The Secret of 'Fluid Dynamics' and 3 Breakthroughs to Make Water Your Ally, Which 99% of Swimmers Don't Know

Hello everyone, it's Yoshi, the Flipper President!

"You're swimming, but you don't know fluid dynamics?!"

This is something that often surprises me when I'm on the pool deck.

Try to remember your swimming lessons.

"Yes, kick harder!"
"Make your hand movements bigger!"

Many of you have probably heard instructions like that. But almost no one can explain the reason why you should do that. That's why there are so many coaches who don't even realize they are giving the wrong instructions...

This is a very serious problem.

Because, if you are swimming or fin swimming without knowingfluid dynamics, it's like driving a car without knowing how the engine works.

I think it's practically a "sin".

That said, this is a subject you rarely have the opportunity to study in school. Even I, who have been speaking so arrogantly, didn't know the details at all until I studied it in graduate school, sorry haha.

Today, let's take a peek at this "science of water"!
It should definitely change the way you interact with water.

What is 'Fluid Dynamics' in the first place? - The science that unravels the mysteries of water

What exactly is 'fluid dynamics'?
I think some of you might not know, so I'll let you in on a secret first.

It sounds like a difficult term, but it's actually a science that is very close to us.

First, "fluid" is a general term for things like liquids and gases whose shape changes freely.
Water is of course a fluid, and air is also a type of fluid.

And "dynamics" is the study of the relationship between the movement of objects and forces.

In other words, fluid dynamics is the "science concerning the movement of water and air".

The reason airplanes can fly in the sky and ships can travel across the sea is all because of the principles of fluid dynamics.
And the reason humans can swim underwater is also thanks to this science.

Have you ever felt resistance when walking against the wind?
Have you ever had an umbrella turn inside out in a strong wind?
Have you ever felt the strong water pressure of a shower?

All of these are phenomena of fluid dynamics!

How about that?
Isn't fluid dynamics closer to you than you thought?

Making a science out of 'water resistance'

Now, let's get back to talking about the pool.

Have you ever walked in a pool?
Of course you have.

Have you ever run in a pool? I'm sure you have.

So, why is running so many times harder when the movement is almost the same?

This is where an important secret of fluid dynamics is hidden!

In fact, when your speed doubles, water resistance quadruples.
At triple the speed, a staggering nine times the resistance is generated!

This is a fundamental law of fluid dynamics established by the research of the famous physicist Osborne Reynolds. This forms the basis of modern swimming theory.

Here is an experiment I want you to try.

The next time you are in a bath or pool, try moving your palm slowly through the water.
And then, what happens when you perform the same movement quickly...?

You will surely be surprised by the difference!

So, why does this phenomenon occur?
To understand that, you need to know the true nature of 'water resistance'.

I will explain it in a little more detail.

Three types of resistance determine your swimming and your times!

You might hear or say things like 'try not to get resistance...' or
'reduce water resistance as much as possible...'

You probably hear or use the word 'resistance' casually in the field, but there are actually different types of resistance.

Since it's just one word, many people might think they are all the same...? You have to think about countermeasures for each one, not just one type, so I will explain them in order.

1. Pressure resistance (form drag)

When you try to move through water, you have to push the water in front of you out of the way. At this time, it becomes difficult to move forward because the water hits the front of your body, and this force of the water is 'pressure resistance (form drag)'.

Let's imagine this with air instead of water.

On a day with strong rain and wind, there are times when a gust of wind hits you from the front along with driving rain, right? Have you ever held an open umbrella in front of you at those times?
If you try to walk forward like that, the wind hits the umbrella and becomes as heavy as a wall, making it hard to move forward. This is pressure resistance.

The same thing happens in water. Moreover, since water is hundreds of times denser than air, you experience significant resistance even with an area the size of a human palm, rather than a large area like an umbrella.

In this way, pressure resistance is greatly influenced by the 'shape' facing the front.
That is why athletes adopt a gliding posture called a streamline while underwater.

2. Wave-making resistance

Wave-making resistance (vortex resistance) is 'the force of the vortex created behind your body as you move forward, which pulls you backward'.

