they are in production. It stays on field for long periods, housing technicians who transfer daily to turbines using a motion-compensated walk-to-work gangway. Dynamic positioning, onboard workshops and spare part storage keep maintenance work running through the seasons with less reliance on shore.

Both vessels house technicians offshore and use motion-compensated walk-to-work gangways, but they serve different phases. A CSOV supports construction and commissioning, working in campaigns that move with the project and often carrying heavier lifting capacity for component work. An SOV serves wind farms already in production, staying on field under long-term contracts to handle routine maintenance and repairs. In practice the designs overlap, and many owners specify vessels that can do both.

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.

Dynamic positioning (DP) is a computer-controlled system that automatically keeps a vessel in position using its own thrusters. Sensors such as GPS, gyrocompasses and wind sensors continuously monitor the vessel's location and movement. A control computer calculates how much thrust is needed to counteract wind, waves and current, allowing the vessel to maintain its position without anchoring.

Offshore wind operations often require vessels to work close to turbines while personnel, equipment and spare parts are transferred. Dynamic positioning allows the vessel to maintain a precise and stable position despite changing weather and sea conditions. This is essential for safe Walk-to-Work operations, as even small movements can affect the gangway connection. Reliable DP improves safety, increases operational uptime and helps maintenance work continue in a wider range of conditions.

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.

See the explanatory movie here.

Ulstein has designed or redesigned 23 walk-to-work vessels to date, of which 21 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.

Start your next project

Talk to us about your walk-to-work vessel requirements and find the right solution for your offshore fleet.

Geir Heltne

Description: Sales Manager
Affiliation: Ulstein Design & Solutions AS

[email protected] +47 975 13 704

CSOV & SOV

A track record you can check at sea

Built for demanding offshore operations

Designed for owners who need to deliver from day one

Designed for performance and efficiency

Reduce risk and improve uptime

What is the difference between crew transfer vessel (CTV), service operation vessel (SOV), commissioning service operation vessel (CSOV) and accommodation support vessel (ASV)?

Start your next project

Explore our CSOV & SOV vessel portfolio

Proven CSOV/SOV designs

From the field

Mastering walk-to-work operations

The captain who took delivery of all four vessels, and why an ice cream machine matters offshore

The hidden cost driver in offshore wind

Big fuel savings on first CSOV newbuilds with Ulstein’s TWIN X-STERN® concept

Frequently Asked Questions (FAQs)

Start your next project

Geir Heltne

Energy: Explore other vessel designs

Anchor Handling Tug Supply

Cable Lay

Diving Support

Drilling

Emergency Response Rescue

Heavy Lift

Heavy transport

Jack-up

Oceangoing Tugs

Pipe Lay

Platform supply

Seismic research

Subsea