Written by: Collin Fields, Marketing & Communications Manager, OWA
When industry professionals talk about operations and maintenance (O&M), the discussion almost always centers on fixed-bottom wind farms. That is understandable considering they represent most of the installed capacity worldwide, and the industry has spent nearly two decades refining how to keep them running. But as floating offshore wind (FOW) progresses from pilot projects toward commercial-scale deployment, the playbook that works at a monopile site becomes increasingly inadequate.
Floating offshore wind is widely regarded as a critical enabler of the global energy transition. By allowing turbine deployment in deeper waters where wind resources are stronger and more consistent, this technology unlocks substantial clean energy potential. However, the distinct operational and maintenance (O&M) challenges associated with floating systems demand tailored strategies to ensure reliable performance and long-term asset integrity.
Floating offshore wind is not simply a turbine installed with a new foundation in deeper water. It is a fundamentally different technology, and it requires a fundamentally different approach to operations and maintenance. This article examines what that means in practice.
The Fixed-Bottom Baseline
To understand what changes for floating wind, it helps to understand how O&M currently functions for fixed-bottom projects.
At a typical fixed-bottom site, routine maintenance is performed using crew transfer vessels (CTVs) that shuttle technicians from a nearby port to the turbines. For larger corrective jobs, service operation vessels (SOVs) are deployed, often capable of housing crew for extended offshore campaigns. For major component replacements, such as a gearbox or generator, the industry relies on jack-up vessels (JUVs) or heavy-lift vessels (HLVs) that can position a crane directly over the turbine tower.
Image: Shanghai Zhenhua Heavy Industries Co., Ltd
This system works because fixed-bottom turbines sit in relatively shallow water, typically less than 60 meters, with a stable foundation anchored to the seabed. The vessels that support them are well understood, available in quantity, and matched to the operational environment. O&M already accounts for up to 30% of the overall cost of energy for fixed-bottom projects [McMorland et al., 2022], which has driven continuous improvement in logistics, vessel design, and predictive maintenance tools. By most measures, the industry has gotten quite good at this.
The moment the foundation starts floating, most of those assumptions have to be revisited.
What Changes When the Foundation Floats
Floating wind turbines introduce components that simply do not exist on fixed-bottom projects: mooring lines, anchor systems, dynamic inter-array cables, and the floating substructure itself. Each of these carries its own inspection requirements, failure modes, and maintenance demands.
Beyond the new hardware, the operating environment changes significantly. FOW projects are typically sited in deeper water farther from shore, which means harsher sea states, longer transit times for maintenance vessels, and narrower operational weather windows. Metocean conditions that might restrict a few days of access per month at a nearshore fixed-bottom site can restrict weeks of access at a far-offshore floating site. That lost time translates directly into lost revenue and compounding logistical costs.
Then there is the issue of motion. Despite being anchored with mooring lines, floating turbines still move around. Even in moderate sea conditions, the platform pitches, rolls, and heaves, and those motions are amplified as they travel up the tower to the nacelle. For technicians working at height, this creates safety risks and physical strain that have no equivalent on a fixed-bottom project. Research has found that adherence to human exposure guidelines for motion and acceleration can reduce available weather windows for maintenance activities by up to 5%, a figure that carries significant financial consequences when applied across an entire project lifetime.
Crew access itself becomes more complex. On a fixed-bottom turbine, a technician steps from a vessel onto a static structure. On a floating turbine, the transfer is between two structures that are both moving. This floating-to-floating dynamic requires different vessels, different operational procedures, and different thinking about what constitutes safe access conditions.
The Jack-Up Dead End: Rethinking Major Component Replacement
One of the clearest practical differences between fixed-bottom and floating O&M involves major component replacement. When a gearbox, generator, or blade needs to be replaced on a fixed-bottom turbine, the standard approach is to mobilize a JUV or HLV. These vessels are effective, but they are limited to water depths of around 60 meters. Commercial-scale floating wind sites are designed specifically for depths beyond that threshold. At those depths, conventional heavy-lift vessels are simply not viable.
This creates a genuine engineering and logistics challenge with no single established solution.
One approach that has attracted significant research attention is the tow-to-shore (T2S) strategy. Because most floating platforms can be disconnected from their moorings and towed using tugboats, it is theoretically possible to bring a turbine to a port for major maintenance work, then return it to the site after repairs are complete. The concept eliminates the need for expensive heavy-lift vessels offshore and allows repairs to take place in controlled, sheltered conditions.
