Four numbers decide whether a turbine turns tomorrow
- What it is
- The significant wave height at which crew transfer from a crew transfer vessel stops being routine. Above it, the day is a stand-by day. Some vessels are rated to 2.0 m.
- Where it comes from
- Industry review of CTV transfer safety in Ocean Engineering, 2026; ABPmer.
- Why it matters
- It is a hard edge, not a preference. Everything else on this page — the crews, the fleet, the coordination room, the forecast cycle — exists to get work done on the correct side of that number.
- What it is
- Technical availability guaranteed under a long-term service contract: the share of the time a turbine is able to produce when the wind is there.
- Where it comes from
- Turbine manufacturers’ long-term service agreements, as reported by Windpower Monthly.
- Why it matters
- It converts maintenance from a cost line into a product. Three per cent of a year is eleven days. That is the whole argument.
- What it is
- The share of the levelised cost of energy of an offshore wind farm that goes to operations and maintenance across its life.
- Where it comes from
- Industry cost reviews.
- Why it matters
- Building a farm takes three years. Keeping it running takes thirty. A quarter of the lifetime cost sits in the phase nobody photographs.
- What it is
- Weather-workable days a year in the southern North Sea: about 219 (60 %) for a crew transfer vessel, about 285 (78 %) for a service operation vessel with a motion-compensated gangway.
- Where it comes from
- Offshore Industry O&M review, 2026. Industry estimate — typical regional figures, not a measurement of any one site or year.
- Why it matters
- Sixty-six days is the difference between the two vessel classes. That difference is what a walk-to-work vessel is actually sold on.
Pull the wave height and watch the working year change shape
This is the number every offshore maintenance plan is built on, and it is the only one the operator cannot negotiate.
days the sea sits below it
The slider moves the limit of the vessel, not the weather. Two points on it are taken from the industry: a crew transfer vessel stops at about 1.50 m and gets roughly 219 workable days a year, a service operation vessel with a motion-compensated gangway works to about 2.50 m and gets roughly 285. Every other position on the slider is our own interpolation between those two, drawn to show the shape of the problem.
This is an illustration, not a forecast. It uses southern North Sea industry estimates and one smooth curve. A real weather window is decided by wave period, wind, visibility and the length of the job, not by wave height alone. Nobody should plan a mobilisation from this control.
The market these numbers sit in
Ørsted, PGE, Orlen, Equinor, Vestas and Siemens Gamesa appear here because they built the market these numbers describe. None of them is a KELDVIK client. KELDVIK does not have clients — it is a concept.
Sources. 1.50 m CTV transfer limit — 2026 review in Ocean Engineering, ABPmer. 97 % technical availability — manufacturers’ long-term service agreements via Windpower Monthly. 20–30 % O&M share of LCOE — industry cost reviews. 219 / 285 workable days — Offshore Industry O&M review 2026, industry estimate. 39 GW Europe and 2 GW connected in 2025 — WindEurope. 92.5 GW world — GWEC Global Wind Report 2026. Baltic Power project data — Orlen / Northland Power. V236-15.0 MW geometry — vestas.com. GWO and IRATA validity — GWO standard, heightec, Dangle Academy. Figures we could not confirm at first hand are not on this page: the cost of an hour of turbine downtime, V236 hub height, DNV standard numbers, and weather losses specific to the Baltic. KELDVIK’s own numbers are invented.