Sail performance in different winds. Topic: “Physics of motion of a sailing yacht
No less important than the resistance of the hull is the traction force developed by the sails. To more clearly imagine the work of sails, let's get acquainted with the basic concepts of sail theory.
We have already talked about the main forces acting on the sails of a yacht sailing with a tailwind (jibed course) and a headwind (behind wind course). We found out that the force acting on the sails can be decomposed into the force that causes the yacht to roll and drift downwind, the drift force and the traction force (see Fig. 2 and 3).
Now let's see how the total force of wind pressure on the sails is determined and what the thrust and drift forces depend on.
To imagine the operation of a sail on sharp courses, it is convenient to first consider a flat sail (Fig. 94), which experiences wind pressure at a certain angle of attack. In this case, vortices are formed behind the sail, pressure forces arise on the windward side, and rarefaction forces arise on the leeward side. Their resulting R is directed approximately perpendicular to the plane of the sail. To properly understand the operation of a sail, it is convenient to imagine it as the resultant of two component forces: X-directed parallel to the air flow (wind) and Y-directed perpendicular to it.
The force X directed parallel to the air flow is called the drag force; It is created, in addition to the sail, also by the hull, rigging, spars and crew of the yacht.
The force Y directed perpendicular to the air flow is called lift in aerodynamics. It is this that creates thrust in the direction of movement of the yacht on sharp courses.
If, with the same drag of the sail X (Fig. 95), the lift force increases, for example, to the value Y1, then, as shown in the figure, the resultant of the lift force and drag will change by R and, accordingly, the thrust force T will increase to T1.
Such a construction makes it easy to verify that with an increase in drag X (at the same lift force), the thrust T decreases.
Thus, there are two ways to increase the traction force, and therefore the speed on sharp courses: increasing the lifting force of the sail and reducing the drag of the sail and the yacht.
In modern sailing, the lifting force of a sail is increased by giving it a concave shape with some “belliness” (Fig. 96): the size from the mast to the deepest part of the “belly” is usually 0.3-0.4 times the width of the sail, and the depth of the “belly” -about 6-10% of the width. The lifting force of such a sail is 20-25% greater than that of a completely flat sail with almost the same drag. True, a yacht with flat sails sails a little steeper into the wind. However, with potbellied sails, the speed of progress into the tack is greater due to the greater thrust.
Rice. 96. Sail profile
Note that with potbellied sails, not only the thrust increases, but also the drift force, which means that the roll and drift of yachts with potbellied sails is greater than with relatively flat ones. Therefore, a sail “bulge” of more than 6-7% in strong winds is unprofitable, since an increase in heel and drift leads to a significant increase in hull resistance and a decrease in the efficiency of the sails, which “eat up” the effect of increasing thrust. In weak winds, sails with a “belly” of 9-10% pull better, since due to the low total wind pressure on the sail, the heel is small.
Any sail at angles of attack greater than 15-20°, that is, when the yacht is heading 40-50° to the wind or more, can reduce lift and increase drag, since significant turbulence is formed on the leeward side. And since the main part of the lifting force is created by a smooth, turbulent-free flow around the leeward side of the sail, the destruction of these vortices should have a great effect.
The turbulence that forms behind the mainsail is destroyed by setting the jib (Fig. 97). The air flow entering the gap between the mainsail and the jib increases its speed (the so-called nozzle effect) and, when the jib is adjusted correctly, “licks” the vortices from the mainsail.
Rice. 97. Jib work
The profile of a soft sail is difficult to maintain constant at different angles of attack. Previously, dinghies had through battens running through the entire sail - they were made thinner within the “belly” and thicker towards the luff, where the sail is much flatter. Nowadays, through battens are installed mainly on ice boats and catamarans, where it is especially important to maintain the profile and rigidity of the sail at low angles of attack, when a regular sail is already lashing along the luff.
If the source of lift is only the sail, then drag is created by everything that ends up in the air flow flowing around the yacht. Therefore, improving the traction properties of the sail can also be achieved by reducing the drag of the yacht's hull, mast, rigging and crew. For this purpose, various types of fairings are used on the spar and rigging.
The amount of drag on a sail depends on its shape. According to the laws of aerodynamics, the drag of an aircraft wing is lower, the narrower and longer it is for the same area. That is why they try to make the sail (essentially the same wing, but placed vertically) high and narrow. This also allows you to use the upper wind.
The drag of a sail depends to a very large extent on the condition of its leading edge. The luffs of all sails should be covered tightly to prevent the possibility of vibration.
It is necessary to mention one more very important circumstance - the so-called centering of the sails.
It is known from mechanics that any force is determined by its magnitude, direction and point of application. So far we have only talked about the magnitude and direction of the forces applied to the sail. As we will see later, knowledge of the application points is of great importance for understanding the operation of sails.
Wind pressure is distributed unevenly over the surface of the sail (its front part experiences more pressure), however, to simplify comparative calculations, it is assumed that it is distributed evenly. For approximate calculations, the resultant force of wind pressure on the sails is assumed to be applied to one point; the center of gravity of the surface of the sails is taken as it when they are placed in the center plane of the yacht. This point is called the center of sail (CS).
Let's focus on the simplest graphical method for determining the position of the CPU (Fig. 98). Draw the sail area of the yacht on the required scale. Then, at the intersection of medians - lines connecting the vertices of the triangle with the midpoints of opposite sides - the center of each sail is found. Having thus obtained in the drawing the centers O and O1 of the two triangles that make up the mainsail and the staysail, draw two parallel lines OA and O1B through these centers and lay on them in opposite directions in any but the same scale as many linear units as square meters in the triangle; From the center of the mainsail the area of the jib is laid off, and from the center of the jib - the area of the mainsail. End points A and B are connected by straight line AB. Another straight line - O1O connects the centers of the triangles. At the intersection of straight lines A B and O1O there will be a common center.
Rice. 98. Graphical method of finding the center of sail
As we have already said, the drift force (we will consider it applied in the center of the sail) is counteracted by the lateral resistance force of the yacht’s hull. The lateral resistance force is considered to be applied at the center of lateral resistance (CLR). The center of lateral resistance is the center of gravity of the projection of the underwater part of the yacht onto the center plane.
The center of lateral resistance can be found by cutting out the outline of the underwater part of the yacht from thick paper and placing this model on a knife blade. When the model is balanced, lightly press it, then rotate it 90° and balance it again. The intersection of these lines gives us the center of lateral resistance.
When the yacht sails without heeling, the CP should lie on the same vertical straight line with the CB (Fig. 99). If the CP lies in front of the central station (Fig. 99, b), then the drift force, shifted forward relative to the force of lateral resistance, turns the bow of the vessel into the wind - the yacht falls away. If the CPU is behind the central station, the yacht will turn its bow to the wind, or be driven (Fig. 99, c).
