Floating offshore wind (FOW) offers a huge opportunity to tap deeper waters and often stronger and more consistent wind resources in them.

But it’s still early days for the sector, with significant technical and economic challenges to overcome in order to scale up. With the help of Will Brindley, Lead Naval Architect at Apollo Engineering, I’ve been exploring some of these challenges.

A key element in de-risking offshore wind in dynamic deepwater environments is the smart application of condition monitoring systems (CMS) and advanced data processing.

The current status: ramp-up and learning

The consensus across the industry is that FOW is currently ramping up, but the detailed engineering needed for gigawatt-scale projects (we’re talking 50 to 100 turbines) is just beginning.

This is why many are taking a phased approach—moving from smaller projects (like the 300 MW initial capacity for Equinor’s Celtic Sea project) to much larger 1.5 GW arrays—to test technologies and refine designs.

To an extent, we’re already seeing that. The industry has several small demonstrator projects in the water, providing essential early lessons. One of those is the need to focus as much on what went wrong as what went well.

A good example is the Kincardine project, near Aberdeen. This showed that while major component replacement is expensive (involving towing the unit to Rotterdam and back), successfully executing an in-field replacement was a big win in terms of sector learnings.

With intense pressure to reduce costs in this sector, the demonstrators are vital for these types of learning and we can also learn more from elsewhere.

Industry learnings

Floating structures have been used for decades. The oil and gas industry has 30-40 years’ experience in this area, particularly concerning floating production units (FPSOs), mooring integrity and cable data. There’s a vast amount of information on mooring failures, monitoring techniques and how to protect subsea systems.

This legacy can help FOW developers create a robust through-life strategy, including comprehensive monitoring and repair strategies. But, of course, there’s a caveat. The unique operating profile of a floating wind turbine creates different design drivers compared to traditional oil and gas assets.

What are the main challenges in floating offshore wind?

Fatigue and structural integrity

Unlike an FPSO, where maximum loading might occur once a year during a 100-year storm, a floating turbine attracts near-maximum loading half the time it is operating (at typical rated wind speeds of around 12 m/s). This extreme and frequent loading means that FOW structures and their mooring systems are overwhelmingly governed by fatigue requirements.

Fatigue is a cyclic issue where tension and bending cycles accumulate over time, creating a crack that ultimately leads to failure. Fatigue is complex because it interacts critically with other failure modes:

• Corrosion: Cracks propagate much faster in a heavy corrosion environment.

• Microbial corrosion: Over 10-20 years, microbial corrosion can cause localized pitting, acting as a stress raiser that accelerates fatigue cracks.

• Wear: Things moving and wearing against each other are difficult to calculate and model accurately.

If left unchecked, a single small crack can lead to a major collapse.

Mooring system failure

In terms of mooring failure, this is a catastrophic risk to both floating offshore wind farms and FPSOs – it’s just that the catastrophe happens in different ways.

Historical FPSO mooring failure incidents (like the Gryphon Alpha and Banff FPSOs in 2011) showed that a failure caused by a storm can lead to around half a billion pounds of damage, primarily from repair costs due to the drifting structure destroying subsea infrastructure. For floating wind, a dragging chain acts effectively like a wrecking ball through a wind farm, potentially causing multiple subsequent failures.

Based on oil and gas statistics, it’s possible to expect 1-2% of mooring lines per asset to fail per year. At a large array scale (for example 50 turbines), this translates to approximately one mooring failure per year.

To address these risks, developers are increasingly turning toward synthetic ropes for their mooring designs. Rope cuts out the three main failure modes seen in steel chain moorings: fatigue, corrosion and wear.

However, ropes introduce a new weakness: they are sensitive to being cut by external factors like fishing trawlers, errant anchors or even sabotage. Managing this vulnerability is crucial. Studies have showed that even small tweaks in mooring design can cut the overall risk by a factor of 10. More details on this are expected in an upcoming ORE Catapult study on repair and integrity management strategies being authored by Apollo.

How does smart condition monitoring apply to floating offshore wind?

Given the criticality of fatigue and the costs associated with a catastrophic failure, developers should look to implement condition monitoring systems (CMS) in their projects. A smart CMS can enable advanced condition monitoring, predictive maintenance and real-time data analysis, ensuring long-term reliability and reduced operational risks.

This isn’t just about monitoring asset behaviour, but also proactively informing predictive maintenance and triggering inspection campaigns.

