Winds that blow west in the South Pacific. That is why our route was designed so that on a sailing yacht "Juliet" move from east to west, that is, so that the wind blows in the back.
However, if you look at our route, you will notice that often, for example, when moving from south to north from Samoa to Tokelau, we had to move perpendicular to the wind. And sometimes the direction of the wind changed altogether and had to go against the wind.
Juliet Route
What to do in this case?
Sailing ships have long been able to sail against the wind. Classic Yakov Perelman wrote about this for a long time and simply in his Second book from the series “Entertaining Physics”. This piece I bring here literally with pictures.
"Under sail against the wind
It is difficult to imagine how sailing ships can go “against the wind” - or, in the words of the sailors, go “to a badewind”. True, the sailor will tell you that it is impossible to sail under the wind, but you can only move at an acute angle to the direction of the wind. But this angle is small - about a quarter of the right angle - and it seems, perhaps, equally incomprehensible: whether to swim directly against the wind or at an angle to it of 22 °.
In fact, however, this is not indifferent, and we will now explain how it is possible to go towards it at a slight angle by the force of the wind. First, consider how the wind generally acts on the sail, i.e. where it pushes the sail when it blows on it. You probably think that the wind always pushes the sail in the direction where it is blowing. But this is not so: wherever the wind blows, it pushes the sail perpendicular to the plane of the sail. Indeed: let the wind blow in the direction indicated by the arrows in the figure below; line AB stands for sail.
The wind always pushes the sail at right angles to its plane.
Since the wind presses evenly on the entire surface of the sail, we replace the wind pressure by the force R applied to the middle of the sail. We decompose this force into two: the force Q perpendicular to the sail, and the force P directed along it (see the figure above, to the right). The last force is pushing the sail nowhere, since the friction of the wind on the canvas is insignificant. There remains the force Q, which pushes the sail at right angles to it.
Knowing this, we can easily understand how a sailing ship can go at an acute angle towards the wind. Let the QC line depict the keel line of the vessel.
How can one sail against the wind.
The wind is blowing at an acute angle to this line in the direction indicated by the row of arrows. Line AB depicts a sail; it is placed so that its plane bisects the angle between the direction of the keel and the direction of the wind. Observe the decomposition of forces in the figure. We depict the pressure of the wind on the sail by the force Q, which, as we know, should be perpendicular to the sail. We decompose this force into two: force R, perpendicular to the keel, and force S, directed forward along the keel line of the vessel. Since the movement of the vessel in the direction R encounters strong water resistance (the keel in sailing vessels is very deep), the force R is almost completely balanced by the water resistance. All that remains is force S, which, as you see, is directed forward and, therefore, moves the ship at an angle, as if to meet the wind. [It can be proved that the force S gets its greatest value when the plane of the sail halves the angle between the directions of the keel and wind.]. Usually this movement is performed in zigzags, as the figure below shows. In the language of seafarers, such a movement of the ship is called "tacking" in the strict sense of the word. "
Let's now consider all the possible wind directions relative to the course of the boat.
Scheme of the ship's courses relative to the wind, that is, the angle between the direction of the wind and the vector from the stern to the bow (heading). 
When the wind blows in the face (leventik), the sails dangle from side to side and it is impossible to move with the sail. Of course, you can always lower the sails and turn on the motor, but this is no longer related to sailing.
When the wind blows right in the back (forwind, tailwind), dispersed air molecules exert pressure on the sail from one side and the boat moves. In this case, the ship can only move slower than the wind speed. Here the analogy of riding a bicycle in the wind works - the wind blows in the back and pedaling is easier.
When moving against the wind (badewind), the sail does not move due to the pressure of air molecules on the sail from behind, as in the case of a fordewind, but because of the lifting force, which is created due to different air speeds from two sides along the sail. At the same time, due to the keel, the boat does not move in a direction perpendicular to the boat heading, but only forward. That is, the sail in this case is not an umbrella, as in the case of a badewind, but an airplane wing.
