July 4, 2022

Why a surfer needs to know how tides work

To learn how to surf well, every surfer must understand the ocean.

“Waves are the voices of the tide. And the tide is life itself. He brings food to marine life and takes out ships in the sea. He is the pulse of the ocean. “

Tamora Pierce

He must know what a swell is, where the waves come from, how the wind affects them, and much more.

There is knowledge about the ebb and flow of the tide among such knowledge.

To ride the best waves at the best time, you need to understand how the tide can change the locks, what water level is ideal for a particular spot, and when to expect that level.

In this article, we will figure out what the ebb and flow are, where they come from, what they are, what affects the tide level, and how to determine at what time what water level to expect.

Well, in the end, we will write what practical value tides have for a surfer.


First of all, it is the gravity of the Moon.

The main reason the water level in the world’s oceans rises and falls every day is gravity.

Since the Moon is closest to the Earth among all other celestial bodies, its influence is the greatest. In second place is the Sun.

And, although it is much farther from us than the Moon, the attraction of the Sun is still felt since it is much larger than any planet in the solar system.

However, the Sun’s gravitational force about the Earth is only 46 percent of the Moon.

Therefore, there is another celestial body, which affects the Earth; this is Venus! However, its gravity is only 0.001% of the solar gravity.

The force of gravity of the Moon and the Sun is called tidal force. It is not large enough to act on solid bodies (although its Moon can stretch up to 30 cm!).

However, water in the World Ocean lends itself to its significant influence, the liquid state of which allows the water level to change by several meters.


The Moon’s revolution around the Earth – lunar day – is approximately 24 hours and 50 minutes.

There is a half-day high tide; we have two high tides and two low tides during a lunar day.

Since the lunar day is longer than the Earth’s, the time of the ebb and flow shifts every day.

However, there are several places on Earth where water rushes in only once per day.

Such places are the South China Sea, the Gulf of Mexico, and others.


Many who have been on the ocean for more than two weeks noticed that the ebb could be influential some days, and it is not so noticeable on others.

The fact is that depending on the phase in which the Moon is now, the difference between the maximum When the full and new Moon, when the Sun during the full and new Moon, Moon, and Earth stand in one line, the difference is maximum.

This tide is called “syzygy.”

This phenomenon occurs because the tidal forces of the Sun and Moon add up.

And during the first and third quarters of the lunar cycle, when the Moon is half-illuminated by the Sun, the water drop will be minimal. This phenomenon is called quadrature tide.

The trajectory of the Moon and the Sun also affects the height of the tide.

The fact is that the Moon moves around the Earth, not in a circle, but in an ellipse.

Therefore, the Moon is closer to the Earth at one time, further away. Thus, a very high tide is observed when the syzygy ebb falls when the Moon is closest to the Earth (this happens once every 7.5 lunar cycles).

If the Earth also approaches the Sun as close as possible (its orbit also looks like an ellipse), the wave will be higher. It happens every 18.6 years.


You may ask, if the Moon attracts water only from one side, then why are there two ebb and flow per day on one side and the other side of the planet?

Honestly, this question haunted me until I read the excellent book Surf Science by Tony Butt.

The second flush comes from two factors. The first is the difference in the force of attraction of the Moon between one side of the Earth and the other.

The second is the centrifugal force that occurs during the rotation of the Earth.

It seems that everything should be clear at once with the first factor.

The Moon is closer to one side of the Earth than the other.

Therefore, it is logical to assume that the strength of gravity will differ. The way it is.

If we take the force of gravity of the Moon in the center of the Earth as a basis, then on its surface, which is closest to the Moon, the force of gravity of our satellite will be 3.4% greater than in the center, and weaker by 3.2% on the opposite side of our planet.

Now let’s talk about the second factor. What is the centrifugal force, and where does it come from.

Above, I mentioned the rotation of the Earth, but I did not mean its rotation around its axis, but rotation around the Moon.

Most of us know from school that the Moon revolves around the Earth. But they both revolve around the common center of their mass, which is located at a distance of 4.5 thousand kilometers from the center of the Earth.

This center is situated in the radius of the Earth, which is just over 6.3 thousand kilometers. Consequently, the Earth and the Moon revolve around this center at the same speed.

