sail
A sail (from Old High German segal, probably originally: cut piece of cloth) is a cloth that is used to propel vehicles through the wind .
Depending on the construction and function, sails are divided into different groups. The two main groups are called square sails and pitch sails . Sails move a vehicle by taking advantage of wind pressure . It acts as pressure on the side facing the wind and as a pull or suction on the side facing away from the wind. The forces on both sides work together. Sailing vehicles can also drive diagonally against the wind with the appropriate sail position.
There have been significant developments in the material for sailcloth . While sails used to be made from vegetable tissue and later from woven synthetic fibers, laminate sails based on plastic films are currently also used.
Square sail on a replica of a medieval Kraweel
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Development history
A constant main motive in the long history of the development of the sailing ship was the endeavor not only to make sailing safer and more reliable, but also to use the forces of nature more effectively and thus move forward faster. The increasing demands on the control of water and wind even under unfavorable conditions and the specialization of shipping for the purposes of fishing, transport or military expansion required not only new constructions of boats and ships, but also the constant development and improvement of their propulsion . The use of wind energy by means of sails proved to be advantageous compared to the ship driven only by rowing , even if it could not completely replace it for a long time. The mostly empirical knowledge about the use of sails and their improvement gave rise to the profession of sailmaker , who specialized in processing the raw materials available in each case into suitable cloths. It was only in the last 100 years or so that it was possible to clarify the physics of sailing on a scientific basis and, together with the development and use of plastics, to achieve significant technological advances again. In the meantime, however, a number of sail materials and shapes have proven themselves across cultures and are still in use today.
The first known representation of a sail is on an Egyptian funeral urn from Luxor from the time 5000 BC. To find. The Egyptians used ships with a mast and a large square sail primarily for trips on the Nile , but also for trips across the Mediterranean and the Red Sea .
The development of sail shapes was closely linked to the development of the ship's hull . In early times, when the underwater part of the ship's hull was still flat (the lateral plan was small), ships were easily driven off by forces acting from the side . Therefore, the wind could only be used when it hit the ship from aft (rear) as much as possible.
With the enlargement of the lateral plan by the keel and sword , which effectively reduced the ship drifting sideways, it was possible to use other sail shapes. In the 2nd century BC The first sling sails appeared in the Greco - Roman shipping with the spritsail . In late antiquity (2nd – 4th century AD) the latin sail followed , which - initially used on smaller Roman watercraft - almost completely displaced the square sail from the Mediterranean by the transition to the Middle Ages . Sprietsails and latin sails were the first sails that were no longer run across, but in the direction of the ship's longitudinal axis (Schratsegel). This made it possible for the first time to sail diagonally against the wind and gain space to windward .
From the latin sail, the gaff sail developed over the lug sail in the 17th century . From this, in turn, the triangular high sail , which is still common today, arose in the 19th century , which enables inexpensive upwind courses .
From the middle of the 19th century, sails underwent further developments in terms of the variety of types and materials used for sailcloth through prestigious sailing regattas such as the America's Cup . Today, not only racing yachts, but also cruising yachts and boats, a variety of sail types and materials for all wind directions and wind strengths are available.
Classification and definitions
Sails are assigned to different groups of sails, depending on their construction and use. For example, the jib of a dinghy falls into the groups of pitched sail , staysail , main sail and headsail . Belonging to a group ( e.g. main sail ) does not exclude belonging to other groups (such as headsails ).
- Square sails are square sails that are attached to a horizontal rod (the yard ) attachedto the ship's mast transversely to the ship's longitudinal direction. They are the oldest known sails. Today you can practically only see them on traditionally rigged ships. The advantage of these sails lies in their ease of manufacture and their good properties on downwind and downwind courses .
- Schratsails are triangular or square sails that are set in the longitudinal direction of the ship. The modern luff sails areattached tothe mast or a stay with their luff (the leading edge) in the midship plane. In the latter case, they are also known as staysails . The great advantage of these sails is that theycan be used tosail diagonally against the wind. The stay on the stay is mostly done nowadays by means of a stay rider or a leech rope sewn into the sail, which is inserted into the groove of a profile stay.
- Main sails or working sails are the sails that are normally set upwind and are part of the basic equipment of the respective boat or ship. For a ketch or yawl , for example, these are jib , mainsail and mizzen sails .
- Side sails are those sails that are used instead of or in addition to the main sails . They are set in special wind conditions (light wind or storm) or on certain courses to the wind . One of the most famous sails is the spinnaker .