Rice. 99. Yacht alignment
Both excessive adjustment to the wind, and especially stalling (improper centering) are harmful to the sailing of the yacht, as they force the helmsman to constantly work the helm to maintain straightness, and this increases hull drag and reduces the speed of the vessel. In addition, incorrect alignment leads to deterioration in controllability, and in some cases, to its complete loss.
If we center the yacht as shown in Fig. 99, and, that is, the CPU and the central control system will be on the same vertical, then the ship will be driven very strongly and it will become very difficult to control it. What's the matter? There are two main reasons here. Firstly, the true location of the CPU and central nervous system does not coincide with the theoretical one (both centers are shifted forward, but not equally).
Secondly, and this is the main thing, when heeling, the traction force of the sails and the longitudinal resistance force of the hull turn out to lie in different vertical planes (Fig. 100), it turns out like a lever that forces the yacht to be driven. The greater the roll, the more prone the vessel is to pitch.
To eliminate such adduction, the CP is placed in front of the central nervous system. The moment of traction and longitudinal resistance that arises with the roll, forcing the yacht to be driven, is compensated by the trapping moment of the drift forces and lateral resistance when the CP is located at the front. For good centering, it is necessary to place the CP in front of the CB at a distance equal to 10-18% of the length of the yacht along the waterline. The less stable the yacht is and the higher the CPU is raised above the central station, the more it needs to be moved to the bow.
In order for the yacht to have a good move, it must be centered, that is, put the CP and CB in a position in which the vessel on a close-hauled course in a light wind was completely balanced by the sails, in other words, it was stable on the course with the rudder thrown or fixed in the DP (allowed slight tendency to float in very light winds), and in stronger winds had a tendency to float. Every helmsman must be able to center the yacht correctly. On most yachts, the tendency to roll increases if the rear sails are overhauled and the front sails are loose. If the front sails are overhauled and the rear sails are damaged, the ship will sink. With an increase in the “belliness” of the mainsail, as well as poorly positioned sails, the yacht tends to be driven to a greater extent.
Rice. 100. The influence of heel on bringing the yacht into the wind
Courses relative to the wind. Modern yachts and sailing boats are in most cases equipped with oblique sails. Their distinctive feature is that the main part of the sail or all of it is located behind the mast or forestay. Due to the fact that the leading edge of the sail is pulled tightly along the mast (or by itself), the sail flows around the air flow without flushing when it is positioned at a fairly acute angle to the wind. Thanks to this (and with appropriate hull contours), the ship acquires the ability to move at an acute angle to the direction of the wind.
In Fig. 190 shows the position of the sailboat at different courses relative to the wind. An ordinary sailboat cannot sail directly against the wind - the sail in this case does not create a traction force capable of overcoming the resistance of water and air. The best racing yachts in medium winds can sail close-hauled at an angle of 35-40° to the wind direction; Usually this angle is not less than 45°. Therefore, the sailboat is forced to get to a target located directly against the wind. tacking- alternately starboard and port tack. The angle between the ship's courses on one tack and the other is called tacking angle, and the position of the vessel with its bow directly against the wind is leftist. The ability of a ship to tack and move at maximum speed directly into the wind is one of the main qualities of a sailboat.
Courses from close-hauled to halfwind, when the wind blows at 90° to the ship's port, are called sharp; from gulfwind to jibe (the wind blows directly astern) - full. Distinguish steep(course relative to the wind 90-135°) and full(135-180°) backstays, as well as close-hauled (40-60° and 60-80° to the wind, respectively).
Rice. 190. Courses of a sailing ship relative to the wind.
1 - steep close-hauled; 2 - full close-hauled; 3 - gulfwind; 4 - backstay; 5 - jibe; 6 - leftist.
Apparent wind. The air flow that flows around the sails of the yacht does not coincide with the direction true wind(relative to sushi). If the ship is moving, then a counter flow of air appears, the speed of which is equal to the speed of the ship. When there is wind, its direction relative to the ship is deviated in a certain way due to the oncoming air flow; the magnitude of the speed also changes. Thus, the total flow, called apparent wind. Its direction and speed can be obtained by adding the vectors of the true wind and the oncoming flow (Fig. 191).
Rice. 191. Apparent wind at various courses of the yacht relative to the wind.
1 - close-hauled; 2 - gulfwind; 3 - backstay; 4 - jibe.
v- speed of the yacht; v and - true wind speed; v in - apparent wind speed.
It is obvious that on a close-hauled course the apparent wind speed is the greatest, and on a gybe it is the smallest, since in the latter case the speeds of both flows are directed in exactly opposite directions.
The sails on a yacht are always set in the direction of the apparent wind. Note that the speed of the yacht does not grow in direct proportion to the wind speed, but much more slowly. Therefore, when the wind increases, the angle between the direction of the true and apparent wind decreases, and in weak winds, the speed and direction of the apparent wind differs more noticeably from the true one.
Since the forces acting on a sail as on a wing increase in proportion to the square of the speed of the flow, sailboats with minimal resistance to movement may experience a “self-acceleration” phenomenon, in which their speed exceeds the speed of the wind. These types of sailboats include ice yachts - ice boats, hydrofoil yachts, wheeled (beach) yachts and proa - narrow single-hull vessels with an outrigger float. Some of these types of vessels have recorded speeds up to three times the wind speed. So, our national iceboat speed record is 140 km/h, and it was set in a wind whose speed did not exceed 50 km/h. In passing, we note that the absolute speed record for sailing on water is significantly lower: it was set in 1981 on a specially built two-masted catamaran “Crossbau-II” and is equal to 67.3 km/h.
Conventional sailing ships, unless they are designed for planing, rarely exceed the displacement speed limit of v = 5.6 √L km/h (see Chapter I).
Forces acting on a sailing ship. There is a fundamental difference between the system of external forces acting on a sailing vessel and a vessel driven by a mechanical engine. On a motorized vessel, the thrust of the propeller - the propeller or water jet - and the force of water resistance to its movement act in the underwater part, located in the center plane and at a small distance from each other vertically.
On a sailboat, the driving force is applied high above the surface of the water and, therefore, above the line of action of the drag force. If the ship moves at an angle to the direction of the wind - close-hauled, then its sails operate according to the principle of an aerodynamic wing, discussed in Chapter II. When air flows around a sail, a vacuum is created on its leeward (convex) side, and increased pressure is created on the windward side. The sum of these pressures can be reduced to the resulting aerodynamic force A(see Fig. 192), directed approximately perpendicular to the chord of the sail profile and applied at the center of sail (CS) high above the water surface.
Rice. 192. Forces acting on the hull and sails.
