Frequently asked questions
How Isobath works, where the numbers come from, and what we don't promise.
Is Isobath free?
Yes. The site is funded by discreet Google ads (never on safety pages), whose cookies are only used with your consent. A free account only keeps your favourites and alerts across devices.
Where do the forecasts come from?
From eight public numerical models (Météo-France, ECMWF, NOAA, DWD) served by Open-Meteo, checked against Cerema's CANDHIS buoys. Every figure is dated on the Method page.
Why a range and not a single number?
Because models never fully agree, and the size at the shore depends on the seabed and the tide. An honest range beats a falsely precise number.
Offshore swell vs size at the shore?
Offshore swell is what models and buoys measure. As it reaches a rising seabed, the wave slows, steepens and breaks: Isobath estimates that breaking height, spot by spot.
Are the forecasts reliable?
Very close to reality 1–2 days out, less after that. The confidence index says so for each hour, and the Accuracy page shows our real errors against buoys.
Are tides and coefficients official?
They are estimates calibrated on SHOM tide tables (about 10 minutes for times, 1–2 points for coefficients). SHOM's official tables prevail.
Are the webcams live?
Isobath hosts no cameras: we link to the operators' official pages after checking that they respond.
How can a spot be added?
Write to us from the Press & partners page: each spot needs a verified orientation, seabed and settings before it appears.
Can I show the forecast on my site?
Yes, for free: the Press & partners page gives the widget code for each spot.