Tide and surf: the window that actually works

The UKHO gives you tide times for free. So does NOAA. We are not going to sell you a tide table.

What a tide table does not tell you is when your break actually works. That is a different question, and on a coast with seven to ten metres of range it is the only one that matters.

Why the time is not the answer

Two high tides a day, roughly, and each one about fifty minutes later than the last. Which means the window that worked at seven this morning is at about ten to eight tomorrow, and by the end of the week it has walked itself out of your morning entirely.

That is the part people get wrong. They learn that their break works on a pushing tide, check the tide time, and then find the sandbar dry or the wave closing out, because the tide is only one of three things deciding the session.

The three things, in order

The state of the tide, not the time. Most breaks have a band that works: two hours either side of low, the first half of the push, the last hour before high. That band is a property of the sandbank or the reef, and it does not change day to day.

The range. This is what a tide table hides. A three-metre range and a nine- metre range produce completely different sessions at the same stated tide state, because the water is moving at a completely different speed. On springs the push is fast and the window is short. On neaps it is slow and the window is long but weak.

Springs and neaps. New moon and full moon give springs, the big ranges. The quarters give neaps. Roughly a fortnight apart, and the difference on a British coast can be several metres. If you only learn one thing about tide and surf, learn which one you are in this week.

Where swell and wind come back in

A perfect tide window with a cross-shore wind is a wasted alarm. The tide opens the door, the swell and the wind decide whether there is anything behind it.

That is why a tide app and a surf app answer different questions, and why neither one alone gets you out of bed for the right reason.

What we do with this

Sendoa puts the three together and makes the call for each spot: Worth it, Maybe, Not today or Big for you, with the window and the reasons. No tide table to interpret, no score out of five.

The tides are recomputed on the phone itself, from public harmonic constants, so they work with no connection. And we publish our error against real tide gauge records, port by port, the bad ones included: nine of nine UK ports within eight minutes against a month of readings. The full table is here. We do not know of anyone else who publishes their errors.

Frequently asked

Is high tide or low tide better for surfing? Neither, in general. It depends on the bank or the reef. What is general is that the window moves about fifty minutes later each day and changes length with the range.

What is a spring tide? The larger range around new and full moon, when the sun and moon pull together. Bigger range, faster water, shorter window.

Does the tide matter less on a big swell? It matters differently. A bigger swell can make a break work on a tide state that is usually too full or too empty, which is exactly the case where a single rule of thumb fails you.

Do I need a connection? For the tide, no. It is computed on the device. For swell and wind, yes, those come from a forecast.