According to the third law of mechanics, during steady motion of a body in a straight line, each force applied to the body (in this case, to the sails connected to the hull of the yacht through the mast, standing rigging and sheets) must be counteracted by a force equal in magnitude and oppositely directed. On a sailboat this force is the resultant hydrodynamic force H, attached to the underwater part of the hull (Fig. 192). Thus, between the forces A And H there is a known distance - the shoulder, as a result of which a moment of a pair of forces is formed, tending to rotate the ship relative to an axis oriented in a certain way in space.
To simplify the phenomena that arise during the movement of sailing ships, hydro- and aerodynamic forces and their moments are decomposed into components parallel to the main coordinate axes. Guided by Newton's third law, we can write out in pairs all the components of these forces and moments:
| A | - aerodynamic resultant force; |
| T | - the thrust force of the sails moving the ship forward: |
| D | - heeling force or drift force; |
| A v | - vertical (trimming to the nose) force; |
| P | - mass force (displacement) of the vessel; |
| M d | - trimming moment; |
| M cr | - heeling moment; |
| M P | - the moment leading to the wind; |
| H | - hydrodynamic resultant force; |
| R | - the force of water resistance to the movement of the vessel; |
| R d | - lateral force or resistance to drift; |
| H v | - vertical hydrodynamic force; |
| γ· V | - buoyancy force; |
| M l | - moment of resistance to trim; |
| M V | - restoring moment; |
| M at | - sinking moment. |
In order for the ship to move steadily along its course, each pair of forces and each pair of moments must be equal to each other. For example, the drift force D and drift resistance force R d create a heeling moment M kr, which must be balanced by the restoring torque M in or moment of lateral stability. This moment is formed due to the action of mass forces P and buoyancy of the vessel γ· V, acting on the shoulder l. The same forces form the moment of resistance to trim or the moment of longitudinal stability M l, equal in magnitude and opposing the trimming moment M d. The terms of the latter are the moments of pairs of forces T - R And A v - H v .
Thus, the movement of a sailing ship on an oblique course to the wind is associated with roll and trim, and the lateral force D, in addition to roll, also causes drift - lateral drift, so any sailing ship does not move strictly in the direction of the DP, like a ship with a mechanical engine, but with a small drift angle β. The hull of a sailboat, its keel and rudder become a hydrofoil, onto which an oncoming flow of water flows at an angle of attack equal to the angle of drift. It is this circumstance that determines the formation of a drift resistance force on the keel of the yacht R d, which is a component of the lift force.
Stability of movement and centering of a sailing vessel. Due to heel, the thrust force of the sails T and resistance force R appear to operate in different vertical planes. They form a pair of forces that drive the ship towards the wind - knocking it off the straight course it is following. This is prevented by the moment of the second pair of forces - heeling D and drift resistance forces R d, as well as a small force N on the steering wheel, which must be applied in order to correct the yacht’s movement along the course.
It is obvious that the vessel’s reaction to the action of all these forces depends both on their magnitude and on the ratio of the arms a And b on which they act. With increasing roll, the arm of the drive pair b also increases, and the leverage of the falling pair a depends on the relative position center of sail(CP - points of application of the resulting aerodynamic forces to the sails) and center of lateral resistance(CBS - points of application of the resulting hydrodynamic forces to the yacht hull).
Accurately determining the position of these points is a rather difficult task, especially when you consider that it changes depending on many factors: the ship's course relative to the wind, the cut and tuning of the sails, the list and trim of the yacht, the shape and profile of the keel and rudder, etc.
When designing and re-equipping yachts, they operate with conventional CPs and CBs, considering them located in the centers of gravity of flat figures, which represent sails set in the DP, and the outlines of the underwater part of the DP with a keel, fins and rudder (Fig. 193). The center of gravity of a triangular sail, for example, is located at the intersection of two medians, and the common center of gravity of the two sails is located on a straight line segment connecting the CP of both sails, and divides this segment in inverse proportion to their area. If the sail has a quadrangular shape, then its area is divided diagonally into two triangles and the CP is obtained as the common center of these triangles.
Rice. 193. Determination of the conditional center of sail of a yacht.
The position of the central center can be determined by balancing a template of the underwater profile of the DP, cut out of thin cardboard, on the tip of a needle. When the template is positioned horizontally, the needle will be at the conditional center point. However, this method is more or less applicable for ships with a large area of the underwater part of the wing - for traditional yachts with a long keel line, ship's boats, etc. On modern yachts, the contours of which are designed based on wing theory, the main role in creating the drag force drift is facilitated by a fin keel and a rudder, which is usually installed separately from the keel. The centers of hydrodynamic pressures on their profiles can be found quite accurately. For example, for profiles with a relative thickness δ/ b about 8% this point is at a distance of about 26% of the chord b from the incoming edge.
However, the hull of the yacht in a certain way influences the nature of the flow around the keel and rudder, and this influence varies depending on the roll, trim and speed of the vessel. In most cases, on sharp courses into the wind, the true center of gravity moves forward with respect to the center of pressure determined for the keel and rudder as for isolated profiles. Due to the uncertainty in calculating the position of the CP and the central center, when developing a design for sailing ships, designers place the CP at a certain distance a- ahead - ahead of the Central Bank. The amount of advance is determined statistically, from a comparison with well-proven yachts that have underwater contours, stability and sailing rigs close to the design. The lead is usually set as a percentage of the length of the vessel at the waterline and is 15-18% for a vessel equipped with a Bermuda sloop. L. The less stability of the yacht, the more roll it will receive under the influence of the wind and the greater the advance of the CPU in front of the central steering system is necessary.
Precise adjustment of the relative position of the CP and CB is possible when testing the yacht while underway. If the ship tends to fall into the wind, especially in medium and fresh winds, then this is a major alignment defect. The fact is that the keel deflects the flow of water flowing from it closer to the vessel’s DP. Therefore, if the rudder is straight, then its profile operates with a noticeably lower angle of attack than the keel. If, in order to compensate for the tendency of the yacht to sink, the rudder has to be shifted to the wind, then the lifting force generated on it turns out to be directed in the leeward direction - in the same direction as the drift force D on sails. Consequently, the ship will have increased drift.
Another thing is the easy tendency of the yacht to be driven. The rudder, shifted 3-4° to the leeward side, operates with the same or slightly greater angle of attack as the keel, and effectively participates in resistance to drift. Lateral force H, which occurs on the rudder, causes a significant shift of the general center of gravity towards the stern while simultaneously reducing the drift angle. However, if in order to keep the yacht on a close-hauled course you have to constantly shift the rudder to the leeward side at an angle greater than 2-3°, it is necessary to move the CPU forward or move the central steering system back, which is more difficult.
