The Cost Question Nobody Asks
When an offshore wind operator budgets an inspection campaign, the headline number is the vessel and ROV mobilisation cost. A North Sea inspection vessel with an ROV system runs at a day rate between £15,000 and £35,000 depending on vessel class and specification. A 10-day campaign covering 25 foundations costs between £150,000 and £350,000 for the survey operation alone. That is the number that gets challenged in planning meetings. It gets compared to alternatives, optimised for weather windows, and scrutinised for scope.
The documentation phase does not receive the same scrutiny, partly because it does not arrive as a single invoice and partly because it is absorbed across internal engineering time and inspection contractor day rates that are already part of ongoing operational budgets. But when you add up the engineering hours and apply realistic day rates, the documentation cost for a typical 25-foundation campaign often exceeds the vessel cost.
This article is an attempt to make that cost concrete, drawing on the operator discussions that informed our early-access programme. We are not presenting audited financial data. We are working from detailed conversations with inspection engineers and asset managers about how they spend their time and what that time costs. The figures are realistic for mid-size UK offshore wind operators, not an upper or lower bound.
Breaking Down the Documentation Engineering Hours
Consider a typical 25-foundation monopile inspection campaign generating 200 hours of ROV footage. The documentation phase has four main components:
Video review: A qualified inspection engineer reviews the footage and produces an anomaly log. At a realistic review pace of 1x to 2x speed for sections requiring attention, covering 200 hours of footage takes 60 to 100 hours of active review time. Allow for a review engineer at a contracted day rate of £800 to £1,200 per day working on this as a primary assignment: the review step alone costs £7,000 to £15,000 in direct engineering time.
Report assembly: A senior engineer converts the anomaly log into a structured compliance document. For 25 foundations with a mixed findings profile, this is 15 to 25 hours of work. At a senior engineer day rate of £1,200 to £1,500, that is £2,500 to £5,000. Add in the internal quality review step, which for a compliant programme requires a second engineer to check the report before submission: another 8 to 12 hours at comparable rates.
Rework cycles: Reports rarely go from first draft to accepted submission without revision. A single revision cycle, responding to client clarifications on specific findings, adds 8 to 15 hours of engineer time across the report writer, the reviewer, and any footage retrieval required to answer specific questions. Two revision cycles, which is common for programmes with significant findings, doubles that.
Client-side review: The operator's asset integrity team reviews the delivered report and provides acceptance or feedback. For larger operators, this involves a senior engineer spending 4 to 8 hours reviewing a full campaign report. This cost is internal to the operator rather than charged to the inspection contractor, but it is a real engineering cost. At an internal senior engineer cost of £900 to £1,400 per day, that is £500 to £1,400 per campaign report.
Totalling the Documentation Cost
Summing these components for the 25-foundation example: video review at the lower-middle of the range (£10,000), report assembly including internal QA (£6,000), a single rework cycle (£2,500), client-side review (£1,000): total documentation cost of approximately £19,500 for the documentation phase of a campaign that cost £200,000 to £250,000 for the survey itself.
That ratio, roughly 8 to 10 percent documentation cost against survey cost, might sound acceptable. But the picture changes when the rework cycle extends to two or three iterations, which adds another £5,000 to £10,000. And when the programme has a challenging findings profile requiring additional footage retrieval and specialist input, those costs can double again. The documentation phase for a complex programme can reach £40,000 to £60,000. A survey campaign that cost £200,000 for the vessel now has a documentation cost of 20 to 30 percent on top.
The more significant comparison is not documentation-to-survey cost, but documentation cost per asset. At £19,500 across 25 foundations, that is £780 per foundation for the documentation phase. Over a wind farm's 25-year design life with biennial or triennial inspection cycles, a 100-turbine array generates 800 to 1,200 foundation-inspection-documentation events. At £780 per event, the cumulative documentation cost is £624,000 to £936,000, at today's rates. That is engineering budget that produces compliance records, not maintenance interventions or operational improvements.
What the Hours Are Actually Spent On
The frustration expressed by every inspection engineer we spoke to is not that the documentation work is unnecessary. It is that a substantial portion of the engineering hours are spent on tasks that are not using their expertise. Watching footage at 1x speed to locate and log anomalies they already reviewed at survey planning stage is not where a £1,200 per day engineer adds value. Reformatting a spreadsheet anomaly log into a report template is not why they developed 10 years of offshore inspection expertise.
The expensive part of an inspection engineer is their judgment: their ability to assess whether a condition rating is appropriate, whether a trend across surveys indicates a maintenance intervention is warranted, whether an anomaly cluster suggests a systemic issue with the corrosion protection system. That judgment is a small fraction of the documentation hours in a typical manual workflow. Most of the hours are mechanical: watching, logging, reformatting, checking.
This is the core economic argument for detection-assisted inspection documentation. It is not a claim that the judgment can be automated. It is a claim that the mechanical steps can be, and that concentrating engineering time on judgment rather than mechanics produces a better quality of compliance documentation at a lower cost per asset.
Where This Leaves the Documentation Budget
A detection-assisted workflow does not eliminate the documentation engineering cost. An engineer still reviews detections, verifies significant findings, applies condition ratings, and signs off the final report. Those steps require expertise and cannot be skipped. But the hours required for those steps are substantially less than the hours required for manual footage review and anomaly logging.
In our early-access pilot programmes, the post-detection engineering time for report review and acceptance was in the range of 6 to 10 hours for a 25-foundation campaign, compared to 60 to 100 hours for manual footage review. The documentation phase cost per campaign is substantially lower, and the time-to-delivery is faster. The remaining engineering cost is concentrated on the steps where expertise is genuinely needed.
We are not suggesting operators should expect to eliminate documentation costs entirely. That expectation would not be realistic, and it would not produce good outcomes. Compliance documentation requires professional engineering accountability that has to be backed by engineering time. What is achievable is shifting the allocation of that time from mechanical watching-and-logging to expert review and judgment, which is a better use of limited and expensive inspection engineering capacity.
