It is hard to imagine how sailing ships can go "against the wind" - or, in the words of the sailors, go "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 of 22 ° to it.
3 (You can use only wind energy and move strictly against the wind if you replace the sail with a wind turbine of the type windmill, which will rotate the ship's propeller. There is even a well-known problem of P. L. Kapitsa about such an unusual at first glance vessel (see also the magazine: Katera i Yachts, 1981, No. 1, p. 25).)
In fact, 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. Let us first consider how the wind acts on the sail in general, 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 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 represents a sail.
Since the wind pushes evenly over the entire surface of the sail, we replace the wind pressure force with the force R applied to the middle of the sail. Let's decompose this force into two: the force Q, perpendicular to the sail, and the force R directed forward along it. Force R does not push the sail anywhere, since the friction of the wind on the canvas is negligible. The power remains 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 into the wind. Let the KK line (Fig. 18) represent the keel line of the vessel. The wind blows at an acute angle to this line in the direction indicated by the arrows. The line AB represents the 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 breakdown of forces. We represent the pressure of the wind on the sail by the force Q, which, 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 direction B encounters strong water resistance (the keel in sailing ships is very deep), the force B is almost completely balanced by water resistance. There remains only the 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 vessel is called "tacking" in the full sense of the word 4 .
* (It can be shown that the force S is greatest when the plane of the sail bisects the angle between the directions of the keel and the wind.)
4 (There are a number of issues in sailing that are interesting from a physicist's point of view. More about this sport and some technical problems sailing can be learned, for example, from the books: Glovatsky V. The fascinating world of sails: Essays on the history of sailing. - M .: Progress, 1979; Proctor Ya. Sailing. Wind, excitement and flow. - L .: Gidrometeoizdat, 1981.)
Vessel's course relative to the wind - the angle between the direction of the wind and the diametrical plane of the vessel, that is, the heading angle to the horizon point from which the wind blows, expressed in angular degrees or rhumbs.
Depending on the value of this angle, the courses relative to the wind have their own names:
1 - close-hauled (30° - 45°);
2 - full haul (45° - 75°);
3 - gulfwind (about 90 °);
4 - backstay (110° - 160°);
5 - jibe (160°-200°);
6 - leventik (30 ° on each side)
Leventik (fr. le vent) - a course that forms an angle close to 180 degrees with the direction of the wind, that is, the wind blows almost exactly in front of the ship. Since a sailing ship cannot go in such a course, they usually say not “course”, but “headward position”.
Beidewind (Dutch. bij de wind) - a course at which the angle between the direction of the wind and the direction of the vessel's movement is more than 100 degrees (less than 8 points). Allocate a close-hauled full (from 100 to 120 degrees) and steep (more than 120 degrees). The thrust of the sail is entirely determined by its lifting force, with an increase in frontal resistance, the thrust force decreases, but the drift force increases. Thus, on this course, the sail, set with a minimum angle of attack to the apparent wind (5-10 °), works as an aerodynamic wing.
The best sailboats sail at an angle of 30-35° to the direction true wind. Due to the addition of the wind speed vectors and the oncoming air flow, the speed of the pennant wind on the hauled course is maximum, as well as the aerodynamic force on the sail, which is proportional to the square of the wind speed. The drift force also reaches its maximum value. If you try to go at a sharper angle to the wind, then the speed of the vessel will decrease, the sail will begin to rinse, the aerodynamic force will decrease and, finally, there will come a moment when the drag of the sail and the resistance of the water to the movement of the boat will greatly exceed the thrust. The ship will reverse.
Gulfwind (Dutch. halve wind), or half a wind - a course at which the angle between the direction of the wind and the direction of the vessel's movement is approx. 8 points (from 80 to 100 degrees). On this course, the wind blows perpendicular to the DP, and the apparent wind is directed from the bow at an acute angle to the DP. Accordingly, the sail is set at a lower angle of attack, its thrust is equal to the lifting force, and the drift force is equal to the drag of the sail. on this course, the sail should bisect the angle between the DP and the direction of the apparent wind approximately in half.
Backstay (Dutch. bakstag) - a course that forms an angle with the direction of the wind greater than 8, but less than 16 rhumbs (more than ten and less than eighty degrees), that is, the wind blows from behind to the side of the ship; they distinguish the full backstay course, at which the angle is no more than twenty degrees, that is, approaching the jib; the sail is set at an angle to the wind from the lee side. Usually on this course the sailing vessel develops the highest speed. On the backstay, the sail operates at a high angle of attack, where drag plays a major role in generating sail thrust. The drift force is practically non-existent.
Vordewind (Dutch. voor de wind) - the course at which the wind is directed to the stern of the ship.