On a completed yacht, you can move the CPU forward by tilting the mast forward, moving it forward (if the step design allows), shortening the mainsail along the luff, and increasing the area of the main jib. To move the central steering wheel backwards, you need to install a fin in front of the steering wheel or increase the size of the steering blade.
To eliminate the yacht's tendency to sink, it is necessary to apply opposite measures: move the CPU back or move the central center forward.
The role of aerodynamic force components in the creation of thrust and drift. The modern theory of the operation of an oblique sail is based on the provisions of the aerodynamics of the wing, the elements of which were discussed in Chapter II. When an air flow flows around a sail set at an angle of attack α to the apparent wind, an aerodynamic force is created on it A, which can be represented in the form of two components: lift Y, directed perpendicular to the air flow (apparent wind), and drag X- force projections A on the direction of air flow. These forces are used when considering the characteristics of the sail and sailing equipment in general.
At the same time force A can be represented in the form of two other components: traction force T, directed along the axis of motion of the yacht, and the drift force perpendicular to it D. Let us recall that the direction of movement of the sailboat (or path) differs from its course by the value of the drift angle β, however, in further analysis this angle can be neglected.
If on a close-hauled course it is possible to increase the lifting force on the sail to the value Y 1, and the frontal resistance remains unchanged, then the forces Y 1 and X, added according to the rule of vector addition, form a new aerodynamic force A 1 (Fig. 194, A). Considering its new components T 1 and D 1, it can be noted that in this case, with an increase in lift, both the thrust force and the drift force increase.
Rice. 194. The role of lift and drag in creating driving force.
With a similar construction, one can be convinced that with an increase in drag on a close-hauled course, the thrust force decreases and the drift force increases. Thus, when sailing close-hauled, the lifting force of the sail plays a decisive role in creating sail thrust; drag should be minimal.
Note that on a close-hauled course the apparent wind has the highest speed, so both components of the aerodynamic force Y And X are quite large.
On a Gulfwind course (Fig. 194, b) lift is the traction force, and drag is the drift force. An increase in the drag of the sail does not affect the amount of traction force: only the drift force increases. However, since the apparent wind speed in the gulfwind is reduced compared to the close-hauled wind, drift affects the ship's performance to a lesser extent.
Backstay on course (Fig. 194, V) the sail operates at high angles of attack, at which the lifting force is significantly less than the drag. If you increase the drag, the thrust and drift force will also increase. As the lifting force increases, the thrust increases and the drift force decreases (Fig. 194, G). Consequently, on the backstay course, an increase in both lift and (or) drag increases thrust.
During a gybe course, the angle of attack of the sail is close to 90°, so the lifting force on the sail is zero, and the drag is directed along the axis of motion of the vessel and is the traction force. The drift force is zero. Therefore, on a gybe course, to increase the thrust of the sails, it is advisable to increase their drag. On racing yachts this is done by setting additional sails - a spinnaker and a blooper, which have a large area and a poorly streamlined shape. Note that on a gybe course, the yacht's sails are affected by the apparent wind of minimum speed, which causes relatively moderate forces on the sails.
Drift resistance. As shown above, the force of drift depends on the yacht's course relative to the wind. When sailing close-hauled, it is approximately three times the thrust force T, moving the ship forward; on gulfwind both forces are approximately equal; on a steep backstay, the sail thrust turns out to be 2-3 times greater than the drift force, and on a pure gybe there is no drift force at all. Consequently, in order for a sailboat to successfully move forward on courses from close-hauled to gulfwind (at an angle of 40-90° to the wind), it must have sufficient lateral resistance to drift, much greater than the resistance of the water to the movement of the yacht along the course.
The function of creating resistance to drift on modern sailing ships is mainly performed by fin keels or centerboards and rudders. The mechanics of the generation of lift on a wing with a symmetrical profile, such as keels, centerboards and rudders, was discussed in Chapter II (see page 67). Note that the drift angle of modern yachts - the angle of attack of the keel or centerboard profile - rarely exceeds 5°, therefore, when designing a keel or centerboard, it is necessary to select its optimal dimensions, shape and cross-sectional profile in order to obtain maximum lifting force with minimal drag. at low angles of attack.
Tests of aerodynamic symmetrical airfoils have shown that thicker airfoils (with a larger cross-sectional thickness ratio t to his chord b) provide greater lifting force than thin ones. However, at low speeds such profiles have higher drag. Optimal results on sailing yachts can be achieved with keel thickness t/b= 0.09÷0.12, since the lifting force on such profiles depends little on the speed of the vessel.
The maximum thickness of the profile should be located at a distance of 30 to 40% of the chord from the leading edge of the keel profile. The NACA 664-0 profile also has good qualities with a maximum thickness located at a distance of 50% of the chord from the nose (Fig. 195).
Rice. 195. Profiled keel-fin of a yacht.
| Distance from spout x, % b | ||||||
| 2,5 | 5 | 10 | 20 | 30 | 40 | |
| Ordinates y, % b | ||||||
| NACA-66; δ = 0.05 | 2,18 | 2,96 | 3,90 | 4,78 | 5,00 | 4,83 |
| 2,00 | 2,60 | 3,50 | 4,20 | 4,40 | 4,26 | |
| - | 3,40 | 5,23 | 8,72 | 10,74 | 11,85 | |
| Profile; relative thickness δ | Distance from spout x, % b | |||||
| 50 | 60 | 70 | 80 | 90 | 100 | |
| Ordinates y, % b | ||||||
| NACA-66; δ = 0.05 | 4,41 | 3,80 | 3,05 | 2,19 | 1,21 | 0,11 |
| Profile for centerboards; δ = 0.04 | 3,88 | 3,34 | 2,68 | 1,92 | 1,06 | 0,10 |
| Keel of yacht NACA 664-0; δ = 0.12 | 12,00 | 10,94 | 8,35 | 4,99 | 2,59 | 0 |
For lightweight racing dinghies capable of planing and reaching high speeds, centerboards and rudders with a thinner profile are used ( t/b= 0.044÷0.05) and geometric elongation (deepening ratio d to the middle chord b Wed) to 4.
The elongation of the keels of modern keel yachts ranges from 1 to 3, the rudders - up to 4. Most often, the keel has the form of a trapezoid with an inclined leading edge, and the angle of inclination has a certain effect on the amount of lift and drag of the keel. When extending the keel around λ = 0.6, an inclination of the leading edge of up to 50° can be allowed; at λ = 1 - about 20°; for λ > 1.5, a keel with a vertical leading edge is optimal.
The total area of the keel and rudder to effectively counteract drift is usually taken to be from 1/25 to 1/17 of the area of the main sails.
