What tide is best for surfing? Tidal range and timing explained

A tide is the ocean rising and falling under the pull of the Moon and, to a lesser extent, the Sun. On the Atlantic coast of Europe the rhythm is steady: two high tides and two low tides a day, roughly 6 hours 12 minutes apart. Because the lunar day runs slightly longer than 24 hours, tide times slide about 50 minutes later each day — today's 9am low water is tomorrow's 10am.

Two words worth knowing: the flood (water rising towards high tide) and the ebb (water draining back out).

What the tide changes is not the swell itself. It changes the depth of water over the bottom — and it is the bottom, whether a sandbank, a rock shelf or a coral reef, that makes a swell break. Change the depth and you change where the wave breaks, how steep and fast it is, and sometimes whether it breaks at all.

Tidal range is the height difference between low water and high water on a given tide. Around new moon and full moon the Sun and Moon line up, the range is at its biggest, and you get spring tides — nothing to do with the season. Around the quarter moons the range shrinks: those are neap tides. In France the same idea is published as a tide coefficient between 20 and 120, where roughly 45 is a neap, 70 an average tide and 95 or more a big spring.

The bigger the range, the more water has to move in six hours:

• currents pull harder, especially around mid-tide;
• the level changes fast, so your window of good conditions closes sooner;
• a spot can go from working to unsurfable inside an hour.

One genuinely useful shortcut is the rule of twelfths: over the six hours of a tide, the water moves about 1/12 of the range in the first hour, 2/12 in the second, 3/12 in the third and fourth, then 2/12 and 1/12. So the level barely moves around high and low water — that is where you get time. At mid-tide it races, and the currents race with it.

Range is also local. On the French and Portuguese Atlantic it runs to several metres and the tide dictates the session; in the Mediterranean it is a few dozen centimetres and you can largely ignore it.

On a beach break the bottom is sand, shaped into banks that shift with every swell and current. At low tide there is little water over them: the wave jumps up suddenly, gets hollow and fast, often closes out, and the shore break lands hard on the sand. At high tide the same bank sits under deep water: the swell rolls over it without breaking, or breaks weakly right on the beach. Hence the most common rule of thumb — mid-tide, rising or falling, is the best compromise on most beach breaks, and the most readable playground while you are learning.

On a reef or point break the bottom is fixed. The question is no longer where it breaks but whether there is enough water. Plenty of reefs need a minimum depth, otherwise you are surfing centimetres above rock, coral or sea urchins: at low tide that is not the same session, it is a different risk. Others only wake up at low water, when the wave stands up on the shelf. Every reef has its own rule.

To find your spot's rule: read the spot guide, ask locals or the surf school on the beach, and above all watch — go and look at the same wave two hours apart. On Yosurf, the per-level score and the day's best window tell you when swell, wind and time of day line up for you.

In practice, think in three-hour windows: about ninety minutes either side of the tide that works at your spot. That happens to be the length of a session.

As the sea drops, all the water piled up near the beach has to get back out, and it takes the deepest route available. That is how rip currents form — and, on the French Atlantic coast, the baïnes.

A baïne is a bowl scooped out between two sandbanks. It fills at high tide, then drains through a narrow channel as the sea falls: out of it comes a lane of water heading offshore, sometimes faster than you can swim. Baïnes are especially dangerous in the two hours either side of low water, and more so on a big tidal range.

A rip usually shows as a darker, calmer strip of water between two areas where waves are breaking, often with foam or churned sand streaming seawards. That inviting flat patch is the trap: it is exactly where the water is leaving.

If a current takes you:

• keep your board — it floats and it makes you visible;
• do not paddle straight against the flow, you will lose;
• move out sideways, parallel to the beach, then come back in with the breaking waves;
• raise one arm and signal if you cannot get out.

While you are learning: surf between the lifeguard flags, walk away if you cannot read the water, and never mistake a hollow low-tide bank for the same wave in a smaller size.