Image source: Image: Provence Grand Large, EDF
One study found that O&M costs for floating scenarios with T2S were 17 to 21 percent higher than for equivalent fixed-bottom projects, depending on whether the towing operation required a continuous weather window or could be broken into segments. Another study, analyzing sites at different distances from shore, found that T2S increased costs by between 8 and 23 percent compared to on-site maintenance, with the penalty growing as distance increased [McMorland et al., 2022]. These are not trivial differences, but they have to be weighed against the absence of viable alternatives for large component work.
The T2S strategy also depends heavily on port infrastructure. The receiving port must have sufficient water depth, handling equipment, and physical capacity to accommodate a floating turbine. Given the scale of modern turbines and their substructures, this is not a given at most existing European ports. There is also a variant approach sometimes called “tow to shallow,” in which the turbine is moved to shallower water where JUVs or HLVs can operate, without requiring a full journey to port.
Image: WindFloat Atlantic, Principle Power & Ocean Winds
Other approaches under development include floating cranes positioned adjacent to the turbine at sea, and self-hoisting equipment that would allow component replacement without external crane vessels. None of these have been deployed or tested at a commercial scale yet.
Maintenance Strategies: The Shift from Corrective to On-Site vs. Onshore
The classification of maintenance activities has shifted considerably as the industry has considered what FOW operations will actually look like in practice.
For fixed-bottom wind, the standard framework separates preventive maintenance (planned inspections and servicing) from corrective maintenance (responding to failures). Floating wind does not eliminate this distinction, but it adds a layer: whether a given task will be performed on site at the turbine’s location or onshore after towing the platform to port. That onsite-versus-onshore question is now the more operationally significant division.
Condition-based monitoring (CBM) is expected to play a larger role in floating wind O&M than it currently does in fixed-bottom operations. By continuously tracking sensor data on turbine components, mooring loads, and platform motions, operators can identify developing faults before they become failures, allowing maintenance to be scheduled during favorable weather windows rather than on an emergency basis. Given the access challenges at floating wind sites, avoiding unplanned emergency callouts is not a minor operational preference; it is a significant cost and safety consideration.
The sub-sea elements of a floating wind farm, including mooring lines, dynamic cables, and anchor systems, require periodic inspection via remotely operated vehicles (ROVs), since diver access at depth is impractical for routine work. The frequency and scope of these inspections depend on the mooring system design and the environmental conditions at the site.
Image: Fugro’s Blue Essence ROV
Vessels and Access Windows
The vessel fleet for floating wind O&M looks similar to that used for fixed-bottom projects in some respects, but with important differences.
CTVs and SOVs remain the primary personnel access tools. SOVs are particularly relevant for far-offshore floating sites, since their ability to station-keep and house crew for extended periods reduces the transit burden that would otherwise make operations impractical. Walk-to-work (W2W) vessels, equipped with motion-compensated gangways (MCGs), extend the range of sea conditions under which crew transfers can safely take place. Standard CTVs can typically transfer crew in significant wave heights up to around 1.5 meters, while W2W vessels with MCGs can operate in conditions up to 3.5 meters significant wave height, meaningfully widening the operational weather window [Ramachandran et al., 2021].
The key addition to the floating wind vessel roster is the towing vessel, specifically tugboats and anchor handling tug supply vessels (AHTSs) for T2S operations. JUVs, the workhorses of fixed-bottom major maintenance, are largely excluded from the floating wind vessel fleet at operating depths.
Condition Monitoring, Robotics, and Digital Tools
The monitoring and inspection technology applicable to floating wind O&M draws heavily on tools developed in the offshore oil and gas sector. ROVs for subsea inspection, AUVs for autonomous underwater survey, and drones for above-water visual inspection of blades and structure all reduce the need for direct human access in hazardous conditions. Projects like Hywind Scotland have already demonstrated AUV-based inspections of underwater components as a replacement for diving operations, improving both safety and inspection frequency.
Digital twins are also attracting considerable interest as a planning and optimization tool. By building a virtual model of a floating turbine and its environment, operators can simulate how different sea states and load conditions affect component wear, predict maintenance needs in advance, and optimize scheduling. The Kincardine project off the coast of Aberdeen has developed a digital twin framework specifically aimed at understanding how environmental forces interact with the turbine system, with the goal of reducing operational disruptions and extending component life.
