Sail and sound

Sail and Sound
Sail (Travel photo created by senivpetro -

 उस छोर से परे क्या था, मालूम नही...

आसमान कि उचाइयां समींदर की गहराईयोंसे मिलती भी होगी? मालूम नही...

अनजान हम थे के उस पार कोन है? मालूम नही...

अनजान वोह थे के इस पार हम है, उन्हे मालूम नही...

तुफानसी लहरोंसेही तो इश्क था, इश्क से रूबरू होने हम निकल पडे...

हाथी के सामने बेखौफ चीटी कि तरह कश्ती लिये, हम निकल पडे...

जिग्यासा से शापित थे या फिर उपहारीत हम, क्या खोजने निकले? मालूम नही...

हम समंदर के सिकंदर थे, या कोइ सरफरोशी पागल, मालूम नही...


What was hidden beyond the horizon, was unknown...
Whether the expansive sky met the sea in its depths, was unknown...
Were we unaware of who lived on the other side?
Our love for the stormy waves led us to tread the unfamiliar path...
Or were they oblivious to us all?
Like an audacious ant staring into the eyes of an elephant, we raise our sail to fearlessly brave the winds and waves of the sea.
Whether the courage of our curiosity was a blessing or a curse, was unknown...
Were we the warriors of the sea or reckless adventurers, who's to say?
- Translated by Radhika


  • Author: Nikhil Chandratre
  • The first inspiration for sailing.
  • History of sailing
  • Mystics of Physics behind sailing
  • Can a boat sail faster than wind?
  • This week in Invisible History: Tomorrow is eleven days after. Domain: History.
  • Discuss the article here.

I wonder what could have inspired a human to explore what he could not see beyond the sea. I imagined and wrote the above poem on the same. I believe this must have been the exact feeling of someone who tried sailing for the first time in human history. Curiosity with which humans are either cursed or blessed made him ‘a genius’ to sail and go beyond the horizon.

Sailing has a massive history of its own. ‘La Santa María’, alternatively La Gallega, was the largest of the three ships used by Christopher Columbus (first European to discover America) in his first voyage across the Atlantic Ocean in 1492, the others being the ‘Niña and the Pinta’1. ‘São Gabriel’ was the ship with the help of which Vasco da Gama, a Portuguese explorer visited India for the first time in medieval history2. The fact is that sailing began in ancient times.

The first voyage

The question ‘who built the boat first?’ is quite difficult to answer because sailing predates writing and the material used to build the boats was obviously wood which has a short life span. The earliest historical evidence of boats is found in Egypt during the 4th millennium BCE. A jar with boat designs, painted pottery from Egypt, c. 3450–3350 BCE is placed in the Brooklyn Museum, New York3.

Jar with boat designs
Jar with boat designs4

Now if we think for even older evidence, we can look at the island, stand to reason if humans made it to the island, we could sail there. We have the oldest evidence of sea travel by homo-sapiens to any island is Australia. Even at the time of the ice age, Australia was still an island. So how could homo-sapiens reach there?

The Mystics of Physics

Once in my childhood, I travelled from Alibag to Mumbai by a ferry and since then I was fond of the sea. Even my favourite movie-series is Pirates of the Caribbean. I love the way Captain Jack Sparrow steers and handles his Black Pearl. How does he manage to keep moving his ship in the forward direction if the wind flows in any other direction? Let’s find out some interesting physics of sailing.

Basic parts of a sailboat
Basic parts of a sailboat5

To understand the physics behind sailing, we need to know some of the parts of a sailboat that are shown in the diagram below.

Sailing downwind:

(In the exact direction of the wind also known as dead run) Understanding this one is easy. The wind blows into the sails and pushes them forward. The wind speed is greater than the boat so the sail decelerates the wind. But with sailing in the same direction we cannot go beyond the speed of air in this case even by using a spinnaker.

For understanding you can simply make an experiment; take out your hand from the window of a moving car (with precautions). When you place your hand in the air simply facing your palm perpendicular to the wind direction, you will feel the opposite force exerted by the wind which pushes your palm in the direction of air. A similar force acts in the case of sail. Running in the strong wind always feels easier.

Sailing directly upwind:

(In the exact opposite direction of the wind) Understanding this one is easier than previous because one cannot sail in the direction exactly opposite to the wind (No go zone). What if our destination is exactly in the opposite direction? Then you have to sit there and flap the sail. Boats can sail at around 40° to the wind and, by tacking (alternate lines on either side of the wind direction) they can go wherever they want.

Points of sails
Points of sails6

Continuing with the experiment: You have your hand outside of the window; Now tilt your palm slightly towards 45° to the wind direction. The figure explains how you will feel two different forces. One is drag force and the other is lift force. The wind will be deflected and which will push your hand up as well as back.

Introduction of lift force
Introduction to lift force7

Sailing close to wind direction:

This is actually an interesting part. Lift is generated because of the shape of the sails. To flow along with sails positioned in such a manner (as seen in the figure,) the wind has to change its direction. This is shown by initial velocity vi and final velocity vf. the change of velocity dv is in the direction shown. The acceleration aa of the air is dv/dt, so the force Fa that sails exert on the air is in the same direction. (Newton's first and second laws: F = ma.) The force Fw that the wind exerts on the sails is in the opposite direction7.