- For multi-mast sailing ships, all sails that are in front of the main mast or on the bowsprit are referred to as headsails . For example, on a slup-rigged sailing yacht, these are the jib, genoa and spinnaker.
Sail types
There is a not inconsiderable number of different types of sails, whereby the same types of sails are sometimes referred to differently. An explanatory list can be found in the main article.
Construction and equipment of the sail
The head
In triangular sails, the head is the upper corner of the sail. On modern boats , it is reinforced by the headboard (also known as the headboard ) made of wood , light metal or plastic. The halyard, which is used to raise the sail, is attached to the head. In the case of the square square and gaff sails, the upper edge of the sail is called the head.
The neck
In triangular sails, the neck is the lower front corner of the sail. In these sails it is reinforced by the butt joint . In the case of a spinnaker, that corner of the sail is considered to be the neck in which the spinnaker pole is picked (attached by means of a device). Not to be confused with the neck of sub sails ( square sails ), which is not a part of the sail, but rope.
The clew
The clew is the rear, lower corner of the sail in Schratsaileln. In square sails, the clews are the lower corners to which the sheets - and in the case of lower sails, also the necks - are attached. As a rule, sails are particularly reinforced at this corner, as great forces occur there.
Neck
Gaff topsail (fore-) are often on the neck , that is approximately midway between the head and neck, with the Neckfall additionally to mast or spar attached, if not traditionally hanks o. Ä. to be used.
The Lieken
The edges of the sails are called leeches . With triangular sails, three leeches are distinguished: the luff (on the main sail on the mast, hence also called the mast leech ), the foot leech (on the mainsail also called the leech , on the headsail as the foot leech ) and the leech . On the mainsail, the fore and foot leech are often reinforced with a luff rope or a luff wire to prevent the sail from tearing and stretching. Often there is a line in the leech that can be used to change the leech tension and thus trim the sail . The foresail only has a sewn-in luff rope in the luff, which today consists of steel wire.
With the gaff sail , the leech on the gaff is called the upper leech or gaff leech . When Rahsegel the hoist located on the Rah is Rahliek mentioned, the two lateral Lieken be as starboard or Backbordliek or as luffs designated.
The sailing tracks
The sail tracks (called clothes by the sailmaker ) are strips of cloth from which the sail is sewn or glued together. The necessary camber of the sail (with sloping sails) is achieved by cutting the individual panels accordingly. In the case of square sails with a rectangular cut, the tracks run perpendicular to the yard. In triangular sails of dinghies and yachts they usually run perpendicular to the leech chord (horizontal section) or along the load lines (bi- or tri-radial section), see sail sections .
The Cunningham throat
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The Cunningham thimble is located near the luff in the lower part of the sail and is used to trim the sail. By stretching the luff (pulling it down towards the neck) the curvature (the belly ) of the sail moves forward and the sail profile becomes flatter overall.
The battens
The sail battens are narrow, flexible battens made of ash wood or plastic that are inserted into the batten pockets provided. They are used to shape the sail and are intended to support the leech so that the rear part of the sail does not kill (flutter). With the batten sail, the battens run continuously from the mast to the leech.
The reef thimbles, reef gates and reef laces
For reefing a sail furling means Bindereffs existing in the respective Reffreihe be reef point and the Reffgattchen and Reffbändsel used. A mainsail with a furling system that is rolled into the mast or boom for reefing, on the other hand, has no reefing rows.
Materials for sails
A number of requirements are placed on the material of sails: It should be impermeable to air, tear-proof, dimensionally stable, resistant to UV radiation and seawater, it should have low water absorption and be light. Sailcloth should also be easy to process and as inexpensive as possible. Depending on the intended use, different selection criteria come to the fore. For example, the question of cost is more important for propelling a small coastal fishing boat than for a high-performance regatta sail.
In the past sails consisted mainly of vegetable tissue, but also of animal skins, as in the sails of the Eskimos. Today sails are mainly made of synthetic fibers.
Natural materials
In the past, fabric and cloth made from almost every available natural fiber were used as material for sails . Even today, sails made of all possible locally available materials are in use for small boats in poorer parts of the world. However, animal fibers are rarely used.
It is known from " Ancient China " that in the early 15th century the sails of the so-called treasure ships were made of red silk . Nordic longships were often sailed with wool sails , whereby the natural fat content of the wool of a special long-haired breed of sheep is said to have prevented the sails from absorbing too much water. In Scandinavia , nettle was also widely used for sails.