As an introduction. This article was born with the encouragement and moral support of my long-time communication colleagues on the site’s forum “Shipyard on the Table.” Its purpose was to cover, within the limited framework of the site, an extensive section of nautical practice associated with changing the sail of a ship in proportion to the strength and direction of the wind. That is why only the process of taking the reefs and cleaning the sails is described. The publication is intended for people familiar with the basic concepts and terms from the practice of arming sailing ships. In order not to repeat myself, I deliberately miss and shorten everything that has already been published on this site and related to this topic, and I will try to summarize what, in my opinion, may seem interesting to an inquisitive reader in works published mostly in Russia in the second half of the 19th century .
So, first about the wind. Yes, yes about him, because, without going into theory and detailed calculations, it is he who is the driving force of a sailing ship. In the heyday of sailing shipbuilding, sailors characterized the strength of the wind depending on the sails that could be carried while sailing close-hauled. This was explained by the fact that when taking a close-hauled course, ships are forced to carry less windage. The main reasons are that, firstly, the lateral, most dangerous from the point of view of loss of spar, effect of the sails through the covered yards on the masts and topmasts, supported by the shrouds and foreduns more from the rear than from the sides, turns out to be greater than with other courses; secondly, the lateral stability of the ship is significantly less than the longitudinal one; and thirdly, the force of the wind acting on the ship as well as other moving object depends on the direction of its movement, that is, in close-hauled conditions it increases, and with a tailwind it decreases. Therefore, with the same wind, close-hauled it was necessary to take reefs from the topsails, while the topsails could also be carried in the jibe. Based on the above, they talked about wind with top-topsails, top-topsails, topsails, reef-topsails and under-sail, when lying close-hauled you can raise the top-topsails, or go under the top-topsails, or only under the topsails or under reefed topsails, or carry only the lower topsails sail. To more accurately characterize the wind, they said, for example, the topsail wind is quiet, the topsail wind is strong, the topsail wind is gusty, etc. By calm we meant complete calm, and by storm we meant wind, in which we kept under a tightly reefed main topsail or only under the trysails. Later they moved to a more accurate determination of wind strength in points according to the Beaufort system (Table 1).
| Calculated speed per second of time | Pressure in Russian pounds per foot | Points indicating the degree of wind strength | Name of winds according to Beaufort | Name of winds according to the Chapman system |
| 10,4 | 0,28 | 1 | Light air Very weak | |
| 20,8 | 1,11 | 2 | Light wind Weak | |
| 31,2 | 2,49 | 3 | light breeze | |
| 41,6 | 4,43 | 4 | Moderate breeze Moderate | Bom-bramsel |
| 51,9 | 6,92 | 5 | Fresh breeze fresh | Bramselny |
| 62,3 | 9,97 | 6 | Strong breeze Very fresh | Marseille |
| 72,7 | 13,57 | 7 | Moderate gale Strong | Reef topsail |
| 83,1 | 17,72 | 8 | Fresch gale Very strong | Under Zeil |
| 93,5 | 22,43 | 9 | Strong gale Strong | Half-storm |
| 103,9 | 27,69 | 10 | Heavy gale Very strong | Total Storm |
| - | - | 11 | Storm Storm | |
| 124,7 | 39,88 | 12 | Hurricane Hurricane |
According to the gradually increasing wind force, the sail of the vessel was gradually reduced, usually in the following order:
The top staysails and boom topsails with boom jib were stowed;
They fastened the topsails or, leaving the last ones, took one reef from the topsails;
They took a second reef from the topsails, and usually attached topsails;
They took the third reef from the topsails and replaced the fore-topmast jib with a jib, while trying to hold the jib as long as possible;
We fastened the cruise, took the last reef from the fore and main topsails, took one reef from the mizzen;
The foretopsail was fastened and the last reef was taken from the mizzen (or a storm mizzen was installed), the foretopmastsail was replaced by the foresail staysail.
The lower sails were usually reefed in the following sequence: together with the fourth reef from the topsails, they took the first reef from the mainsail, then the second reef from the mainsail and the first from the foresail, then the second from the foresail and secured the mainsail or replaced it with a mainsail trysail, and, as a last resort, when the force of the wind and waves made it impossible to move and forced her to stay under the main topsail, the foresail was secured.
With fair winds, the procedure for gradually retracting the sails was assumed to be similar to that stated above, with the only difference being that to reduce yaw rate, the mizzen was removed from the backstay and the cruise was attached while taking the third reef from the other topsails.
Thus, close-hauled storm sails on ships with square rigs usually consisted of a dully reefed main topsail (a sail was said to be dully reefed if all four reefs were taken from it), a foresail staysail and a reefed mizzen. When jibed, these were usually fore-topmasts, jib, reefed main-topsail and foresail. The main topsail is needed as a sail from which the waves rising from behind do not take away much wind, the foresail moves the overall center of sail forward, and the fore topmast is a staysail to compensate for occasional strong yaw.
As an illustrative example, I cite a lithograph by T. G. Dutton. It (Fig. 1) shows the barque Constance running backstay in a reef-topsail wind under three sails: a fore-topmast with a staysail, a foresail and a main-topsail, taken on two reefs; the crew at this time removes the fore-topsail and mainsail. At the same time, the corresponding foils are raised above the yards to make room for laying the sails.
Rice. 1. Bark Constance, running backstay.
It is impossible not to mention that the number of sails installed depends not only on the strength of the wind and its direction relative to the ship's course, but also on the magnitude of the waves, the personal experience of the captain, the characteristics and properties of a particular ship and some other factors. A significant role is played by the timeliness of making a decision to change the sail when the wind force changes: a premature reduction in the sail leads to loss of speed, and overexposure can make cleaning the sails and taking reefs difficult and dangerous for the topsailers.
In order to be able to take sails to reefs, during the rigging process, reef lines, reef lines and reef lines are threaded into the sails; Krengels and spruits are tied in, legs and collars are sewn on, benzels and bayonet bolts are threaded through. A more detailed consideration of this issue may undoubtedly be of interest from the point of view of making ship models.
Reef seasons usually consisted of five fish. They were hung over a pole and from the long ends they wove a braid long enough to form a double point, which was necessary so that the threaded reefs could not slip through the grommet of the sail (Fig. 2). Then the woven part was hung in the middle through the pole, one end was made around the pole to form a double point, both ends were connected and the sesen continued to be woven from the shkims of both halves. (Fig. 3). The ends of the seams were wrapped with a sailing thread and girded, stitched through. The length of the reef-sezny must correspond to the thickness of the yard, and since the reef was tied on the yard as high as possible, the rear halves of the sezny were usually made longer than the front ones, with the exception of the sezny of the fourth reef, in which, on the contrary, the front ends were made longer than the rear, due to the fact that the bayonet bolt The fourth reef was taken, as a rule, from behind the yardarm and the reef itself was fitted under the bottom of the yardarm. During the rigging process, the reef sails were threaded while sitting on the floor by two people, one on each side of the outstretched sail. Each, taking one half of the reef season, passed its end into the grommet, at the same time accepting the other end of the season from his colleague and passed it into the point of his half. Next, an ordinary pulley was put on the end of the sesen; people each grabbed their end with their hands, rested their feet on the pulleys and thus tightly pulled the sesen, securely fastening it in the grommet. When taking reefs, the canvas between the yard and the corresponding reef bow was rolled up and the resulting roll was tied with a straight reef bow (Fig. 4) or a reef knot (Fig. 5).