There is also a Bernoulli Effect which contributes in a secondary way which generates lift force converted into thrust towards the outer side of the curve due to pressure difference as the pressure exerted by faster moving air is less than air with low velocity.

Velocity and force diagram
Velocity and force diagram7

Now this force is mainly sideways on the boat, and it gets more and more sideways as you get closer to the wind. However, part of the force is forward: the direction we want to go.

Can a boat drift sideways? Yes but very little. Because when it does, the Keel, which is a major flat part of the boat is below water, has to push water sideways. The role of the keel is to ensure the stability of the ship. The force exerted on the hull and keel is resisted by the water in the opposite direction. As to the forwards component: it accelerates the boat until the drag force Fd holding it back is big enough so that


Boat heel: (Tilting of the boat) the diagram below shows that the horizontal forces are equal and in the opposite direction but acting at points having a certain distance which generates torque tending the boat to rotate clockwise. This torque is cancelled by another torque generated due to another pair of forces which are buoyancy force and the weight. They are also equal and opposite. As the boat tries to heel, weight is shifted towards the left direction from the central line and buoyancy force on right generates torque which tends the boat to rotate anticlockwise and balance the other torque.7

Boat heel
Boat heel7

Take a break on this line and ask yourself a question -

Up to what maximum speed can a boat reach?

If your answer is “Not more than the speed of the wind”, then you are possibly wrong. An Iceboat can reach a speed six times that of wind. But HOW? It’s about the apparent wind concept...

Concept of apparent wind
Concept of apparent wind8

Consider a situation where wind speed is zero and you are riding a bike. Though actual wind speed is zero, you still feel the wind in the exact opposite direction and equal to the bike speed. Similarly when the boat is already moving, it faces boat speed wind which in addition with the true wind, produces resulting apparent wind.

E.g. Consider a boat is initially sailing with a boat wind speed of 12km/hr and actual wind speed is 10km/hr. The apparent wind speed will be 20km/hr, faster relative to actual wind.

Relative speed
Relative speed

As boat speed increases, apparent wind speed increases and as apparent wind increases, the more force is exerted on sails. Now the greater force is dragging the boat forward. So the boat keeps accelerating until the resistance from the water balances the forward component of sail force.

Now your turn

Imagine a world without sailing. Apart from the colonisation; trade and travel were out of the question. Once upon a time, someone stood on the shores and looked at the vast ocean and thought, “what is it like on the other end?” This sort of curiosity is what drives a human mind and has led our civilization to what it is today. So keep looking out and be curious. And to learn more about such things, consider subscribing to the blog, or following on the social media links below. Thanks!

Next week in Invisible history

Last week's clue was rather a simple one as I received eight correct answers. The first one being from the author of this article. The people who gave the right answers were: sidsingh9669 (Reddit,) samarth1616 (discord,) bashbashheader (Reddit,) Neha Rajput (WhatsApp,) Ali (WhatsApp,) vintageman (Reddit,) and drcoco (discord.)

Last week's clue referred to the series of articles published by the New York Sun. The articles are collectively known as "The Great Moon Hoax." The papers were said to be reprinted from the Edinburgh Journal of Science. The New York Sun, founded in 1833, was one of the new "penny press" papers that appealed to a broader audience with a lower price and a more narrative style of journalism. From the day the first moon hoax article was released, sales of the paper raked up considerably. It was exciting stuff, and readers liked it. The only problem was that none of it was true.

A lithograph of the hoax
A lithograph of the hoax's "ruby amphitheatre", as printed in The Sun.

The clue for next week is something related to History and dates. The clue is "Tomorrow is eleven days after." This is a super exciting subject, and I highly recommend you to think about this. You can write the answers to me in the comment section or on social media. I have left the links down below. If you give the right answer, your name will be mentioned in the next week’s article.

About the author

This article is written by Nikhil Chandratre. Nikhil is a longtime friend of mine and also has answered most of the “This week in invisible history” questions. He is a fellow mechanical engineer and is currently pursuing his master at “Bbw Hochschule, Berlin.” You can follow him on his social media (links below.) If you also want to write about something that you like and are fascinated about, do let me know. New articles every Saturday.

See you next weekend!

  1. Reddit:r/theinvisiblegenius
  2. Instagram: @theinvisiblegenius @berlinkar_nikhil
  3. Twitter: @notnitinchopra

Reference links

  1. Christopher Columbus Ships: Vessels that Discovered America
  2. Vasco da Gama | Biography, Achievements, & Facts | Britannica
  3. Ship - History of ships | Britannica
  4. Photograph by Katie Chao. Brooklyn Museum, New York, Charles Edwin Wilbour Fund, 09.889.400
  5. Image source:
  6. Do you know your points of sail? | Inbrief | e-newsletters | News & Events | RYA - Royal Yachting Association
  7. The Physics of sailing by science@unsw, The University of New South Wales, Sydney.
  8. Apparent wind - Sail better!


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