In offshore wind, Service Operation Vessels (SOVs) often serve as an offshore base for accommodating and transferring technicians, tools and parts to and from wind turbines or substations. By maximizing working time offshore, they are taking on an increasingly critical role in the efficient running of operations and maintenance (O&M) phases. In recent years, the SOV market has been rapidly expanding.
Within the wider SOV umbrella is the Construction Service Operation Vessel (CSOV) fleet which is attracting increasing attention. CSOV is a common designation for SOVs operating during the construction or commissioning phase of the wind farm; they are generally larger vessels, with greater length, accommodation, and deck storage capacity. The analysis here identifies CSOV as SOV operating during the construction phase of the wind farm.
Here, we examine the market impact of the growing SOV sector alongside the burgeoning CSOV fleet.
The SOV market approaches full utilization
The SOV market is one of the most active in the offshore industry, with utilization rates frequently exceeding 90%. Growth is driven by long-term contracts, sometimes lasting up to 15 years, between vessel owners and wind developers or turbine manufacturers. These agreements provide stability for both operators and service providers.
While primarily serving offshore wind operations, SOVs can also support oil and gas projects when necessary. Their deployment depends on factors such as distance to shore, weather conditions, and operational requirements. In certain O&M scenarios, such as harsher weather conditions or for when wind farms are further from the marshalling port, SOVs are preferred over Crew Transfer Vessels (CTVs).
Half of the SOV fleet is currently under construction
The SOV market is expanding rapidly with 70 new units, including 19 under option, expected in the coming years. Notably, 20% have already secured a contract with an operator or a turbine manufacturer prior to delivery. Furthermore, over 50% of vessels on the order books are designed to have alternative fuel capabilities. This includes 25 units that are aimed to operate on methanol fuel to align with industry decarbonization efforts.
Edda Wind is set to be the SOV market leader with 10 CSOVs and three SOVs. They also have four optional CSOVs. Their C/SOV fleet is divided between two designs:
- VARD 4 25: 87.5m length, 19.5m beam with 320 m2 deck area and 120 accommodations.
- Salt Ship 0217: 88.3m length, 19.7m beam, 500m2 deck area and 120 accommodations.
Read More: Decarbonizing the offshore vessel fleet: the three key methods to reach net zero
The role of CSOVs across the construction lifecycle
CSOVs play multiple, vital roles during a wind farm construction project:
- IAG Termination & Testing – CSOVs provide support operations by securing cable terminations inside the tower during array cable pull-in at a turbine. They also perform insulation resistance, continuity, and high voltage tests to ensure proper connections.
- Foundation Completion Work – CSOVs facilitate the installation and securing of secondary structures, such as boat landings, ladders, and platforms to prepare the foundation for turbine installation. This phase includes final inspections, bolting, welding, and protective coating applications.
- Wind Turbine Commissioning – CSOVs support the testing and verification of all mechanical, electrical, and control systems to ensure turbines operate as designed. This includes functional checks, system calibrations, and initial energization.
During each phase, light crane operations are required during each phase. These operations entail handling equipment and transport tools and bringing test devices and spare parts to the turbine location. These tasks have been traditionally handled by medium multipurpose and construction vessels. However, Spinergie analysis indicates that CSOVs are taking a greater market share as they begin to replace these other assets.
The chart above provides a better understanding of when the fleets come into play. The operation time has been normalized compared to the full construction period. The operational day is scaled between the construction start and construction end. The ‘full commissioning date’ comes after the end of the construction period.
Why CSOVs are gradually replacing the traditional support fleet
Historically, offshore wind construction has depended on construction and multipurpose medium vessels with crane capacities of 50 to 500 tons. However, these vessels were originally designed for use in the oil and gas industry. This has led to supply constraints when O&G demand is also high. These vessels also display inefficiencies for certain offshore wind tasks due to their large crane and heavy equipment onboard.
This has left the market receptive to CSOVs and their use has been increasing since 2022. This market shift has reduced competition with oil and gas, improved vessel availability, and optimized vessel design for operations on offshore wind projects.
Some of the key advantages CSOVs hold over traditional crane vessels are:
- Purpose-built for the task,
- Smaller crane vessel compared to O&G assets,
- Improved onboard standards (accommodation, storage, etc.),
- Lower risks and operational costs (term contracts, no competition with other industries), Optimized fuel efficiency
Spinergie’s demand estimation model
Spinergie’s offshore wind farm forecast incorporates detailed metrics, including distance to shore and project scale, to estimate the number of new CSOVs required to support the ambitions of the offshore wind sector.
The growth in the CSOV market remains very regional. Northern Europe is seeing rapid expansion, driven by recent vessel deliveries and major industry players.
Several newly delivered vessels in late 2024 have now entered operation:
- Edda Wind’s Vestri Enabler has started operations at EDF’s Neart na Gaoithe.
- North Star Group’s Grampian Tweed and IWS’s IWS Seawalker are now deployed at Dogger Bank’s offshore wind farms.
For now few SOVs are being utilized to support construction and commissioning work in other regions. Spinergie analysis indicates that at least four newbuilds will operate in APAC, mainly to support the Taiwanese market.
Spinergie anticipates that 60 SOV or CSOV units will be delivered by the end of 2026 to support growth across all wind farm lifecycle phases. Demand for CSOVs remains particularly strong in the construction and commissioning market.
By 2030, Spinergie forecasts a demand of 64 full-time vessels dedicated solely to construction and commissioning, representing a potential 230% increase compared to 2024. Spinergie’s Offshore Wind Installation Forecast predicts that 37% of demand will remain unsatisfied between 2029 and 2031, representing 23 full-time CSOVs at risk.
We have created a comprehensive study providing a detailed analysis of SOV/CSOV and CTV demand in the offshore wind sector through 2040. Find out more about what the study contains, and how to access it here.
(Feature image: CSOV Purus Chinook was delivered in April 2025. It is under long-term charter with Vestas supporting offshore wind operations. Picture via Alamy)
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