Is there a tide app that works fully offline with no signal?

Working out the tide with no signal, app or not

1. Load the week before you leave signal. At home, screenshot or print the next seven days for your station. A photo needs no bars.
2. Note the station and the datum. Heights only mean something against the datum printed at the top (MLLW, chart datum).
3. Estimate the height between the printed times with the rule of twelfths. In the six hours from high to low water, the tide moves roughly 1/12, 2/12, 3/12, 3/12, 2/12 and 1/12 of the range each hour.
4. Test your app in airplane mode before you trust it. Many tide apps quietly fetch from a server. Switch off data and see whether the curve still draws.
5. Watch the real water line against a fixed mark. A rock or a step shows whether the prediction is running early or late that day.
6. Carry paper. It never runs out of battery.

How ShoreWindow does it

Tide, sun and moon are computed on the device from published harmonic constants for 5,740+ coastal stations across 108 countries, so it is not a one-country app. First light, sunrise, both golden hours, sunset, last light, moon phase and moonrise are all worked out on the phone. Alerts are scheduled on the device too, with no server watching your shore. Only the weather card needs a connection: air, wind and wave height where the forecast reaches, and water temperature where a gauge measures it. You can switch those lookups off.

Every height says where it came from: the station, how far away it is, its datum, its provider and when the data was imported, plus a confidence tier in plain words. Sources are CC-BY licensed, including NOAA CO-OPS, Kartverket, LINZ, DMI, MET Norway and Queensland DTMR, and sixty-three stations are individually checked against published tide tables.

The free tier does not expire: one saved shore, seven days of tables, curves and windows, and one alert. ShoreWindow Pro is $14.99 a year with a 7-day free trial, $2.99 a month, or $39.99 once for a lifetime unlock. Pro adds unlimited saved shores, the 30-day window board paged forward a year, a Finder across every shore and every day, recurring alert rules, calendar export and widgets. Prices are in US dollars and vary by country.

ShoreWindow runs on iPhone, iPad and Android phones and tablets. It is live on Google Play now, and the iPhone and iPad version is with the App Store for review. There is no Mac, Windows or Apple Watch version. No account, no login, no cloud sync: your saved shores stay on your phone, with no ad SDKs and no usage analytics.

Predictions are modelled and not for navigation. ShoreWindow does not assess access or sea safety. Always use your own judgement and local conditions.

Get ShoreWindow

• Google Play
• App Store: not yet. The iPhone and iPad version is in App Store review.

Related questions

Do ShoreWindow alerts work without signal?

Yes. Alert scheduling happens on the phone, not on a server.

Which part of ShoreWindow needs a connection?

Only the weather and wave forecast. Tide, sun and moon run on the device, and you can turn the weather lookups off.

Does offline mean my data is stored on the phone too?

Yes. There is no account and no cloud sync. Saved shores and rules stay on your phone.