In southern areas, such as in Polynesia , sails made of braided palm leaf or pandan leaf strips were used for traditional outrigger boats until the 20th century .
In the past, sailcloth was mainly made from hemp or linen , if these materials were available. At the beginning of the 19th century, hemp and linen were slowly replaced as canvas material by the cheaper cotton , also because the sails became larger and cotton sails are lighter (cotton can be twisted much finer and more tightly woven) than linen or hemp sails. The cotton sails are also less porous, so these sails hold the wind better and they hold their shape better.
Sports sailors used tightly woven cotton sails for their boats until the introduction of synthetic sailcloth. In addition to the lower dimensional stability cotton sails have the disadvantage that they can not be stored folded moist, otherwise it by mold harden . The lee ropes, made of natural fibers, also swelled when wet and were difficult to move in the respective keep .
Sails made of natural fibers are still used today by some traditional sailors. Otherwise, these materials have been replaced by man-made fibers , as these do not rot, wear out more slowly and have better dimensional stability (less stretch ).
Artificial materials
Modern sails can be roughly divided into three types:
- Sails made of woven sailcloth , for example polyester (brand name: Dacron ), in a wide variety of qualities and designs;
- Laminate sails (sometimes referred to as sandwich sails ), in which fibers, so-called scrims, are glued together with foils or polyester fabric;
- Membrane sails - these are laminate sails in which reinforcing fibers are welded in during the production of the sail according to the expected load lines.
The following is a list of various synthetic fibers used today for the manufacture of sails:
Polyamide (brand name: nylon)
The strengths of the material lie in its low weight and relatively high strength. The great elasticity can be seen as a weakness.
Target group: Cloth for spinnakers and cruising gennakers
Polyester (brand names: Dacron , Diolen, Trevira, Terylene, Tetoron, Pentex, Mylar)
The great advantages of the material are its robustness and durability. There is a large selection of fabric weights and qualities. Disadvantages are the low dimensional stability and the relatively high stretch.
Target group: regatta and cruising sailors
Polyethylene naphthalate (PEN, brand name: PenTex)
The material is twice as stretch-resistant as polyester and is priced between polyester and aramid. It is not available as a woven cloth, but only as a scrim in the laminate.
Target group: frequent sailors in the cruising and regatta area
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Thermotropic liquid crystal polymer (TLCP, brand name: Vectran )
Vectran has mechanical properties similar to aramid, but is more durable. However, it is sensitive to UV rays. Target group: Cruising and cruising regatta sailors at the highest level
Aramid (brand names: Kevlar 29, Twaron, Technora Black)
Kevlar has a higher tensile strength than steel and is the first high-tech fiber in the sailing area. The weaknesses are the kink and UV sensitivity.
Target group: regatta sailors
High-modulus aramid (brand names: Kevlar 49, Kevlar Edge, Twaron HM)
The material is extremely low-stretch, but kink and UV-sensitive.
Target group: top regatta sailors
Ultra-
high molecular weight polyethylene (PE-UHMW, brand names: Spectra, Dyneema )
The strengths of the material lie in its high breaking load, easy handling and good UV resistance. It shows a low, profile-changing long-term stretch.
Target group: long-distance sailors
Carbon fiber (Carbon)
The material is light, has little elongation and is resistant to UV radiation. But there are big differences in quality, sails made of carbon fibers are very sensitive to kinks and are expensive.
Target group: top regatta sailors
Cylon fiber (PPBO) Poly (p-phenylene-2,6-benzobisoxazole)
Zylon fibers have extremely good properties. Little stretch and high dimensional stability due to high strength. However, not very UV-resistant, more expensive than aramid, with a shorter lifespan.
Technical data of artificial materials in comparison
Notes on the information in the table:
The unit g / den means grams per denier . A 1-denier polyester fiber has a diameter of approximately 10 micrometers (0.01 mm).
Elasticity value: A higher numerical value means a lower elasticity. Sails with low elasticity have the advantage that they keep their shape even under high loads.
UV resistance: After the specified number of months, the breaking load has been reduced to half of the new value (applies to subtropical waters, for example the Mediterranean).