For example, remember when you are waiting at a traffic light.
When a car passes by at high speed, you feel a gust of wind right after it, right?

That wind generated behind the car is also a vortex of air. And actually, the car is being pulled by that vortex, which hinders it from moving forward. Because the car has so much power, you rarely feel this when riding or driving... but when a person swims, this has a very large impact.

In the same way, when you are swimming in a pool, a water current is generated behind your body, pulling you and constantly hindering you.
Applying this to the previous example, the 'car' is you, and the 'wind' is the wave.

Moreover, the faster you swim, the larger this rear vortex becomes, making it increasingly difficult to move forward. It's like the feeling of being pulled back by a rubber band the further you go.

Even in the vehicle example, the strength of the wind following it changes depending on the speed of the vehicle that passed in front of you, right? Try to imagine the following for each:

So what should you do?

The answer is to move smoothly without disturbing the water as much as possible so that extra vortices are not created. In terms of imagery, it is good to keep in mind to 'move your hands and feet so as not to churn the water'.

Even in dolphin kicks or fin swimming, 'excessively large undulations or overly strong kicks actually increase resistance and waste energy'.

3. Frictional resistance

The sensation of water clinging to your skin is frictional resistance. Resistance is generated on that 'surface' where the water and skin are in contact.

For example, when you stroke the surface of paper with your finger, regular paper versus sandpaper, it is harder to slide your finger on the rough sandpaper compared to the smooth regular paper, right?

When translated to underwater, this 'friction between water and skin' becomes a hidden brake when swimming.

That is why, to swim even a little faster...
✅ Shave body hair
⇒ Make the skin surface smooth to reduce friction!
✅ Wear a racing swimsuit
⇒ Use materials that do not disturb the water flow to minimize frictional resistance!

Just by making this adjustment, you can reduce drag in the water and swim faster and more easily!

The friction that occurs between the surface of your body and the water creates surprisingly significant resistance.
That is precisely why competitive swimmers shave their body hair and wear specialized swimsuits.

The common sense changed by fin swimming

These three types of resistance have an even more dramatic impact in fin swimming.

In regular competitive swimming, even Olympic athletes reach speeds of about 8 km/h.
However, in fin swimming, you can reach speeds of nearly double that, around 13 km/h.

As I mentioned at the beginning, if the speed doubles, the resistance quadruples.
In other words, in the case of fin swimming, where you reach nearly double the speed, you are fighting about four times the resistance of competitive swimming.
This battle against resistance is the very essence of fin swimming.

My mentor, 1972 Munich Olympic gold medalist Nobutaka Taguchi, learned through self-study since he was in junior high school and created the 'Taguchi Kick,' which became the prototype for the modern breaststroke.

From him, I learned about this fluid dynamics not only from swimming but also from a wide range of genres, such as ship hull shapes and the Birdman Rally.

In fact, I incorporated the hints I gained from those into my swimming, tried changing how I clasp my hands, modified my fins, and did various experiments! It was interesting because there were so many discoveries, haha.

"How much speed can I generate?"
"How much power can I produce?"

These are of course important, but more than 90% of people are obsessed only with those, and I think there are too few people thinking about how to minimize resistance and how to swim efficiently.

So, please, in your next practice, try focusing thoroughly on low resistance rather than power output. You will surely gain a new weapon, and you will be able to get ahead of those around you!

In conclusion

"It is a sin not to know fluid dynamics"

The reason I stated that at the beginning—I think you can understand it painfully well now, can't you?

Understanding the essence of water is the first step to swimming faster, more beautifully, and more efficiently.
And that should bring value beyond just improving your records.

Next time, I would like to share how to incorporate this theory into more practical training!

So, thank you for reading this far this time as well.

If you thought this content was good or learned something from it, I would be happy if you could support me with a 'Like❤️', 'Follow✅', 'Share♻️', and 'Tip💙'!

Also, I will continue to post content that will be useful to all my readers through introductions to training and explanations of swimming that you can't hear anywhere else, so please enter your 'questions or things you are curious about' in the 'comment section' and let me know!

See you next time!
Bye for now!

Fin Swimming Specialist
Finhin President Yoshihide Sekino

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