The course of the yacht relative to the wind (Rumb of sailing). How do sailboats manage to sail against the wind? Wind direction in sailing
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 such as a 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 ship in direction B encounters strong resistance from the water (the keel in sailing ships is very deep), 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: V. Glovatsky. The fascinating world of sails: Essays on the history of sailing. - M.: Progress, 1979; Proctor Ya. Sailing. Wind, waves and currents. - L.: Gidrometeoizdat, 1981.)
The movement of a sailing yacht in the wind is actually determined by the simple pressure of the wind on its sail, pushing the ship forward. However, wind tunnel research has shown that sailing upwind exposes the sail to a more complex set of forces.
When the incoming 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, an area of high pressure is formed on the back surface of the sail, and a low pressure area 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, the yacht is tacked) moves quickly forward. The sail is subject to pulling and lateral forces. If a sailing yacht sails at an acute angle to the wind, its speed slows down due to a decrease in the pulling force and an increase in the side force. The more the sail is turned towards the stern, the slower the yacht moves forward, in particular due to the large lateral force.
A sailing yacht 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 left side (1), the yacht is said to be sailing on port tack; if it is blowing to starboard (2), it is said to be sailing on 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 its sail, as shown in the figure below left. To minimize deviation to the side from a straight line, the yacht moves, changing course from starboard tack to port 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 flutters for some time, i.e. is inactive (middle picture below the text). The yacht finds itself in the so-called dead zone, losing speed until the wind again inflates the sail from the opposite direction.
Yachting: The Complete Guide Toghill Jeff
Yacht's course relative to the wind (Rumb of sailing)
Yacht's course relative to the wind: A – close-hauled, B – full-hauled, C – halfwind, D – backstay, E – favorable direction, F – jibe
Steep close-hauled (tacking). When a boat sails on a course as close (as possible) to the direction against the wind without the luff being flushed, it is said to be sailing close-hauled. Sails should be chosen as strong as possible.
Full close-hauled. With this course, the yacht tacks less. The wind does not blow straight towards or towards the stern, but into the side of the boat, so the sails should be slightly trimmed compared to a steep close-hauled wind. as much as possible until they begin to rinse.
Gulfwind. A yacht moving under sail at right angles to the wind is said to be tacking. Since the wind blows against the side, the sails are trimmed by about half.
Backstay. When the wind is blowing from behind, but not directly astern, the yacht heads backstay. The sails are etched until the luff begins to rinse. and then select enough for it to disappear. In this position the wind is blowing from the stern and the spinnaker can be raised.
Fordewind. With a fair wind, the sails are completely trimmed. They are spread out to catch as much wind as possible, the yacht goes with the wind. When the wind blows directly into the stern, the jib can flutter because the sail overlaps the trot. In this case, you can either put it on the other side, where it will fill with wind again, or lower it and install a spinnaker instead. (Large spinnakers, shaped like a parachute, can only be used when the wind is following.)
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There are two main types of sails - straight and oblique. A straight sail is a regular sail, a piece of fabric located across the hull that pulls the ship in the direction the wind blows. An oblique sail (usually triangular, but also quadrangular) allows you to use wind energy so that the ship can sail against the air flow.
In practice, it looks like this: a headwind flows around a specially tuned sail and pushes the ship forward and to the side. Thus, the yacht or boat can move in the desired direction in zigzags (tacks), exposing first one side or the other to the wind.
It was this technology that allowed sailing ships to gain a fundamentally different freedom of movement. She made reliable trade routes that previously depended entirely on favorable winds. A ship with straight sails, using a tailwind, could reach the desired place, but in order to return back, it had to wait for a change in wind direction, sometimes for many weeks. It is clear that such navigation was unreliable and unpredictable. The oblique sail partially solved this problem. The very idea of sailing against the wind is completely paradoxical! But it fully complies with the laws of physics.
Today it is difficult to establish exactly who first invented the oblique sail, but we know that this discovery came to Europe through the Arabs, who regularly visited the waters of the Indian Ocean. There they most likely saw a similar technical solution on the ships of the Polynesians. The latter could not have explored the Pacific Ocean as actively as they did if they had not had a slanting sail. However, the Chinese also widely used oblique sails.
Be that as it may, the rake sail very quickly began to spread in the Mediterranean Sea with its stable and predictable air currents. The prevailing winds here blow from southeast to northwest. And of course, for ships that had to sail in the opposite direction, this presented a problem. They solved it thanks to an oblique sail.
How did technology develop?
The first European version of this invention was the lateen sail - a triangular oblique sail attached to the side of the mast (photo 1). It made it possible to successfully sail against the wind. However, this design was very labor-intensive, since when the wind changed, the lateen sail had to be removed from one side of the mast and installed on the other side.
The invention of the gaff sail helped to cope with this problem (photo 2). This is the same oblique sail, only quadrangular and stretched not from the side of the mast, but behind it, and its upper edge (luff) is fixed to the gaff, and the lower edge (luff) is fixed to the boom - the horizontal structural elements that stretch this sail.