Loss of buckling: The percentage is the loss of breaking load after 60 buckling movements.
| material | Elasticity value | Breaking load | UV resistance | Kink loss |
|---|---|---|---|---|
| polyamide | 45 g / den | 9.5 g / den | 3-4 months | 0% |
| polyester | 80-120 g / den | 8 g / den | over 7 months | 0% |
| Polyethylene naphthalate (PEN) | 250 g / den | 10 g / den | 6 months | 4% |
| Polyester high strength | 510 g / den | 23 g / den | 1-2 months | 15% |
| Aramid | 540 g / den | 28 g / den | 3-4 months | 7% |
| Standard aramid | 600 g / den | 23 g / den | 2-3 months | 25% |
| High modulus aramid | 940 g / den | 24 g / den | 2-3 months | 27% |
| High strength polyethylene | 1250 g / den | 33 g / den | 6-7 months | 0% |
| Carbon fiber, carbon | 1200-2400 g / den | 20-40 g / den | no influence | 30-100% |
Source: specialist magazine Yachtrevue , issue 4/2006
Sail cuts
Sails are made from a more or less large number of strips of cloth, the so-called sail tracks. Depending on the shape of these sail tracks and the corresponding course of the seams with which they are held together, we speak of different sail cuts. The sail cut has an impact on the durability and performance of the sail.
Sails should be as dimensionally stable as possible under high loads. The stretch (stretchability) of the canvas has a significant influence on the dimensional stability . The horizontal bar should be as small as possible. Polyester fabrics, for example, have a low stretch in the warp and weft direction (in the direction of the longitudinal and transverse threads), but the diagonal is large. We try to take this fact into account by means of various cuts so that the fabric is not loaded diagonally when sailing.
The horizontal cut or cross cut is the most popular and most tried and tested sail cut on mainsails. With this cut, the seams run roughly parallel, at right angles to the tendon of the leech, and in square sails at right angles to the rahliek. This cut is inexpensive to manufacture, robust to use and generally the most durable.
The flap cut is a sail cut that is often used for fore or stay sails (jib). A diagonal seam, called a lashing, runs from the clew, in the direction of the sheet pull, to the luff of the sail. From the lashing, the panels run approximately perpendicular to the leech and leech.
With a radial cut (tri or full radial cut ), the seams run in a star shape approximately from the middle of the lower third of the sail to the three corners of the sail or in a radial pattern away from them. This cut is mainly used for headsails, as the force is introduced into the sail with the clew in a diagonal direction.
Horizontal section
Biradial cut
Full or tri-radial cut
Aerodynamics of the sail
The construction of sails is determined by the laws of aerodynamics . They are aeroelastic wings .
When the wind blows against it, the sail takes on a curved shape ( belly ) and develops a force that is proportional to the product of the sail area and the square of the wind speed . The force acts perpendicular to the surface of the sail in the leeward direction . In addition to the shape and size of the sail and the wind speed, the angle of attack of the wind on the sail also has an influence on the magnitude of the force . Depending on the angle of attack, either the component propulsion by resistance or the component propulsion by buoyancy predominates .
Propulsion by resistance
Resistance propulsion creates a force on the sail when it slows down or interrupts the air flow. The size of the force depends on the size of the sail area and its drag coefficient (c w value). The drag coefficient is greatest when the sail has the shape of a hollow hemisphere (c w value ≈ 1.4). That is why special sails for downwind courses , such as spinnakers , are very bulbous and have a large sail area.
Propulsion by dynamic lift (wing effect)
If sails are flown against at a certain angle ( angle of attack about 5 ° to 30 °), they work according to the same principles as the wing of an airplane or the wing of a hang glider . If the angle of attack increases, the flow breaks off and the propulsion through resistance predominates (see above).
The air stroking along the sail creates a force that acts on the first third and is essentially perpendicular to the cloth. It is the result of different aerodynamic processes:
According to Newton's third law (force = counterforce), the deflection of the air flow on the windward side of the sail creates a force on the sail. The magnitude of this force corresponds to the change in momentum of the air mass deflected by the sail per unit of time (see simplified sketch on the right).
The leeward side of the sail very effectively accelerates the neighboring air backwards. When the accelerated air on the leeward side merges with the less accelerated air on the windward side of the sail after it has flown around the sail, the flow is deflected with a vectorial acceleration component perpendicular to the sail towards windward. This results in an equally large counterforce on the sail in the lee direction, based on Newton's third law.
If the air flow around the sail is examined in detail, it can be seen that the air flows faster on the leeward side of the sail than on the windward side . According to the Bernoulli effect, this leads to increased pressure on the windward side and reduced pressure on the leeward side of the sail. This pressure difference also explains the force on the sail.
