How sailing ships can move against the wind. Yachting Lessons: Why can a yacht sail against the wind? True and apparent winds in yachting

It is difficult to imagine how sailing ships can go “against the wind” - or, as sailors say, go “close-hauled”. True, a sailor will tell you that you cannot sail 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 a right angle - and it seems, perhaps, equally incomprehensible: whether to sail directly against the wind or at an angle to it of 22°.

3 (It is possible to use only wind energy and move strictly against the wind if the sail is replaced with a wind engine like windmill, which will rotate the ship's propeller. There is even a well-known problem by P. L. Kapitsa about such an unusual vessel at first glance (see also the magazine: Boats and Yachts, 1981, No. 1, p. 25).)

In reality, however, this is not indifferent, and we will now explain how it is possible to move towards it at a slight angle by the force of the wind. First, let's look at how the wind generally acts on the sail, that is, where it pushes the sail when it blows on it. You probably think that the wind always pushes the sail in the direction it blows. 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 wind pressure with force R, applied to the middle of the sail. Let's break this force down into two: force Q, perpendicular to the sail, and the force R directed forward along it. Force R the sail does not push anywhere, since the friction of the wind on the canvas is negligible. Strength remains Q, which pushes the sail at right angles to it.

Knowing this, we can easily understand how a sailing ship can sail at an acute angle towards the wind. Let line KK (Fig. 18) represent the keel line of the ship. The wind blows at an acute angle to this line in the direction indicated by the arrows. Line AB represents a sail; it is placed so that its plane bisects the angle between the direction of the keel and the direction of the wind. Trace in Fig. 18. for the disintegration of forces. We represent the wind pressure on the sail by force Q, which, we know, must be perpendicular to the sail. Let us divide 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 direction B encounters strong resistance from the water (keel in sailing ships becomes very deep), then the force B is almost completely balanced by the resistance of the water. There remains only one force S, which, as you see, is directed forward and, therefore, moves the ship at an angle, as if towards the wind *. Usually this movement is performed in zigzags, as shown in Fig. 19. In the language of sailors, such a movement of the ship is called “tacking” in the full sense of the word 4.

* (It can be proven that the force S is greatest when the plane of the sail bisects the angle between the keel and wind directions.)

4 (There are a number of issues in sailing that are interesting from a physicist's point of view. You can learn more about this sport and some of the technical problems of sailing, for example, from the books: Glovatsky V. Fascinating world sails: Essays on the history of sailing. - M.: Progress, 1979; Proctor Ya. Sailing. Wind, waves and currents. - L.: Gidrometeoizdat, 1981.)

We continue the series of publications prepared by the interactive popular science blog “I’ll Explain in Two Minutes.” The blog talks about simple and complex things that surround us every day and do not raise any questions until we think about them. For example, there you can find out how spaceships do not miss and do not collide with the ISS when docking.

1. It is impossible to sail strictly against the wind. However, if the wind is blowing from the front, but slightly at an angle, the yacht may well move. In such cases, the ship is said to be sailing on a sharp course.

2. The thrust of a sail is generated by two factors. Firstly, the wind simply presses on the sails. Secondly, the oblique sails installed on most modern yachts, when air flows around them, work like an airplane wing and create a “lifting force”, only it is directed not upward, but forward. Due to the peculiarities of aerodynamics, the air from the convex side of the sail moves faster than from the concave side, and the pressure from outside There are fewer sails than with the inner one.

3. The total force created by the sail is directed perpendicular to the canvas. According to the rule of vector addition, it is possible to distinguish the drift force (red arrow) and the traction force (green arrow).

4. On sharp courses, the drift force is great, but it is countered by the shape of the hull, keel and rudder: the yacht cannot go sideways due to water resistance. But it willingly slides forward even with a small traction force.

5. To sail strictly against the wind, the yacht tacks: it turns to the wind first on one side or the other, moving forward in segments - tacks. How long the tacks should be and at what angle to the wind should be － important issues of skipper tactics.

6. There are five main courses of a ship relative to the wind. Thanks to Peter I, Dutch maritime terminology took root in Russia.

7. Leventik－ the wind blows directly at the bow of the ship. It is impossible to sail this way, but turning to the wind is used to stop the yacht.

8. Closed wind－ the same acute course. When you go close-hauled, the wind blows in your face, so it seems that the yacht is developing a very high speed. In fact, this feeling is deceptive.

9. Gulfwind－ the wind blows perpendicular to the direction of movement.

10. Backstay－ the wind blows from the stern and from the side. This is the fastest course. Fast racing boats sailing backstayed can accelerate to speeds exceeding the speed of the wind due to the lifting force of the sail.

11. Fordewind－ the same tailwind blowing from the stern. Contrary to expectations, it is not the fastest course: here the lifting power of the sail is not used, and the theoretical speed limit does not exceed the speed of the wind. An experienced skipper can predict invisible air currents just like an airplane pilot can predict updrafts and downdrafts.

You can view an interactive version of the diagram on the “I’ll Explain in Two Minutes” blog.

It is difficult to imagine how sailing ships can go “against the wind” - or, as sailors say, go “close-hauled”. True, a sailor will tell you that you cannot sail directly against 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 a right angle - and it seems, perhaps, equally incomprehensible: whether to sail directly against the wind or at an angle to it of 22°.

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 with a force R applied to the middle of the sail. Let's break this force down into two: force Q, perpendicular to the sail, and the force P directed along it (see figure above, right). The last force pushes the sail nowhere, since the friction of the wind on the canvas is insignificant. Strength remains Q, which pushes the sail at right angles to it.

Knowing this, we can easily understand how a sailing ship can sail at an acute angle towards the wind. Let the line QC depicts the keel line of the ship.