The gaff and boom themselves are fixed at one end to a vertical mast. Thanks to these inventions, it became much easier to move the sail from one side to the other when changing tack. By the eighteenth century, this slanting sail design had completely replaced the lateen sail.
At the beginning of the 20th century, the gaff sail was replaced by the so-called Bermuda sail (photo 3), which to this day is the most common type of sail. It originated in the Bermuda region, where it was used by local fishermen. There the Europeans “spied” the secret. And thanks to the fact that by this time aerodynamic laws had already been discovered, the Bermudian invention quickly became a leader in the sailing industry.
A Bermuda sail is a triangular sail with the luff extending along the mast and the luff extending along the boom. In terms of ease of management and efficiency, it shows the best results. These are the types of sails found on the vast majority of modern sailing yachts (photo 3).
It is worth noting that today, when we talk about a sailboat, we almost always mean a sailing yacht. Yachts and yachting are a new page in the history of sail, no less exciting than its ancient origins. But more on that next time.
Natalia Nikitina is a member of the team of the sailing school Gokova Sailing Phuket (www.gokovaphuket.ru). If you would like to try sailing, please contact the school by email [email protected].
Today we will turn our attention to the following fact: The yacht, regardless of the direction of the wind, moves where the captain and his crew lead it. This happens even when the wind is blowing in the opposite direction. Why is this happening? What is the secret of this phenomenon?
The boat with a sail appeared long before the advent of airplanes. But the principle of operation of sails and wings is the same. The basis of the work is the lifting force. But if in airplanes, the lifting force of the wing, cutting through the wind, pushes the car upward, then the sail, located vertically, pushes the yacht forward.
The headwind hitting the sail creates a pushing force. The secret is that on the windward side, the one that is internal, the wind speed is less than on the leeward side. Therefore, a vacuum is formed, and the sail is literally sucked in by air. All this is possible thanks to the features of the sail design. In other words, we can say the following: it doesn’t matter how the sail is located on the ship, because it just converts the energy of the wind. That is why the yacht is able to sail against the wind current.
Even in those moments when it seems to the viewer’s eye that the sail must certainly slow down the yacht, since the wind is blowing into it from outside, this does not happen. But this also does not happen because the center of application of forces is at the bow of the ship, and the wind easily provides a “pushing” movement.
But let's ask real yachtsmen about how and why a yacht moves, and is it true that you can sail against the wind?
Andrey Volkhov has considerable experience in managing yachts, and therefore you can trust him unconditionally. “In fact, the yacht will not be able to move against a strong wind. If you place it perpendicular to the wind flow. You can only move at a certain angle. The operation of a sail is identical to that of an airplane wing. The lift created by the wind pushes the ship forward.”
But not only lifting force occurs under wind load. Roll is another phenomenon that needs to be taken into account when steering a boat. This phenomenon not only slows down the yacht, but is also very dangerous for the entire crew. In cases where the boat is heeling, the crew must create a counterweight as quickly as possible.
Let's look at everything in more detail using the example of a sports yacht.
- Option one: the wind blows in a favorable direction. Everything here is clear and simple. The yacht moves forward without difficulty, and the crew is not burdened with significant actions.
The sail has several shapes. The Arabian shape is when the sail has an “oblique” appearance. This form is effective for side wind flows, as well as those close to oncoming ones. However, it will certainly be behind a straight sail, with a fair wind. In this case, a “staysail” would be added to the main sail (mainsail) - an additional sail. These two sails are capable of accelerating a light yacht to 30 km/h.
- The second situation is that the wind flows hit the side of the ship. Now the crew has perked up and unfurls the sail. An important part of the spar (rigid equipment of the yacht) is the boom. Rope gear is called rigging. All this serves to control the spar. Moving the ship forward is the art of yachtsmen. The main task of the crew is to turn the sail to the desired angle in time. Thus, the crew pursues one goal - to get maximum energy from the wind.
- The next situation is that the wind is blowing at an angle of 20 degrees, and this is against the movement of the boat. Beidewind - calls a move against the wind. This is what seasoned sailors called it back in ancient times. In this case, the team is as tense as possible, because it needs to catch the wind. And after a while this succeeds, and the yacht begins to move forward again. We have already examined the secret of this phenomenon. But the yacht has another sail! He is invisible!
Many have already guessed that this sail is located under the bottom of the ship. It's called a keel. Sailors usually call it a centerboard. This element is necessary in order to resist heeling, as well as restrain the force of the wind on the sail. Another ability of the centerboard is to convert heeling force into propulsion energy. The laws of physics work as accurately as possible in yacht sports.
And of course, the crew is powerless when there is no wind at all. Although...many yachts have engines, just in case of “no wind”. Therefore, you don’t have to worry about the “unforeseen death” of the wind.