During our crossings, we mainly walked with buckstacks and half-horses with an average speed of 7-8 knots with a wind speed of 15 knots. Sometimes we walked upwind with a gulfwind and a badewind. And when the wind died out, they turned on the motor.
In general, a boat with a sail going against the wind is not a miracle, but a reality.
The most interesting thing is that boats can walk not only against the wind, but even faster than the wind. This happens when the boat goes backstage, creating its own wind.
Tacks, Complete courses, Tacking, Pennant wind and ...
Tack - the direction of movement relative to the wind, when the angle formed with the direction of the wind is greater than zero.
Accordingly, the right tack is the right foot or arm in front, that is, you always stand with your back to the wind, and the movement to the right side is the right tack, to the left side is the left tack. Depending on the magnitude of this angle, the course relative to the wind line can be sharp or complete.
- Leventik (le vent)- the position of the vessel relative to the wind when the angle to the wind line is near zero. Since the sailing ship cannot go on such a course, they usually do not say “course”, but “leventik position”.
- Badewind (bij de wind)- a sharp course relative to the wind line when the wind blows at an angle from 0 to 80 °. It can be steep badewind (up to 50 °) and full (from 50 to 80 °).
Full coursesconsidered when the wind blows at an angle close to 90 ° or at an obtuse angle to the direction of travel. These courses include:
- Gulfwind (halve wind), or half-wind - the wind blows at an angle from 80 ° to 100 °.
- Bakstag- the wind blows at an angle from 100 to 150 ° (steep backstroke) and from 150 ° to 170 ° (full backstop).
- Fordewind - the very “tailwind” that sailors desire, although in sailing this course is by no means the fastest, as one would expect. The wind blows into the stern at an angle from 170 ° of one side to 170 ° of the other side.
Tack.
You cannot go directly against the wind. If you need to get to any point located upstream, then tacking is applied, movement to the target with a badewind course - with variable tacks. To change the tack you need to make a turn. Also remember that with any course you drift (merge) a little in the wind, therefore you cannot clearly set the direction of movement to a point, you should always take a course a little higher in the wind, that is, with a margin.
Determining wind directions relative to you.
- Windward side - when you stand with your back to the wind, the back will be the windward side, respectively - the windward side of the board where the heels are.
- Leeward side - on the contrary, this is all that is in front of you (downwind) when you stand with your back to the wind. The leeward side is where your socks are on the board.
Pennant wind (Apparent Wind).
Pennant wind speed is the geometric sum of the true wind speed and the wind caused by the movement of the yacht (heading wind). If the speed of movement on water is 1 m / s, then the speed of the induced wind is 1 m / s in the direction of the bow. The faster the athlete moves, the stronger the induced wind, and - accordingly, the stronger the pennant wind. It also intensifies if you go in the true wind (against the wind).
I think that many of us would take the chance to plunge into the sea abyss on some kind of underwater vehicle, but still, most would prefer a sea trip on a sailboat. When there were no planes or trains, there were only sailboats. Without them, the world was, did not become so.
Sailboats with direct sails brought Europeans to America. Their stable decks and roomy holds delivered people and supplies for the construction of the New World. But these old ships also had their limitations. They walked slowly and almost in the same direction in the wind. Since then, much has changed. Today, completely different principles of controlling the strength of wind and waves are used. So if you want to ride in modern, you have to learn physics.
Modern sailing is not just the movement in the wind, it is something affecting the sail, and forcing it to fly like a wing. And this invisible “something” is called the lifting force, which scientists call the lateral force.
An attentive observer could not fail to notice that no matter where the wind blows, the sailing yacht always moves to where the captain needs - even when the wind is opposite. What is the secret to such an amazing combination of stubbornness and obedience.
Many do not even realize that a sail is a wing, and the principle of operation of a wing and a sail is one. It is based on the lifting force, only if the lifting force of the wing of the aircraft, using the headwind, pushes the plane up, then the vertically located sail directs the sailboat forward. To explain this scientifically, you need to return to the roots - how the sail works.
