Tidebook — Support

Questions people ask

Does Tidebook work without a signal?

Yes, and that is the point. The app carries NOAA’s tide data for 3,489 stations (1,251 with their own harmonic constants and 2,238 corrected from a nearby reference station) and works the tide out on your iPhone. Free shows today and the next 7 days; Tidebook Pro opens any date, past or future. Only the map background, the live sensor level, the Conditions card and the weather-service alerts need a connection.

Why is my station not the closest one to me?

Tidebook picks the nearest NOAA station and shows the distance so you can see it. If it is not the one you want, tap the arrows at the top right, or open the Map tab and tap another one. NOAA has 3,489 stations but not one on every beach.

The times look off by an hour.

Tidebook always shows the time zone of the station, printed under its name, not the time zone of your phone. Hawaii, Puerto Rico, the US Virgin Islands and Guam do not use daylight saving time, and Tidebook knows it.

What does MLLW mean?

It is the reference the height is measured from: the average of the lowest daily tides. It is what United States nautical charts use, which is why it is the default. You can change it in Settings on reference stations that publish other datums.

Why does one station say “highs and lows only”?

Of NOAA’s 3,489 stations, 2,238 are subordinate: they do not have their own harmonic constants, only offsets from a nearby reference station. For those, Tidebook shows the highs and lows exactly, and draws the curve between them by interpolation. It tells you when that is the case, and which station it came from.

I paid for Pro and it is gone.

Open Settings inside the app, tap Tidebook Pro (the first row) and then Restore purchase. Pro is a one-time purchase tied to your Apple Account; reinstalling the app or changing iPhone does not lose it.

Will there be a subscription?

No. Tidebook Pro is one payment. If you bought it, you will not be charged again.

Can I use Tidebook to navigate?

Tidebook is a planning tool. It does not replace a nautical chart, and its predictions do not include wind, barometric pressure or river flow, which can all change the real water level.

Data

Tide data from NOAA CO-OPS, public domain. Tidebook is not affiliated with NOAA. Map by Apple Maps.

Privacy

Tidebook collects no data.