About Slackwater
Slackwater puts the tide for the places you fish, surf, and boat on your phone, and keeps it there when the signal drops.
Why we built it
A day on the coast runs on the tide. The low decides when a flat drains, when a boat ramp has water, and how long you have before the walk back from a sandbar floods. The tide apps we tried were free but went blank without a connection, which is exactly what happens at the water's edge, or they came bundled with a social fishing network that costs $79.99 a year.
We wanted something quieter: the curve and the times for your own spots, the solunar bite next to them, and the wind and water you plan around, in a fast app that asks nothing of you.
How it is built
Every tide in the app is computed on your iPhone. In the US it starts from NOAA's harmonic constants for 781 stations, in New Zealand from LINZ's for 45 ports, in Europe from constants fitted to the national agencies' gauge records at 140 stations, and in Japan from constants fitted to the Japan Meteorological Agency's tide tables at 239 stations. The solunar windows come from where the sun and moon are. None of that needs a connection, so the curve, the times, and the bite rating keep working offline.
A few things do use the network: marine conditions from NOAA buoys and wind alerts (Premium, US stations), the live water level where a national gauge publishes one, and JMA's sea temperature and warnings in Japan. Each request goes through a small proxy that passes a tide station's coordinate, never your location, and stores nothing.
Your spots, settings, and logs stay on your device and in your own iCloud. There is no account, and no server of ours holds your data.
The predictions have limits. Wind and air pressure move real water, which is why the live gauge can sit above or below the prediction. The bite rating is a way to rank your available days, and it promises nothing about fish.
What we will not do
- Ask you to sign up. There is no account to make.
- Show ads, track you, or sell your data. The app has no analytics or crash-reporting SDK, and its App Store privacy label reads Data Not Collected.
- Charge for the basics. The tide curve and times for up to three spots, the bite rating, and offline use are free. Premium adds alerts, marine conditions, two-week planning, and unlimited spots for $24.99 a year with a 7-day free trial, or $69.99 once (US prices).
- Call a crossing safe. Tide windows count down to when you should leave a sandbar or causeway, but they never say a crossing is safe, so follow local signs and official crossing times.
Who runs it
Slackwater is made by Handler Labs LLC, an independent software studio. Questions, a station that looks wrong, or a feature you want: write to support@handlerlabs.app.
Keep reading
How it works
How the tides and the bite windows are worked out.
Pricing
What is free and what Premium adds, with prices by country.
Privacy
Exactly what leaves your phone, and why.
Predictions are estimates for reference only. They are not for navigation or life-safety decisions. Always consult official tide tables (NOAA's in the US) and nautical charts.