The jibe is the same "fair wind" that sailors wish for, although in sailing this course is by no means the fastest, as one would expect. In addition, it requires attention and skill from the helmsman to manage additional sails (usually a spinnaker). In this case, the sail is placed perpendicular to the direction of the wind, the thrust on it is created due to drag. A weak wind on this course is practically not felt, since the speed of the apparent wind is equal to the difference between the speed of the true wind and the speed of the oncoming air flow.
A jibe is one of two turns (turn - change of tack) of a sailing vessel, in which the direction of the wind at the time of the turn passes through the stern. Unlike the tack, the jibe is more complex and, at times, dangerous, requiring clear team actions when working with sails. It is no coincidence that the command is given with the clarification: “Prepare to jibe!”, While when turning the “tack”, the commander simply commands “Prepare to turn!”.
Lavrovka
Laying a sailing ship. α - tacking angle
A sailboat cannot sail directly into the wind. If it is necessary to get to any point located from the windward, then tacking is used - movement towards the target in a close-hauled course with variable tacks. To change tack, you must make a turn.
If, while keeping the tack, you need to go at a sharper angle to the direction of the wind, then they say that you need to "be brought to the wind." If, on the contrary, it is necessary to increase the angle between the direction of the wind and the DP of the boat, then they say that it is necessary to “fall off into the wind”. (It should, however, be remembered that “the wind blows into the compass”, that is, its directions are given not according to where the wind is blowing, but from where. This means that if the ship’s heading is, for example, north and the wind is from north, it does not blow along the way, but towards the ship.)
In order to set the sail at the optimal angle of attack during these maneuvers, it must be pulled up to the DP - “select”, or released - “poison”. Yachtsmen use these terms for all manipulations with tackle - sheets, braces, etc.
Depending on the side from which the wind is blowing, the courses relative to the wind can be starboard and port tack.
With a heading wind angle of 26 points, the right tack hauled in the sailing fleet was sometimes called a starboard, and the left tack (wind heading angle of 6 points) was called a backboard. To clarify the course relative to the wind, the expressions were used: “the ship is sailing on the starboard tack 7 points to the wind” (that is, hauled at a heading wind angle of 78 °); “The ship is backstay on the starboard tack 10 points” (that is, the heading angle of the wind is 112 °); “The ship sails a starboard fuller than 6 points” (that is, a backstay at a heading angle of 12 points, or 135 °). The concept of "close-hauled" is also used, as the sharpest course relative to the wind, in which a sailing vessel can go forward (it ranges from 3 to 6 points 33.3 / 4 ° to 67.1 / 2 °); steep and full backstay (up to 12 points and more than 12 rubles, or up to 135 ° and more than 135 °, respectively).
Calculate the ship's path from known compass values. wind direction, heading over wind, compass and nas drift corrections. in the sailing fleet by correcting points.
| Rumba | degrees | Vessel's course relative to the wind |
| 0 | 0 | Leventik |
| 1 | 11,25 | Close-hauled, port tack |
| 2 | 22,5 | Close-hauled, port tack |
| 3 | 33,75 | Close-hauled, port tack |
| 4 | 45 | Close-hauled, port tack |
| 5 | 56,25 | Full haul, port tack |
| 6 | 67,5 | Full haul, port tack |
| 7 | 78,75 | Full haul, port tack |
| 8 | 90 | Gulfwind, port tack |
| 9 | 101,25 | Gulfwind, port tack |
| 10 | 112,5 | Backstay, left tack |
| 11 | 123,75 | Backstay, left tack |
| 12 | 135 | Backstay, left tack |
| 13 | 146,25 | Backstay, left tack |
| 14 | 157,5 | Backstay, left tack |
| 15 | 168,75 | Backstay, left tack |
| 16 | 180 | jibe |
| 17 | 191,25 | Backstay, starboard tack |
| 18 | 202,5 | Backstay, starboard tack |
| 19 | 213,75 | Backstay, starboard tack |
| 20 | 225 | Backstay, starboard tack |
| 21 | 236,25 | Backstay, starboard tack |
| 22 | 247,5 | Backstay, starboard tack |
| 23 | 258,75 | Gulfwind, starboard tack |
| 24 | 270 | Gulfwind, starboard tack |
| 25 | 281,25 | |
| 26 | 292,5 | Full haul, starboard tack |
| 27 | 303,75 | Full haul, starboard tack |
| 28 | 315 | |
| 29 | 326,25 | Close-hauled, starboard tack |
| 30 | 337,5 | Close-hauled, starboard tack |
| 31 | 348,75 | Close-hauled, starboard tack |
| 32 | 360 | Leventik |
The movement of a sailing yacht downwind is actually determined by the simple pressure of the wind on her sail, pushing the vessel forward. However, as wind tunnel research has shown, sailing upwind exposes the sail to a more complex set of forces.
