Blog 2: When is the Best Time to Surf?

When’s the right time grab your surfboard and hit the beach? High tides cause closeouts, which blocks a surfer’s path, and low tides cause slow-rolling waves, which are low frequency and high amplitude waves. Ideally, you want to surf during mid tide conditions. But first, what causes these changes in tide?

Tides are caused by the “differences in gravitational pulls of the Moon and Sun between near and far sides of the Earth,” (Pogge, 2007). However, the effect of the Sun’s gravitational pull on Earth’s tides are approximately 46% of the Moon’s effect on tides. This is because the Sun is 390 times further from the Earth than the Moon. Therefore, the difference of gravitational pull of the Moon from the near side to far side of the Earth impacts the tides the most. The effect is a “bulge” in Earth’s waters being pulled toward the Moon on the side in line with the Moon, or pushed away from the Moon on the far side of Earth. This causes high tide. High tide occurs every 12 hours as the Earth rotates 360-degrees in a single day. Additionally, since the Moon is orbiting the Earth, the times for high tides and low tides in a given location will change by 50 minutes every day.

During a New Moon or Full Moon, the tides are 20% higher in high tide regions and 20% lower in low tide regions. This is caused by the perfect alignment between the Moon, Earth, and Sun, causing extreme tides. Using “Rule of Twelfths” you can find the perfect time to go surfing.

In order to understand the “Rule of Twelfths,” we first need to understand the tempo of the tides. When the tide reaches the highest point, it slows down before changing directions into low tide. At its halfway point, the tides have reached its maximum speed. This maximum speed occurs two times a day as there are two high tides and two low tides in a day, approximately 6 hours apart from each other. In the first hour, the “water level rises by 1/12th of the total range,” (Carey, 2013) then rises by 2/12ths of the total tide in the second hour, then rises by 3/12th in the third and fourth hours, then 2/12ths the fifth hour, and lastly rises by 1/12th the sixth hour. The pattern is 1, 2, 3, 3, 2, 1. Clearly, during mid tide the rise is the fastest at 3/12ths in the third and fourth hours, which is how you can determine this is the best time to surf, avoiding closeouts from high tides and slow-rolling waves during low tides. Note that the “Rule of Twelfths” only applies to the semi-diurnal tide, a “tide having two high waters and two low waters during a tidal day,” which occurs in most locations.

To conclude, understanding the effect the Moon has on Earth’s tides during the day can allow someone to plan their perfect surf session. By applying the “Rule of Twelfths” to your understanding of the difference gravitational pull on Earth by the Moon, you can surf during ideal mid tide conditions.

References:

Pogge, Richard. “Lecture 20: Tides.” GPS and Relativity, The Ohio State University, 14 Oct. 2007, http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit4/tides.html.

“How Do the Moon and Sun Affect Tides and Surfing?” SurferToday, SurferToday, http://www.surfertoday.com/surfing/how-do-the-moon-and-sun-affect-tides-and-surfing.

“How Do the Moon and Sun Affect Tides and Surfing?” IndoSurfLife.com, 30 Sept. 2011, indosurflife.com/2011/09/how-do-the-moon-and-sun-affect-tides-and-surfing/.

Carey, Teresa. “Understanding the Rule of Twelfths for Tide Prediction.” Sail Magazine, 12 Apr. 2013, http://www.sailmagazine.com/cruising/understanding-the-rule-of-twelfths-for-tide-prediction.

4 thoughts on “Blog 2: When is the Best Time to Surf?

  1. Thank you for introducing the “Rule of Twelfths!” Although I’m not a good wave rider, it’s still good to know such a rule that applies to tides in most locations. Are there any patterns of other types of tide (for instance, in the Gulf of Mexico, there is only one high tide and one low tide each day)?

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  2. Very interesting to see tides used like this. I know that waves are important to surfing, but I honestly just never considered that the transition period(s) between high and low tide could be taken advantage of like this. Thinking about it, it makes sense that the midpoint between two extremes would be when there’s the highest rate of change (which translates to a higher slope/speed). I wonder how many surfers consciously take information like this into account when deciding to go out surfing, or if more of them just focus on the patterns without worrying about the ‘why.’

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  3. I really enjoyed the “rule of twelfths” you discussed in your blog post was interesting. Even though the question seems like one that science would have an answer for, I’d never thought about what exactly the rate of tide changes would look like. It’s also interesting that the resulting rule looks (at least somewhat) sinusoidal, given that everything involved (the Moon, the Earth, the strength of gravitational forces, etc) is relatively spherical. In terms of applying this, it seems unfortunately that the rate of change is so much higher during the ideal conditions (mid-tide) than it is when you wouldn’t want to surf (high/low-tide). I’d be curious to know, within the mid-tide, when the best conditions are, and if there’s any difference in how good the surfing is when the tide is receding vs. coming in.

    Great post!

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  4. Being someone who is balance challenged, I never considered the physics behind catching the best wave, so I really enjoyed this post. One thing that I found while researching my own blogpost that wasn’t really talked about here, is that even if the Sun were not involved in the System there would still be a high tide opposite the Moon which can be modeled by the differential force of gravity acting along the entire surface of the Earth. So, now I’m left considering in the complicated system if the time of month has a significant impact on the potential for a good wave the same way the time of day does.

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