Author: Chris Nelson, PhD, Senior Data Scientist
The offshore renewable energy industry is expanding at a rapid rate. The poster child of this progress is offshore wind, with massive farms of turbines being operated and built throughout the world. These wind farms now supply significant amounts of clean energy to the grid, with estimates suggesting up to 17 % of the UK’s supply came from this source in 2023. Below the waves, though, sits another massive, yet currently under-utilised energy source. Unlike wind, which relies on the occurrence of specific weather conditions, this other offshore renewable energy source is entirely predictable making it the perfect method to balance the ever-changing demands of an electrical grid. This energy source, of course, comes from the tides.
Although both, on the face of it, operate in similar environmental conditions, the risks faced by cables supplying energy from offshore wind farms and tidal arrays are often quite different. Wind farm export and inter-array cables are typically well buried in the seabed sediment, protecting them from the movement of the tides and from potential anchor strikes. This means (there is at least a perception) that the cables themselves are relatively stable and do not move considerably. As such, the main question we are asked by windfarm operators is ‘Are my cables still nicely buried and, therefore, protected?’ (Read more about Cable Burial). Tidal arrays are different. By definition, tidal arrays operate in some of the strongest tidal flows in the world, with these flows washing away large amounts of the sediment leading to a harsh, rocky seabed. The cables that link the tidal arrays to shore must, then, lie on top of this bedrock exposed to the harsh conditions. Given this, the main question we are asked by tidal operators is ‘Which parts of my cables are moving the most in the tide?’
Here at Indeximate, we use the rich and versatile data provided by Distributed Acoustic Sensing, or DAS, to help offshore renewable energy providers, regardless of whether they look above or below the waves, answer these questions. In this blog post, we discuss how our two years’ of continuous monitoring at the MeyGen tidal array – often referred to as the largest tidal array project in the world – has helped them better understand the risks faced by their cables in the harsh environmental conditions of the Pentland Firth. Specifically, we discuss how our methods have helped to identify persistent risk areas along the cables, inform where preventative action could be taken, and then confirm whether the action was successful.
Which parts of my cables are moving the most in the tide?
Answering this question requires a deep physical understanding of how different types of movement along a cable present in DAS data. Abrasion (the cable moving smoothly over the rocky seabed) has a different signature to cable skipping (where the cable is getting caught on rocky outcrops as it moves) which in turn has a different signature to tidally induced vibrations (the cable oscillating due to water flowing around it). Of course, cables are designed to withstand some of these effects, but in extreme tidal flows, they can be pushed to their limits leading to a gradual reduction in their effective lifetime.
The gradual nature of the risk posed by these phenomena creates a challenge for DAS operators. DAS has typically been used for event detection, essentially using the huge amounts of data returned by this method to understand what is happening in the here and now before quickly deleting the data to make room for more. To identify long-term trends such as those caused by the tides though, a long baseline of measurements are required which means a different approach is needed. This is why we at Indeximate compress the
raw DAS data, before uploading it to the cloud where it can be stored and analysed in detail. This is what we have been doing at MeyGen for around 2 years, providing us with a vast amount of data (petabyte scales) which can be used to identify persistent risk areas.
From Identification to mitigation
Identifying persistent risk areas with the confidence necessary to justify action requires time. The strengths of risks felt by the cable (such as the number of abrasion events that occur in a day) changes with the strength of the tide, which varies on daily, monthly, and seasonal cycles. In Figure 1, we plot the tidal vibration (top) and abrasion (bottom) risks felt at different positions along a cable over the course of around one month. Neither graph is constant indicating that the amount of risk felt by the cable varies along its length. Importantly, some locations feel both tidal vibration risk and abrasion risk, some just feel one, whilst most of the cable is nice and calm. Through our long-term monitoring and Scattersphere interface, we were able to identify the specific locations in the MeyGen cable eco-system that were experiencing the most combined risk through time, allowing us to identify a short-list of locations where mitigation measures would be most effective in stabilising the system.
After identifying these locations and discussing with the MeyGen team about the types of risk that were present, it was agreed that preventative maintenance was required and that a rock placement campaign would be the best approach. As such, the O&M team at MeyGen liaised with their industrial partners to organise the campaign, which placed 12 4-tonne rock bags at the end of summer 2025. Two photos from this campaign are included in the top row of Figure 2, whilst a third from a follow-up survey in the spring of 2026 is included in the bottom row of Figure 2 (courtesy of Fraser Johnson, O&M Manager, MeyGen). To support this campaign, Indeximate went back to the roots of DAS to perform real-time event detection, confirming that the rock bags were placed in the correct location.
The beauty of continuous monitoring is that the effects of the mitigation efforts can easily be seen over the following weeks and months. At many of the targeted locations, the drop in the risk related movement experienced by the cable was startling, with measured values dropping by an order of magnitude. Indeed, the position along the cable ecosystem that was previously highlighted as the location experiencing most risk was stabilised to an extent that it was no longer returned as a risk location through our analysis. In Figure 3, we plot an example of this, using the tidal vibration risk at one of the locations at which rocks were placed. The time of the rock placement is indicated by the vertical dashed line, with the risks before being clearly much higher than the risks after. The cable is clearly now experiencing less movement related to the tidal flows, indicating that it is better protected against the viscous tides of the Pentland Firth.
As the offshore renewables industry expands over the coming years, preventative maintenance such as this is going to play an ever-growing role. The wait-to-fail approach not only leads to avoidable downtime, but it also leads to bottlenecks in the system, piling pressure on over-stretched O&M teams during peak periods.
Fraser Johnson, O&M Manager at MeyGen, explains the strategic importance of this shift: “MeyGen’s approach to subsea cable integrity sits within a broader asset management strategy shaped by years of operating tidal energy systems in one of the world’s most challenging high-flow marine environments. As insurance rates and deductibles have continued to rise, MeyGen has moved away from the traditional ‘insure-and-forget’ model and adopted a proactive, risk-based approach focused on prevention, early detection, and targeted intervention. This strategy relies on continuous monitoring, data-driven assessment, and timely mitigation to safeguard the export and array cables—critical assets that underpin the long-term reliability and commercial resilience of the MeyGen tidal array.”
The success of this approach at MeyGen clearly indicates how DAS and Indeximate can play a key role in facilitating these efforts. We look forward to continuing our work with MeyGen over the coming months and years helping to secure their cables, making this world-leading tidal array an even bigger success story.
If you want to learn more about how we can identify risks along your cables, feel free to reach out by contacting us below.