When ram air flows around the concave rear surface of the sail, the air speed decreases, while when flowing around the convex front surface of the sail, this speed increases. As a result, a region of increased pressure is formed on the back surface of the sail, and a region of reduced pressure is formed on the front surface. The pressure difference on the two sides of the sail creates a pulling (pushing) force that moves the yacht forward at an angle to the wind.
A sailing yacht, located approximately at right angles to the wind (in nautical terminology, a yacht is on a tack), moves quickly forward. The sail is subjected to pulling and lateral forces. If sailing yacht goes at an acute angle to the wind, its speed slows down due to a decrease in the pulling force and an increase in the lateral one. The more the sail is turned aft, the slower the yacht moves forward, in particular due to the large lateral force.
A sailboat cannot sail directly into the wind, but it can move forward by making a series of short, zigzag movements at an angle to the wind called tacks. If the wind blows to the port side (1), they say that the yacht is on the left tack, if to starboard (2) - the starboard tack. In order to cover the distance faster, the yachtsman tries to increase the speed of the yacht to the limit by adjusting the position of her sail, as shown in the figure below to the left. To minimize deviation from a straight line, the boat moves by changing course from starboard to port tack and vice versa. When the yacht changes course, the sail is thrown to the other side, and when its plane coincides with the wind line, it rinses for some time, i.e. is inactive (middle figure below the text). The yacht enters the so-called dead zone, losing speed until the wind blows the sail again from the opposite side.
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 exactly as long as we do not think about them. For example, you can find out how spaceships do not miss or collide with the ISS during docking.
1. Strictly against the wind sailing is impossible. However, if the wind is blowing in front, but slightly at an angle, the yacht may well move. In such cases, the ship is said to be on a sharp course.
2. The thrust of the sail is formed due to two factors. Firstly, the wind simply presses on the sails. Secondly, slanting sails, installed on most modern yachts, when flowing around with air, work like an airplane wing and create “lift”, only it is not directed upwards, but forward. Due to aerodynamics, the air moves faster on the convex side of the sail than on the concave side, and the pressure on the outside of the sail is less than on the inside.
3. The total force generated by the sail is directed perpendicular to the canvas. According to the vector addition rule, it is possible to distinguish the drift force (red arrow) and the thrust force (green arrow) in it.
4. On sharp courses, the drift force is great, but it is opposed by the shape of the hull, keel and rudder: the yacht cannot go sideways due to water resistance. But forward it willingly slides even with a small traction force.
5. To go strictly against the wind, the yacht tacks: it turns to the wind with one or the other side, moving forward in segments - tacks. How long should the tacks be and at what angle to the wind to go － important questions of skipper tactics.
6. There are five main courses of the vessel relative to the wind. Thanks to Peter I, Dutch maritime terminology took root in Russia.
7. Leventik－ the wind is blowing directly into the bow of the ship. You can’t sail on such a course, but a turn to the wind is used to stop the yacht.
8. Tailwind－ the same sharp course. When you are 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 is blowing perpendicular to the direction of travel.
10. Backstay－ the wind blows from the stern and from the side. This is the fastest course. Fast backstay racing boats are able to accelerate to speeds greater than wind speed due to the lift of the sail.
11. Giving－ the same tailwind blowing from the stern. Contrary to expectations, not the fastest course: here the lift 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 that an airplane pilot can predict updrafts and downdrafts.
You can view an interactive version of the diagram on the "Two Minutes Explained" blog.
“Fair wind!” - wish all sailors, and completely in vain: when the wind blows from the stern, the yacht is not able to develop maximum speed. I helped make this diagram. Vadim Zhdan, professional skipper, racer, organizer and host of yacht regattas. Read the tooltips on the diagram to find out.
2. The thrust of the sail is due to two factors. Firstly, the wind simply presses on the sails. Secondly, slanting sails, installed on most modern yachts, work like an airplane wing when flowing around with air, and only it is not directed upwards, but forward. Due to aerodynamics, the air moves faster on the convex side of the sail than on the concave side, and the pressure on the outside of the sail is less than on the inside.
3. The full force generated by the sail is directed perpendicular to the canvas. According to the vector addition rule, it is possible to distinguish the drift force (red arrow) and the thrust force (green arrow) in it.
5. To go strictly against the wind, the yacht tacks: turns to the wind with one or the other side, moving forward in segments - tacks. How long should the tacks be and at what angle to the wind to go － important questions of skipper tactics.
9. gulfwind－ the wind is blowing perpendicular to the direction of travel.
11. jibe－ the same tailwind blowing from the stern. Contrary to expectations, not the fastest course: here the lift 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