Rice. 2 - 5. Reef seasons.
In the second half of the 19th century, one or two reef ropes began to be inserted through the eyelets in the reef bow using one of the methods shown below (Fig. 6). To prevent the half-bayonets of the reefers from weakening, benzels made of skimushgar were placed on them.
Rice. 6 and 7. Reef line wiring.
Reef lines with brakes were secured on a rod rail used to tie the sail, or on a special rail mounted behind the sail line, or were carried around the yard (Fig. 8) (on topsail yard they were attached in pairs - one for 1st and 3rd -th reef, second for the 2nd and 4th). When taking such a reef, the canvas was picked up to the corresponding reef bow, the end of the reef rope was passed into the loop of the reef rope and closed on the brake (Fig. 9).
Rice. 8 and 9. Reef seasons.
When taking such a reef, the flesh was not touched, but was left hanging between the sail and the yard.
The reef lines of trysails and mizzens were cut out of white cable and sewn into the sail in a slightly different way. Here's one way: they made a hole in the sail where the reef thread was threaded, threaded it through and aligned the ends on both sides of the sail. Then the sesen was unwound close to the sail so that the strands unfurled and formed pegs in loops. These loops were sewn to the sail, and a little lower they quilted both parts of the canvas and the sails all the way through. The ends of the seams were wrapped with sailing thread and also quilted through for strength.
Reef pins, also called snakes, served to conveniently attract the sail to the yard when taking reefs. They were a thin rope, one end of which was molded to the luff grommet; the other end went down the front side of the sail and was grabbed onto the necks of the corresponding reef seasons up to the fourth reef (Fig. 7). The lower sails had from 6 to 8 snakes, the topsails had 6, (on small ships 4), the cruisers had 4.
Interdistrict scientific and practical conference “Step into the future”Section: physics
Topic: “Physics of motion of a sailing yacht”
Head: Buholtseva O.V., physics teacher
Municipal educational institution secondary school No. 11, Severobaykalsk
Severobaykalsk
We want to pay attention to the relevance of training for beginners: 2
Novelty 3
Yachts of Severobaykalsk 3
Physics 4
Wind motive force 4
Bernoulli's Law 4
Jibe course 5
Gulfwind course 6
Weight location and water-hull interaction 7
Longitudinal weight distribution. Spicy courses 8
Longitudinal weight distribution. Complete courses 8
Lateral weight distribution with tailwind 9
Transverse weight distribution with tailwind and wave 9
Conclusion 11
We have been sailing for 10 years. At first we sailed on Optimists, over time we gained experience and began sailing on Luch-mini and Cadet class yachts. Now, having become older and even more experienced, we can manage a Luch-standard class yacht and cruising vessels. Participated in regional regattas in Severobaikalsk, Bratsk and Ust-Ilimsk. Repeatedly took prizes and were winners.
We want to pay attention to the relevance of training for beginners:
In the summer, at the Baikal Regatta camp, we, the “old men,” teach sailing to beginners. Training time is 21 days. And here the future yachtsman understands how important knowledge of physics is, and not intuition. After all, every “beginner” believes that the main thing in movement is the wind and preferably a tailwind. This is the first and big mistake. And there are many of them. Therefore, the goal of our work is to create a manual for studying the physics of motion of a sailing yacht.To achieve the goal, we need to solve the followingtasks :
Consider the types of yachts that are available in Severobaykalsk.
Study the nature of the yacht's movement.
Challenge the newcomers' point of view that tailwind is the most important thing.
Study how weight placement affects the speed of a yacht.
Consider the influence of the physical characteristics of water on the speed of the yacht.
Collection and analysis of information.
Interview and survey.
Perform calculations.
Compiling tables.
Yacht testing.
Novelty
In books and on websites there is a description of the physics of the yacht’s movement, but in all these materials each factor influencing the movement of the yacht, namely the interaction of the wind with the sail, the distribution of weight over the yacht, the interaction of water with the hull, is considered separately, which, in our opinion , wrong. After all, to win, a yachtsman must combine these three factors into a single whole.Yachts of Severobaykalsk
There are some classes of yachts available in Severobaykalsk, such as:|
Name |
Displacement |
Length |
Windage |
Crew |
|
Ray |
≈ 160 kg |
4.23 m |
7.05 m2 |
1 person |
|
Optimist |
emergency buoyancy of at least 90 liters |
≈ 2.3 m |
3.33 m2 |
1 person |
|
Finn |
107kg |
4.50m |
10 m 2 |
1 person |
|
Cadet |
95kg |
3.22 m |
9.41 m2 |
2 people |
|
Assol |
630kg |
5.53m |
13.66 m2 |
4 people |
http://minitonnik.com.ua/?q=node/126
Physics
Wind driving force
The movement of the yacht occurs due to the fact that the wind interacts with the sail. Analysis of this interaction leads to unexpected results for many beginners. It turns out that the maximum speed is achieved not at all when the wind blows directly from behind, and the wish for a “fair wind” carries a completely unexpected meaning.Both the sail and the keel, when interacting with the flow of air or water, respectively, create lift, therefore, to optimize their operation, wing theory can be applied.
Bernoulli's law
The air flow has kinetic energy and, interacting with the sails, is capable of moving the yacht. The work of both the sail and the airplane wing is described by Bernoulli's law, according to which an increase in flow speed leads to a decrease in pressure. When moving in the air, the wing divides the flow. Part of it goes around the wing from above, part from below. An airplane wing is designed so that the air flow over the top of the wing moves faster than the air flow under the bottom of the wing. As a result, the pressure above the wing is much lower than below. The pressure difference is the lift of the wing.
The sail can move the yacht only if it is at a certain angle to the flow and deflects it. The question remains: how much of the lift is due to the Bernoulli effect and how much is the result of flow deflection. According to classical wing theory, lift arises solely as a result of the difference in flow velocities above and below an asymmetrical wing. It is well known that a symmetrical wing is capable of creating lift if installed at a certain angle to the flow. In both cases, the angle between the line connecting the front and rear points of the wing and the direction of the flow is called the angle of attack.
Lift increases with increasing angle of attack, but this relationship only works at small values of this angle. As soon as the angle of attack exceeds a certain critical level and the flow stalls, numerous vortices are formed on the upper surface of the wing, and the lift force decreases sharply.