When sails are arranged close together, they can influence each other positively. One example is the elongated nozzle that forms in the space between the foresail and the mainsail when slump rigging. Due to the Venturi effect, there is a higher flow velocity in this nozzle than in the surrounding area. This creates additional buoyancy on the mainsail. However, the view that there is a jet effect between the fore and mainsail is controversial.
Areas of application of sails
A large part of the sails manufactured today is used on sailing ships , sailing yachts and sailing boats . But special sails are also used for windsurfing , ice and sand sailing . Since these vehicles reach very high speeds on certain courses , the sails have to be cut very flat (with little belly) for aerodynamic reasons.
literature
- Czeslaw A. Marchaj: The aerodynamics of the sails. Theory and practice. Delius Klasing, Bielefeld 2001, ISBN 3-7688-1017-8 .
- Nicolas Bessert: Unsteady aeroelastic calculation of yacht sails . Shaker Verlag , 1999, ISBN 3-8265-6630-0 .
Web links
- Sail care tips ( memento from February 27, 2009 in the Internet Archive ) from North-Sails
Individual evidence
- ↑ Duden, German Universal Dictionary, 8th edition (2015)
- ↑ Heinz Overschmidt: Driving license A for sailors. Verlag Delius, Klasing & Co, Bielefeld / Berlin 1973, ISBN 3-7688-0071-7 , p. 49 ff.
- ^ Lionel Casson : Ships and Seamanship in the Ancient World. Johns Hopkins University Press, 1995, ISBN 0-8018-5130-0 , pp. 243-245.
- ^ Lionel Casson: Ships and Seamanship in the Ancient World. Johns Hopkins University Press, 1995, ISBN 0-8018-5130-0 , pp. 243-245.
- ^ Lionel Casson: The Sails of the Ancient Mariner. In: Archeology. Volume 7, No. 4, 1954, pp. 214-219.
- ↑ Lynn White: The Diffusion of the Lateen Sail. Medieval Religion and Technology. Collected Essays, University of California Press, 1978, ISBN 0-520-03566-6 , p. 255.
- ↑ IC Campbell: The Lateen Sail in World History. ( Memento of the original from August 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 192 kB). In: Journal of World History. Volume 6, No. 1, 1995, pp. 8-11.
- ↑ George Makris: Ships. In: Angeliki E. Laiou (Ed.): The Economic History of Byzantium. From the Seventh through the Fifteenth Century. Volume 1, Dumbarton Oaks 2002, ISBN 0-88402-288-9 , p. 96.
- ↑ Zaraza Friedman, Levent Zoroğlu: Kelenderis Ship Square or Lateen Sail? In: The International Journal of Nautical Archeology. Volume 35, No. 1, 2006, pp. 113-114.
- ^ John H. Pryor, Elizabeth M. Jeffreys: The Age of the ΔΡΟΜΩΝ. The Byzantine Navy approx. 500–1204. (= The Medieval Mediterranean. Peoples, Economies and Cultures, 400-1500. Volume 62). Brill Academic Publishers, 2006, ISBN 90-04-15197-4 , pp. 153-161.
- ^ F. Castro, N. Fonseca, T. Vacas, F. Ciciliot: A Quantitative Look at Mediterranean Lateen- and Square-Rigged Ships. (Part 1). In: The International Journal of Nautical Archeology. Volume 37, No. 2, 2008, pp. 347-359.
- ^ Julian Whitewright: The Mediterranean Lateen Sail in Late Antiquity. In: The International Journal of Nautical Archeology. Volume 38, No. 1, 2009, pp. 97-104.
- ↑ a b on- board manual (PDF; 2.3 MB) of Roald Amundsen . 3rd edition, p. 16.
- ↑ SSS Schonerbrigg (PDF; 1.0 MB) Greif , sail folder, p. 12.
- ↑ Anil N. Netravali, Christopher M. Pastore: Sustainable Composites: Fibers, Resins and Applications. DEStech Publications, 2014, ISBN 978-1-60595-111-9 , p. 165.
- ^ Jenny Bennett: Sailing into the Past: Learning from Replica Ships. Seaforth Publishing, 2009, ISBN 978-1-84832-013-0 , p. 184.
- ↑ Joachim Schult: Segler-Lexikon. 13th edition. Delius Klasing, Bielefeld 2008, ISBN 978-3-87412-103-3 , p. 132, with illustration.
- ^ Sails / Aerodynamics ( Memento from September 7, 2011 in the Internet Archive ).