Imagine that you put a hair tie on your pencil and start twirling it. The elastic will stretch across the movement. Roughly the same thing happens with water on Earth.
Due to this rotation of the Earth around the Moon, a centrifugal force arises that pulls ocean water from the Earth.


If you have been to the coasts in different countries, you may have noticed that somewhere the low tide is very noticeable, for example, in Bali, and somewhere the water level during high and low tide is almost the same, for instance, in the Maldives.

Now we know that the gravitational force of neither the Moon nor the Sun changes significantly; that is, in one place on the surface of the planet, the highest tide and minimum ebb tide will always be approximately the same.

However, with all this, somewhere, the low tide height is half a meter, somewhere three, and somewhere as much as sixteen.

The reason for this is the bottom topography. The tide can be viewed as a giant wave. If you remember where the lock comes from – it starts to rise when the depth becomes less than a particular mark – then it becomes more and more apparent.

Accordingly, the height of the tide depends on the depth of the ocean. The shallower the depth, the “higher” the tidal wave becomes, and the more significant the difference between the maximum water and the minimum becomes.

If there were no land on our planet, only two tidal waves would move around the Earth. However, due to the continents and the complex shape of the ocean floor, there are more tidal waves.

Take a look at the map. Places with different tide heights are highlighted, where dark red is the maximum height and blue is the minimum.

The points where the white lines converge are called amphidromic. In them, the difference between ebb and flow is zero. The farther from this point, the higher the amplitude of the tide fluctuation.

A black arrow can be seen near these points; it shows the tidal wave’s direction. The white lines delineate the zones where the tide is in the same phase, with a difference of a little more than an hour between each line.

There are twelve such phases around each point. The time of passage of a tidal wave through all these zones is equal to half a lunar day.


The above may seem too complicated to describe these movements with mathematical formulas. It isn’t easy, but possible.

Thanks to these formulas, the height of the ebb and flow can be calculated for many years to come. Each port contains unique tables or graphs called tide charts. Below you will find two types of tide charts.

In the first variant, the horizontal axis marks the days of the month, and the vertical axis denotes the hours in a day.

The intersections of the columns show the water level for that particular day and for that specific hour.

The second option is taken from the magicseaweed.com surf forecast site, familiar to all surfers.

Here the tide is shown by a graph, next to which the maximum and minimum water times are indicated.


Surfers need information about the water level in the ocean or sea to understand whether the desired spot will work simultaneously and how it will do it.

It is because the nature of the wave depends on the depth of the water at the site. The larger it is, the flatter and slower the wave becomes—the shallower the depth, the sharper and faster the wave.

Accordingly, in places where ebb and flow are noticeable, the nature of the lock at the spot will vary quite a lot depending on the water level.

Thus, some waves can only work at low tide because it is too deep there for the lock to rise at high tide, and some – only at high tide because it is too shallow there.

Take, for example, the spot Kudet in Bali. With an average swell level, you can usually surf here only when the water level is less than 1 meter.

In this case, the best waves will be on the minimum water at low tide. At maximum water, the lock generally ceases to rise there.

But in the Philippines, on the island of Siargao, at cloud 9, when there is a lot of water, the wave remains sharp and even slightly trumpets.

And when the water pours out, the depth becomes waist-deep, and then the tide begins to trumpet very vigorously, becoming super-fast and dangerous.

Therefore, if you ride on a new spot, first find out about the water level where the best waves are.

This information can be found on the Internet at one of the many sites with descriptions of spots or locations on the shore from experienced surfers.

Another factor influenced by ebb and flow is currents.

The greater the water drop, the faster it comes and goes; the winds become more muscular.

At the same time, the maximum speed of currents falls in the middle of the period between ebb and flow.

So, for example, if today the minimum water is at noon, and the maximum is at 6, then in the interval between 2 and 4 p.m., the water will pour out the fastest, and the flow rate will be higher.

And during the change of water movement, the current slows down at 12 or 6 o’clock.In addition, there is a belief that the waves get better when the water level rises.

They say that the movement of water during high tide is directed in the same direction as the waves, and therefore they are smoother.

Conversely, when the water is pouring out, the waves become worse. No reliable scientific data confirms this fact; however, often, waves are better on tidal water.

I hope this article was helpful to you, that you have learned a little new and that this information will help you choose your time with the best waves!

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