The tidal "Rule of Twelfths" in surfing
How many times do you get perfect wind and wave conditions, but, frustratingly, the tide is too low or too high to surf? Learn the Rule of Twelfths and select the right time to go surfing.
Tides are a key factor when it comes to surfing and wave riding. Tide height affects the volume of water; or the depth of water and breaking of waves.
If the tide is too high, incidences of closeouts increase, while if the tide's too low, waves can be mushy or slow-rolling. That is why we must adapt to tides to get the most out of a surf session.
The Rule of Twelfths is a rule of thumb for estimating the height of the tide at any given time. The rate of flow in a tide increases smoothly to a maximum halfway point between high and low tide, before smoothly decreasing to zero again.
This means that in the first hours of a tidal shift, you may notice that the tide might not rise/fall so much, yet the entire process will accelerate through the mid hours.
Tide times available on tide charts usually tell you the exact hour and minute of both low and high tide.
The Rule of Twelfths applies to the semidiurnal tide - a tide having two high waters and two low waters during a tidal day, which is exactly what happens in most locations.
The semidiurnal tide period lasts for a period of 12 hours and 25.2 minutes from low to high tide, and then repeats back to low tide again.
Learning which are the right moments to hit the surf - keeping in mind the Full/New Moons and First/Third Quarter Moons - will save you time and increase the quality of your session.