New: official ADMIRALTY tide-state information in Passage Planner
Published 2026-05-06
One of the bits of feedback I’ve had since launching Estuary Forecast Passage Planner is that people would like more tide information built directly into the planning view.
That makes complete sense. When you are planning a coastal passage, the tide is not just a nice extra — it can affect when you leave, how long the passage takes, what conditions you might expect, and whether your arrival window looks sensible.
So I’ve added a new tide feature to the Passage Planner.
When you create a passage with a start point, end point, departure time and calculated ETA, the app can now look up the nearest official ADMIRALTY tidal station to both your departure point and arrival point. It then shows the tide state for those parts of the plan: whether the tide is rising or falling, along with the surrounding published high and low water times and heights.
The idea is simple: give you useful tidal context inside the passage plan, without pretending the app knows more than it really does.
What the new feature does:
It automatically finds the nearest ADMIRALTY tidal station to your departure and arrival points. It shows whether the tide is rising or falling at your planned departure time and ETA. It also shows the nearby published high and low water events, including times and heights.
What it does not do:
It does not calculate the exact tide height at your precise waypoint. It does not interpolate a tide height for the exact time of your passage. It does not show tidal streams. It does not show a continuous tide curve. It also only covers today and the next six days on the current API access.
ADMIRALTY offers a few different tidal API options. The Discovery API, which I’ve used for this first version, provides current day plus six days of tidal events for UK tidal stations. It is a free one-year subscription, but it only provides high and low water event information rather than full tidal curves, tidal streams, or exact predicted height at a specific time and place.
The paid tiers go further. The Foundation API provides current tidal information plus 13 days of tidal height and stream events, with 20 calls per second, 20,000 calls per month, and is listed at £120 per year excluding VAT!! The Premium API goes further again, offering historical data, current plus one year of tidal events, interval predictions, tidal stream events and rates, 100 calls per second, 100,000 calls per month, and is listed at £300 per year excluding VAT!!! ADMIRALTY also notes that the paid Foundation and Premium tiers add tidal stream and tidal height graph capabilities.
For now, I’ve chosen the Discovery API because it lets me add a genuinely useful official-data feature without immediately adding a recurring cost to the service. Full tidal streams, exact-height lookups and proper tidal curves are absolutely the kind of thing I’d like to add in the future, but that needs one of the paid tiers, so I’ll need to see how the service grows before committing to that.
That distinction matters. I would rather the app be clear and honest than give a false sense of precision. So the wording in the app makes it clear that the tide state is based on the nearest official ADMIRALTY tidal station, not the exact route coordinate.
Hopefully this makes Passage Planner more useful when sketching out a route and sense-checking a trip. It is not a replacement for proper navigation, official charts, tide tables, notices to mariners or good seamanship — but it should give you another helpful piece of information in the same place as your route, waypoints, bearings, ETA and weather.
As always, I’d love to hear what you think. If you use Passage Planner for a real route, let me know how the new tide information feels and what would make it more useful.
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