The sail, being at an angle to the air flow, deflects it. Coming through the “upper”, leeward side of the sail, the air flow travels a longer path and, in accordance with the principle of flow continuity, moves faster than from the windward, “lower” side. As a result, the pressure on the leeward side of the sail is much lower than on its windward side.
Jib course
When moving on course jibe When the sail is set perpendicular to the direction of the wind, the degree of increase in pressure on the windward side is greater than the degree of decrease in pressure on the leeward side, in other words the wind pushes the yacht more, than pulls. As the yacht turns sharper into the wind, this ratio will change. Thus, if the wind is blowing perpendicular to the yacht's course, increasing the pressure on the sail on the windward side has less effect on speed than decreasing the pressure on the leeward side. As a result, with this course, the sail pulls the yacht more than it pushes.Yachtsmen know that gybe is not the fastest course. If the wind of the same strength blows at an angle of 90 degrees to the heading, the yacht moves much faster. On a jibe course, the force with which the wind presses on the sail depends on the speed of the yacht. As speed increases, the pressure on the sail drops and becomes minimal when the yacht reaches maximum speed. The maximum speed on a gybe course is always less than the wind speed. There are several reasons for this: firstly, friction; during any movement, some part of the energy is spent on overcoming various forces that impede movement. But the main thing is that the force with which the wind presses on the sail is proportional to the square of the speed of the apparent wind, and the speed of the apparent wind on a gybe course is equal to the difference between the speed of the true wind and the speed of the yacht.
Gulfwind course
With a gulfwind course (at 90º to the wind), sailing yachts are able to move faster than the wind. Let us only note that on a gulfwind course, the force with which the wind presses on the sails depends to a lesser extent on the speed of the yacht.
Weight placement and water-hull interaction
It is useful for everyone to pay attention to the effect that weight distribution has in a given situation. Every time we offer to talk about setting up a yacht, beginners are sure that we will talk about the spar and sails. But there is an area that is rarely remembered - this is the position of the hull in the water - how to “balance”, “trim the ship”, “correctly distribute ballast on the ship”.Obviously, proper weight distribution can play a decisive role in determining the yacht's finishing position. This problem can be solved by transferring weight to one point or another on the yacht.
The main principle of balancing a yacht is to find a balance of forces acting on the hull and maintain the position of the hull in a state that will provide maximum speed under certain weather conditions.
Longitudinal weight distribution. Spicy courses
Light breeze
A common problem in light winds is the reduced tendency of the boat to pitch. This makes it difficult to track changes in lift and stay as close to the wind as possible. In light winds, the position of the sails and rigging reduces the tendency to roll and leaves boaters without the sensation they are accustomed to. The classic solution to this problem is to heel the yacht to leeward to change the shape of the underwater part and increase the tendency to roll. Unfortunately for most hulls this step increases the wetted surface area of the hull and also increases stern drag and consequently reduces the yacht's speed. If you instead shift your weight forward and load the nose, the center of lateral resistance will move forward, the tendency to adduct will increase, and the wetted surface area will remain the same. Obviously, by using heel to windward, the helmsman is simply increasing hull drag.
Fresh breeze
Longitudinal weight distribution. Full courses
Light breeze
The length of the waterline is one of the most important parameters that determines the speed of displacement hulls. As a result of the deepening of the bow, the stern may rise, and this will sharply reduce the length of the waterline. (In light winds, the length of the waterline is less important than the wetted surface area.) If you're sitting comfortably, chances are you haven't moved forward enough. Look at the water astern: if you see turbulence in the flow, move forward.
Medium wind
If you take into account the effect that waves create, moving forward and backward can greatly help maintain planing.
Strong wind
Lateral weight distribution with tailwind
Light wind
If the wind is strong enough, you can perform the following trick while gybeing.
Move forward as far as possible and tilt the boat a few degrees into the wind, keeping the helm on the desired course. At first you will feel a slight pull from the rudder, but as soon as the centerboard begins to generate lift, the pressure will decrease and the rudder will become light, neutral, and set in the desired direction. This turn is also very effective because it allows you to gain additional height downwind. But be careful: if during such a maneuver a wave appears that dampens the speed, the effect can be catastrophic.
Medium wind
On modern yachts there are many techniques that can be used to reduce the tendency to roll. But if you make the yacht heel to windward, the problem will disappear.
Lateral weight distribution with tailwind and wave
BackstayWhen sailing full courses in heavy seas, the shape of the hull should be used to facilitate control of the yacht. In order to ride a passing wave and prevent excessive roll, it is necessary to move the steering wheel sharply, and this reduces the chances of success.
Falling off
If we consider the forces acting on the boat, it becomes clear why the bow of the boat goes into the water when it sinks. The roll creates a lifting force on the steering wheel, which causes the nose to sink and makes it more difficult to fall away. To compensate for this, the mainsheet must be loosened and the bow will begin to move downwind. Fine course correction can be done with the steering wheel. During a turn, it is better to shift the team's weight back; As a result, the nose will rise, and this will help the wind to turn it in the desired direction.
Tack
I know from experience sailing small dinghies that speed can drop dramatically during a turn. One of the reasons for this is the movement of the helmsman in the cockpit. Diving under the boom during a turn, the helmsman moves back, lowers the stern, and it begins to work as a good brake. You can correct the situation if you walk around the shoulder straps facing backwards. At the same time, the center of gravity does not shift so far back, because the “fifth fulcrum” is heavier than the head! This is an effective maneuver, but be careful when avoiding the boom and don't bend too much - one move of your leg and the effect of your action is gone. (When preparing the text, this recommendation raised serious doubts. After all, when transferring facing backwards, the helmsman loses orientation and control over what is happening around. We invite readers to make an independent decision about which method is better. - Note from translators.)
So, how do we distribute the weight:
|
Light breeze |
Medium wind |
Fresh breeze |
|
· Move forward until you feel comfortable; · do not heel the yacht to leeward, it is better to move forward. |
· remember that the steering wheel is a brake. Try to keep it in the middle position, change the course by working with the sails; · as soon as the yacht begins to plan, move back; as soon as the yacht goes into displacement mode, move forward; · when falling off, move backwards and begin the maneuver by releasing the sheets. |
· on full courses, keep the bow of the yacht as high above the water as possible; · on sharp courses, if you move too far back, the yacht will slow down with its stern; if you move too far forward, the yacht will yaw on the wave. |
The main factor that prevents an increase in speed is friction. Therefore, sailboats with little resistance to movement are able to reach speeds much higher than the speed of the wind, but not on a gybe course. For example, a boat, due to the fact that skates have negligible sliding resistance, is capable of accelerating to a speed of 150 km/h with a wind speed of 50 km/h or even less.