Look at the simulated process, which shows how air acts on the plane of the sail. Here you can see that the air flows under the model, having a greater bend, bend to bypass it. At the same time, the stream has to accelerate a little. As a result, an area of \u200b\u200blow pressure arises - this generates lift. Low pressure on the lower side pulls the sail to the bottom.
In other words, the high-pressure area is trying to move to the low-pressure area, putting pressure on the sail. There is a pressure difference that generates lift. Due to the shape of the sail, on the windward side, the wind speed is lower than on the windward side. On the outside, a vacuum forms. The sail is literally sucked in air, which pushes the sailing yacht forward.
In fact, this principle is quite simple to understand, just look at any sailing vessel. The trick here is that no matter how the sail is located, it transfers wind power to the ship and even if it visually seems that the sail should slow the yacht, the center of application of forces is closer to the bow of the sailboat, and the wind force provides forward movement.
But this is a theory, but in practice, everything is a little different. In fact, a sailing yacht cannot go against the wind - it moves at a certain angle to it, the so-called tacks.
The sailboat moves due to the balance of forces. Sails act like wings. Most of their lifting force is directed to the side, and only a small amount forward. However, the secret is in this wonderful phenomenon in the so-called "invisible" sail, which is located under the bottom of the yacht. This keel or in the marine language is a daggerboard. The lifting force of the dagger also produces lifting force, which is also directed mainly to the side. The keel resists roll and the opposite force acting on the sail.
In addition to the lifting force, a roll also arises - a phenomenon harmful to forward movement and dangerous to the ship's crew. But for that, there is a team on the yacht to serve as a living counterweight to the inexorable physical laws.
In a modern sailboat, both the keel and the sail together direct the sailboat forward. But as any beginner sailor confirms in practice, everything is much more complicated than in theory. An experienced sailor knows that the slightest changes in the bend of the sail make it possible to get more lift and control its direction. By changing the bend of the sail, a skilled sailor controls the size and location of the area producing lift. Using a deep forward bend, you can create a large pressure zone, but if the bend is too large or the leading edge is too steep air molecules, the flowing around will cease to follow its bend. In other words, if the subject has sharp corners of the particle’s flow, they will not be able to make a turn — the momentum of movement is too strong, this phenomenon is called “separated flow”. The result of this effect is that the sail “rinses”, losing the wind.
Here are some more practical tips for using wind power. The optimal course of going into the wind (racing blade). The sailors call it "the move against the wind." Pennant wind, having a speed of 17 knots, is significantly faster than the true wind that creates the wave system. The difference in their directions is 12 °. The course to the pennant wind is 33 °, to the true wind - 45 °.
It is difficult to imagine how sailing ships can go “against the wind” - or, in the words of the sailors, go “to a badewind”. True, the sailor will tell you that it is impossible to sail under the wind, but you can only move at an acute angle to the direction of the wind. But this angle is small - about a quarter of the right angle - and it seems, perhaps, equally incomprehensible: whether to swim directly against the wind or at an angle to it of 22 °.
In fact, however, this is not indifferent, and we will now explain how it is possible to go towards it at a slight angle by the force of the wind. First, consider how the wind generally acts on the sail, i.e. where it pushes the sail when it blows on it. You probably think that the wind always pushes the sail in the direction where it is blowing. But this is not so: wherever the wind blows, it pushes the sail perpendicular to the plane of the sail. Indeed: let the wind blow in the direction indicated by the arrows in the figure below; line AB denotes a sail.
The wind always pushes the sail at right angles to its plane.
Since the wind presses evenly on the entire surface of the sail, we replace the wind pressure by the force R applied to the middle of the sail. We decompose this force into two: force Qperpendicular to the sail, and the force P directed along it (see. Fig. above, right). The last force is pushing the sail nowhere, since the friction of the wind on the canvas is insignificant. Power remains Qwhich pushes the sail at right angles to it.
Knowing this, we can easily understand how a sailing ship can go at an acute angle towards the wind. Let the line QC depicts the keel line of the vessel.