Image: Kincardine, Floatation Energy (courtesy of Cobra Group)
Condition monitoring systems (CMS) for floating wind must track not only the drivetrain and electrical components monitored on fixed-bottom turbines, but also the additional parameters specific to floating platforms: mooring line tensions, platform motions, wave-induced fatigue loads, and the behavior of dynamic cables. This broader monitoring requirement reflects the greater complexity of this technology.
Cost Realities and the Gaps in What We Know
O&M is consistently identified as one of the largest cost drivers for floating wind projects. Depending on the methodology and assumptions used, the exploitation phase, which encompasses O&M activity throughout the project lifetime, accounts for between 25 and 30 percent of total lifecycle costs across the main floating structure types [McMorland et al., 2022].
What makes cost modeling for floating wind difficult is the limited availability of real operational data. With only a handful of projects at pilot or demonstration scale, the industry lacks the failure rate databases, maintenance time records, and vessel utilization data that underpin fixed-bottom O&M planning. Researchers have largely worked around this by adapting fixed-bottom data and applying statistical techniques, but the uncertainty in those estimates is substantial.
The choice of floating structure type, whether spar, semi-submersible, or tension leg platform (TLP), also affects O&M strategy and costs in ways that are still being determined. Semi-submersible platforms are generally considered the most straightforward for O&M purposes, since they can be towed back to port without heavy-lift vessels and have relatively accessible mooring disconnection procedures. Spar platforms, by contrast, require deep water ports and may need heavy-lift vessel assistance for major repairs. TLPs offer certain structural advantages but involve complex mooring disconnection procedures that complicate both onshore maintenance and decommissioning.
Case Studies: What Hywind Scotland and Kincardine Have Taught Us
The world’s first commercial floating wind farm, Hywind Scotland, has provided the most sustained operational dataset available for floating wind O&M. Commissioned in 2017 with five 6 MW spar-type turbines 30 kilometers off the Aberdeenshire coast, the project has demonstrated that floating wind can achieve strong availability and production performance, boasting a capacity factor of around 57% [McMorland et al., 2022]. The O&M approach at Hywind Scotland includes campaign-based inspections, ROV-based subsea monitoring, and heavy component exchange using offshore service vessels for components up to a certain weight threshold. For larger components, turbines would need to be towed to a sheltered location for heavy-lift vessel assistance.
Image: Hywind Scotland, Equinor
Kincardine, a 50 MW semi-submersible project off Aberdeen, is the largest floating wind farm currently in operation. Its O&M approach has incorporated digital twin technology to model the interaction between environmental loads and turbine behavior, enabling more informed maintenance planning. The semi-submersible configuration at Kincardine also illustrates one of the practical advantages of that platform type: the ability to tow the structure to port for major repairs without specialized heavy-lift vessels, using local tugs instead.
Image: Kincardine, Flotation Energy
Both projects are also a reminder of what happens when an industry learns by doing. The operational experience accumulated at these sites, however limited in scale compared to what commercial deployment will require, is forming the foundation of the knowledge base that future projects will depend on.
Looking Ahead
The floating offshore wind industry is at an inflection point. The ScotWind leasing results alone awarded 15 GW of floating wind capacity across 11 projects, with most sites located more than 100 kilometers from the nearest shoreline. Executing O&M across that kind of portfolio will require purpose-built port infrastructure, a new generation of vessels suited to floating-to-floating transfer, standardized procedures for T2S operations, and a much richer dataset on component failure rates and repair times specific to floating platforms.
The transfer of knowledge from offshore oil and gas is valuable, but it is not a complete solution. Floating wind turbines are unmanned assets, produced in large numbers, designed to operate in dynamic environments, and expected to remain on-site for 20 to 25 years with minimal intervention. That combination of characteristics does not have a direct precedent, and the O&M strategies developed to support it will need to be built with that reality in mind.
References
McMorland, J., Collu, M., McMillan, D., & Carroll, J. (2022). Operation and maintenance for floating wind turbines: A review. Renewable and Sustainable Energy Reviews, 163, 112499. https://doi.org/10.1016/j.rser.2022.112499
Ramachandran, R.C., Desmond, C., Judge, F., Serraris, J.J., & Murphy, J. (2021). Floating offshore wind turbines: Installation, operation, maintenance and decommissioning challenges and opportunities. Wind Energy Science (preprint). https://doi.org/10.5194/wes-2021-120
McLean, S. (2024, October 25). Lessons learned from heavy maintenance at the world’s first commercial floating wind farm. Spinergie. https://www.spinergie.com/blog/lessons-learned-from-heavy-maintenance-at-the-worlds-first-commercial-floating-wind-farm
Copyright: Offshore Wind Academy