How can you sail against the wind?

The wind blows at an acute angle to this line in the direction indicated by a series 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. Follow the distribution of forces in the figure. We represent the force of the wind on the sail Q, which we know should be perpendicular to the sail. Let's break this force down into two: force R, perpendicular to the keel, and the force S, directed forward, along the keel line of the vessel. Since the ship's movement is in the direction R meets strong water resistance (the keel in sailing ships is made very deep), then the force R almost completely balanced by water resistance. Only strength remains S, which, as you can see, is directed forward and, therefore, moves the ship at an angle, as if towards the wind. [It can be proven that the force S receives the greatest value when the plane of the sail bisects the angle between the directions of the keel and the wind.]. Usually this movement is performed in zigzags, as shown in the figure below. In the language of sailors, such a movement of the ship is called “tacking” in the strict sense of the word.

I think that many of us would take the chance to dive into the abyss of the sea on some kind of underwater vehicle, but still, most would prefer cruise on a sailboat. When there were no planes or trains, there were only sailboats. Without them the world was not what it was.

Sailboats with straight sails brought Europeans to America. Their stable decks and capacious holds carried men and supplies to build the New World. But these ancient ships also had their limitations. They walked slowly and almost in the same direction with the wind. A lot has changed since then. Today they use completely different principles for controlling the power of wind and waves. So if you want to ride a modern one, you’ll have to learn some physics.

Modern sailing it's not just moving with the wind, it's something that acts on the sail and makes it fly like a wing. And this invisible “something” is called lift, which scientists call lateral force.

An attentive observer could not help but notice that no matter which way the wind blows, the sailing yacht always moves where the captain wants it - even when the wind is headwind. What is the secret of such an amazing combination of stubbornness and obedience.

Many people don’t even realize that a sail is a wing, and the principle of operation of a wing and a sail is the same. It is based on lift only if the lift of the wing aircraft, using the headwind, pushes the plane upward, then the vertically positioned sail directs the sailboat forward. To explain this from a scientific point of view, it is necessary to go back to the basics - how a sail works.

Look at the simulated process that shows how air acts on the plane of the sail. Here you can see that the air flows under the model, which have a greater bend, bend to go around it. In this case, the flow has to speed up a little. As a result, an area of low pressure appears - this generates lift. The low pressure on the underside pulls the sail down.

In other words, an area of high pressure tries to move toward an area of low pressure, putting pressure on the sail. A pressure difference arises, which generates lift. Due to the shape of the sail, the wind speed on the inside windward side is lower than on the leeward side. A vacuum forms on the outside. Air is literally sucked into the sail, which pushes the sailing yacht forward.

In fact, this principle is quite simple to understand; just look at any sailing ship. The trick here is that the sail, no matter how it is positioned, transfers wind energy to the ship, and even if visually it seems that the sail should slow down the yacht, the center of application of forces is closer to the bow of the sailboat, and the force of the wind provides forward motion.

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.

A sailboat moves due to the balance of forces. The sails act like wings. Most of the lift they produce is directed laterally, with only a small amount forward. However, the secret to this wonderful phenomenon is the so-called “invisible” sail, which is located under the bottom of the yacht. This is a keel or, in nautical language, a centerboard. The lift of the centerboard also produces lift, which is also directed mainly to the side. The keel resists heel and the opposing force acting on the sail.

In addition to the lifting force, a roll also occurs - a phenomenon harmful to forward movement and dangerous for the crew of the ship. But that’s why there is a crew on the yacht, to serve as a living counterweight to the inexorable laws of physics.

In a modern sailboat, both the keel and the sail work together to propel the sailboat forward. But as any novice sailor will confirm, in practice everything is much more complicated than in theory. An experienced sailor knows that the slightest change in the bend of the sail makes it possible to obtain more lift and control its direction. By changing the bend of the sail, a skilled sailor controls the size and location of the area that produces lift. With a deep forward bend you can create large area pressure, but if the bend is too great or the leading edge of the air molecules is too steep, the flow around them will no longer follow the bend. In other words, if the object has sharp corners, the particles of the flow cannot make a turn - the momentum of the movement is too strong, this phenomenon is called “separated flow”. The result of this effect is that the sail will “sweep”, losing the wind.

And here are a few more practical advice use of wind energy. Optimal heading into the wind (racing close-hauled wind). Sailors call it “sailing against the wind.” The apparent wind, which has a speed of 17 knots, is noticeably faster than the true wind that creates the wave system. The difference in their directions is 12°. Course to apparent wind - 33°, to true wind - 45°.

“Tailwind!” - they wish all sailors, and it is completely in vain: when the wind blows from the stern, the yacht is not able to reach maximum speed. Helped me make this diagram Vadim Zhdan, professional skipper, racer, organizer and presenter yacht regattas.Read the tooltips on the diagram to figure it out.

2. The thrust of a sail is generated due to two factors. Firstly, the wind simply presses on the sails. Secondly, the oblique sails installed on most modern yachts, when air flows around them, act like an airplane wing, only it is directed not upward, but forward. Due to aerodynamics, the air on the convex side of the sail moves faster than on the concave side, and the pressure on the outside of the sail is less than on the inside.

5. To sail strictly against the wind, the yacht tacks: it turns to the wind with one side or the other, moving forward in segments - tacks. How long the tacks should be and at what angle to the wind should be － important issues of skipper tactics.

9. Gulfwind－ the wind blows perpendicular to the direction of movement.

11. Fordewind－ the same tailwind blowing from the stern. Contrary to expectations, it is not the fastest course: here the lifting power of the sail is not used, and the theoretical speed limit does not exceed the speed of the wind. An experienced skipper can predict invisible air currents in the same way

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