Three steps to a smart condition monitoring

• The foundation: Baseline measurements monitoring must begin early. Manufacturing quality and oversight are crucial as production scales up dramatically (from tens of kilometres of chain to thousands, for example). To ensure subsequent inspection data is meaningful, it is important to conduct a robust “as-built” baseline survey once the system is installed. Without knowing the starting point (for example, the exact size and condition of each chain, as installed), data collected five or 10 years later is almost useless to measure its expected life time.
• The cloned array strategy: A key opportunity unique to FOW is the vast scale of the arrays, typically consisting of 50 to 100 near-identical, or “cloned”, assets. This cloning allows operators to implement a sampling strategy. By fully monitoring a small sample of mooring lines, structure bits or cables, operators can infer what is happening to the rest of the field, potentially using a 5-to-1 or 10-to-1 benefit from each monitoring device. This means that engineering efforts and monitoring costs for a single unit can be applied across the entire array, creating a strong business case for upfront investment.
• Implementing robust sensing: To effectively monitor these assets, particularly for mission-critical functions like excursion monitoring and turbine behaviour, the hard sensor technology must be incredibly reliable.

Decades of dynamic expertise

At Sonardyne, we bring decades of experience in positioning and monitoring underwater infrastructure, having been active in this field since 1971. Over the years, we have developed expertise in monitoring dynamic subsea cables and structures in challenging offshore environments, supporting oil and gas platforms, deepwater installations and marine renewable energy projects.

This heritage means our solutions for floating offshore wind condition monitoring and fatigue analysis build on years of trusted technology proven in complex subsea applications.

Dynamic subsea cable monitoring

For floating offshore wind, we use acoustic sensors to measure the 3D shape, position and environmental influences on dynamic subsea cables in real time. This is data our instruments can then wirelessly transmit through the water to the structure or a service vessel, providing real-time and/or on-demand information about the structure.

Our sensors can also be used to support other, third-party monitoring, such as load cells, during structure installation, transmitting information from a mooring line during tensioning, for example.

Wave and current monitoring

As well as monitoring assets, we provide the ability to understand the environment they are in – and forces they must withstand – with our Origin 600 acoustic Doppler current profiler (ADCP). With onboard data processing and an integrated acoustic modem for through-water wireless communication, it provides wave and current information that can be accessed at any time, on-demand. This is critical for understanding cable behaviour and fatigue risks.

In today’s uncertain world, we also provide highly reliable, redundant positioning solutions to counter modern threats like jamming and spoofing of GPS/GNSS networks. Operators can patch up signal dropouts by combining high-accuracy GPS with our compact, hybrid inertial-acoustic system, SPRINT-Nav, ensuring a continuous, guaranteed quality position accuracy for the whole array.

A strategic approach to monitoring

Our suggested general strategy for sensor placement is to maximize dry sensing housed in the turbine structure. Subsea sensors, which have a limited lifespan and significant overhead for installation and maintenance, should be used sparingly—perhaps on 10–20% of the assets—to cross-validate models and fill in data gaps.

They don’t have to be everywhere but crucially, real-world sensors are the only way to validate complex models. Hard sensing, such as shape sensing on dynamic cables, allows developers to see real-world effects, like tidal influences on the cable touchdown point, providing the necessary confidence to refine models and coefficients.

What is the future for floating wind operations?

As the sector matures, the industry will have to tackle what will be a growing challenge of data handling. The techniques we have today, such as laser scanning and photogrammetry, acquire massive amounts of data (terabytes), creating a processing bottleneck.

Here, artificial intelligence (AI) can be a critical solution. While the application of AI in monitoring data is still being explored, it is an extremely good fit for processing large amounts of inspection footage and datasets. By classifying and validating data automatically, AI can enable continuous, year-on-year analysis at scale. However, human oversight and validation remain critical to maintain trust in the processing.

Smart CMS and AI data could enable a shift away from routine, scheduled inspections (like 100% visual inspection) to focused, predictive inspection campaigns. CMS won’t replace inspection, but it can focus time and resources on failure modes that the monitoring system identifies or cannot detect.

What role do advanced robotics and autonomy play in floating offshore wind?

As we move forward, the industry can also evolve beyond the current inefficiency of deploying 70 m surface vessels with 50 people just to pilot an ROV. Future operations and maintenance strategies can incorporate advanced robotics and autonomy.

This could involve autonomous inspection systems (resident vehicles or autonomous surface vessels controlled from shore) that can perform routine inspections at a tenth of the current cost.

An ideal future system could be complementary: monitoring systems supporting underwater inspection, which is in turn supported by an autonomous inspection fleet.

Finally, for the sector to achieve bankability, standardisation is needed. Currently, there is a lack of consensus on condition monitoring requirements, redundancy levels and alarm thresholds. While every wind farm is different, a general consensus on required monitoring levels and the value extracted from data is necessary to build confidence across finance, insurance and design sectors.

Confidence—whether the news is good or bad—allows problems to be addressed early, generating value and sustaining long-term asset performance.

Read more

Understanding waves and currents is crucial for FOW safety and cost efficiency. Real-time data from our Origin 600 ADCP optimizes operations, minimizing stress, cable scour and crew transfer risks from significant waves. Learn more in our case study.

Read how sea trials showed how we worked with partners to use our acoustic positioning and ADCP data to track dynamic cable shape and environmental forces, revealing tidal-driven seabed contact.