Conclusion
Conclusion: the city of Severobaikalsk is located on the shore of Lake Baikal; in the water area there is the only yacht club in Buryatia, which is a local attraction for tourists and schoolchildren. During the short northern summer, many of them dream of learning to sail on yachts. While studying the yacht's equipment can be done on shore, the theoretical course on the physics of yacht motion is difficult to master. And this manual will help everyone correctly distribute weight, adjust the sail and choose a course according to their physical characteristics and skills.
Apparent wind
Let's try to understand due to what forces, and on the basis of what principles, the movement of a sailing ship occurs under the influence of the wind. Let's consider only oblique sails, as they are the most common at present. The Bermuda-type oblique sail rig is the main rig of most modern single-mast and two-mast vessels. All sport and cruising single-mast yachts are also armed with a Bermuda sloop.
This rig provides maximum opportunities for choosing a course relative to the direction of the wind and requires a significantly smaller crew to control the sails and does not require such a high level of training as in the case of using direct sailing rigs.
A remarkable feature of an oblique sail is its ability to create traction on courses up to 30-40 degrees to the wind direction.
It must be taken into account that the sailing vessel is moving relative to the apparent or apparent wind, and not relative to the true or meteorological wind.
When any object moves in the air, a flow of incoming air arises, the speed of which is determined by the speed of the object. Accordingly, even in the complete absence of wind (calm), an observer on the ship will feel a wind equal to the speed of the ship - a heading wind, which will be equal in magnitude to the speed of the ship, and in the direction opposite to the direction of movement of the ship. Thus, a sailing ship, when moving, experiences the action of two air flows:
The action of a flow caused by the presence of a true wind;
The action of the flow caused by the movement of the vessel - directional wind.
To determine the resulting air flow felt by an observer located on a moving object, it is necessary to perform a vector addition of the flows. The resulting vector will be the speed and direction of the felt or apparent wind, which is called the apparent wind. This wind will be considered as the wind acting on the sails of the ship as it moves (Fig. 1).
This wind is the only wind with which the sails interact, and its decomposition into true wind and directional wind is the result of an analysis of the original air flows.
Apparent wind is a variable value even when the true wind is stable in speed and direction, since its speed and direction depend on the speed and direction of the ship's movement. For simplicity of reasoning, let us consider the case in which Fig. 1.
the true wind is directed at right angles to the direction of movement of the vessel and the speed of the true wind is equal to the speed of the vessel (Fig. 2). The figure shows that when moving at an angle of 90 degrees to the true wind, the ship is moving at an angle of 45 degrees to the apparent wind.
true In accordance with the above, you can
wind apparent wind assert that two vessels moving at the same
him 
and the same course, with the same wind conditions
conditions, but with different speeds relative to the water, they will move at different angles to the apparent wind. A vessel moving at a higher speed will sail sharper into the apparent wind while maintaining the same heading angle relative to the true wind. At the same time, wind indicators will be located on the masts of these ships.
the directional wind is at different angles to the ship's DP, fixing the direction
rice. 2 the apparent wind of each vessel (Fig. 3).
ship 1 ship 2
It can be seen from the figure that a ship traveling at a higher speed moves at a smaller angle to the apparent wind. From this we can conclude that as the speed of the vessel increases, the apparent wind sets in (the angle between the direction of the vessel’s movement and the apparent wind decreases). With a further increase in the speed of the vessel (better lines, less friction, sails work more efficiently, a different design of the vessel's hull), the angle between the direction of the vessel's movement and the apparent wind will become less than the minimum tacking angle (the minimum angle between the direction of the vessel's movement and the apparent wind, at which the possibility of effective sail operation). After this, the vessel, which has a high speed, will be forced to fall off (increase the angle between the direction of the vessel's movement and the direction of the apparent wind) until the minimum tacking angle is restored. This explains the different windward angles (the angle between the direction of the true wind and the direction the ship is moving). At the same time, the speed of approaching the wind (the speed of approaching the point of arrival located in the wind) can be greater for a vessel with a large angle of approach to the wind, but also a higher speed. As an example, consider the speed at which a keel yacht, a sports dinghy and a catamaran go out to wind (Fig. 4).
A keel yacht, which has the lowest speed of all these vessels, moves sharper into the wind. Behind it comes a sports dinghy and the sports catamaran, which is least sensitive to the true wind. Each of these ships sails at the same angle to the apparent wind, but at different angles to the true wind. But at the same time, a sports catamaran will have the highest speed when going into the wind. From considering the speed triangle, it becomes clear that it is possible to reduce gusts of wind to true wind (short-term wind acceleration). In a gust, the speed of the true wind increases, but the speed of the ship remains, for some time, the same. The apparent wind moves away and it becomes possible to settle down and restore the tacking angle relative to the apparent wind (Fig. 5)
rice. 4
Keel yacht
dinghy
Catamaran
 |
After some time, the ship's speed will increase, and it will be forced to fall back to its previous course relative to the true wind, maintaining an angle relative to the apparent wind. However, an increase in the speed of the vessel is possible until the speed limit for the vessel's movement in displacement mode is reached (the speed of the vessel in displacement mode, expressed in knots, cannot exceed the length of the vessel, expressed in meters). Consequently, with a further increase in wind speed, the ship's speed will not increase and the ship's course relative to the true wind may be sharper.
The presence of currents in the area where the vessel is sailing is very important from the point of view of the behavior of the apparent wind. When sailing in a current, the speed of the vessel is vectorially added to the speed of the current. As a result, the absolute speed of the vessel changes and the speed and direction of the apparent wind changes. When moving with a tailwind, the apparent wind enters, and when moving with a countercurrent, it moves away. Consequently, with a tailwind, the tacking angle increases, and with a headwind, it decreases. At the same time, the speed of the yacht going into the wind remains almost unchanged. When the current is directed in the direction or against the direction of the true wind, a change in the speed of the true wind occurs. When the wind and current are unidirectional, the apparent wind enters, and when it is multidirectional, it moves away due to an increase in the speed of the true wind. The interaction of wind and current will change the ship's tacking angles relative to the true wind.
Modern navigation equipment makes it possible to obtain information not only about the direction and strength of the apparent wind, but also about the strength and direction of the true wind, by recalculating the speed triangle (Fig. 1). GPS provides information about the speed and direction of the vessel's movement, and an anemometer provides information about the speed and direction of the apparent wind. By recalculating the speed triangle, the system obtains information about the speed and direction of the true wind.
Understanding the behavior of apparent wind is key to planning a ship's route, given the known direction and speed of the true wind and the actual speed of the sailing vessel.
However, for slow-moving ships, the angle between the direction of the true and apparent wind is insignificant and it can be stated, with a certain degree of accuracy, that this angle is within 10-20 degrees.