How can one sail against the wind.
The wind is blowing at an acute angle to this line in the direction indicated by the row of arrows. Line AB depicts a sail; it is placed so that its plane bisects the angle between the direction of the keel and the direction of the wind. Observe the decomposition of forces in the figure. The pressure of the wind on the sail we depict by force Q, which, we know, should be perpendicular to the sail. We decompose this force into two: force Rperpendicular to the keel and force Sdirected forward along the keel line of the vessel. Since the movement of the ship in the direction R encounters strong water resistance (keel in sailing vessels becomes very deep), then the force R almost completely balanced by water resistance. Only power remains S, which, as you see, is directed forward and, therefore, moves the ship at an angle, as if to meet the wind. [It can be proved that strength S gets the greatest value when the sail plane bisects the angle between the keel and wind directions.].Usually this movement is performed in zigzags, as the figure below shows. In the language of sailors, such a movement of the ship is called "tacking" in the strict sense of the word.
It is difficult to imagine how sailing ships can go “against the wind” - or, in the words of the sailors, go “to a badewind”. True, the sailor will tell you that you can’t go sailing directly against the wind, but you can only move at an acute angle to the direction of the wind 3. But this angle is small - about a quarter of the right angle - and it seems, perhaps, equally incomprehensible: whether to swim directly against the wind or at an angle to it of 22 °.
3 (You can use only wind energy and move strictly against the wind if you replace the sail with a wind turbine such as a windmill, which will rotate the ship’s propeller. There is even the well-known task of P. L. Kapitsa about such an unusual vessel at first glance (see also the journal: Boats and Yachts, 1981, No. 1, p. 25).)
In fact, however, this is not indifferent, and we will now explain how it is possible to go towards it at a slight angle by the force of the wind. First, consider how the wind generally acts on the sail, i.e. where it pushes the sail when it blows on it. You probably think that the wind always pushes the sail in the direction where it is blowing. But this is not so: wherever the wind blows, it pushes the sail perpendicular to the plane of the sail.
Indeed. Let the wind blow in the direction indicated by the arrows in fig. 17, line AB depicts a sail.
Since the wind presses evenly on the entire surface of the sail, we replace the force of the wind pressure by the force Rattached to the middle of the sail. We decompose this force into two: force Qperpendicular to the sail and strength R directed along it forward. Force R the sail is not pushing anywhere, since the friction of the wind on the canvas is insignificant. Power remains Qwhich pushes the sail at right angles to it.
Knowing this, we can easily understand how a sailing ship can go at an acute angle towards the wind. Let the QC line (Fig. 18) depict the keel line of the vessel. The wind is blowing at an acute angle to this line in the direction indicated by the arrows. Line AB depicts a sail; it is placed so that its plane bisects the angle between the direction of the keel and the direction of the wind. Follow in fig. 18. for the decomposition of forces. We depict the pressure of the wind on the sail by the force Q, which, as we know, should be perpendicular to the sail. We decompose this force into two: force B, perpendicular to the keel, and force S, directed forward along the keel line of the vessel. Since the movement of the vessel in the direction B meets strong water resistance (the keel in sailing vessels is very deep), the force B is almost completely balanced by the water resistance. All that remains is force S, which, as you see, is directed forward and, therefore, moves the ship at an angle, as if to meet the wind *. Usually this movement is performed in zigzags, as shown in Fig. 19. In the language of seafarers, such a movement of a ship is called “tacking” in the full sense of the word 4.
* (It can be proved that the force S gets the greatest value when the plane of the sail halves the angle between the directions of the keel and wind.)
4 (There are a number of issues in sailing that are interesting from the point of view of a physicist. More information about this sport and some technical problems of sailing can be found, for example, from the books: Glovatsky V. The fascinating world of sails: Essays on the history of sailing.- M .: Progress, 1979; Proctor I. Sailing. Wind, wave and current .-- L .: Gidrometeoizdat, 1981.)