Sail trim

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Sail twist with a kite
Sail twist in strong winds

The term sail trim (often wrong: Segeltrimmung ) denotes the sailing setting the sails and the process of setting. The aim is to adapt the sail position or the sail profile to the wind, course and sea ​​conditions . In the wind, the aim is to achieve the best possible ratio of drag ( F W value ) and propulsion ( F A value ). Before the wind, however, it is important to maximize resistance. In strong winds, a correct trim reduces the heel and thereby increases safety , comfort and the lifespan of the sails by reducing killing . In some cases, trimming devices only attack the sail indirectly by changing the setting of the rig ( mast halyard and mast bending).

Control variables in sail trim

Diagram to illustrate the wind gradient at different wind strengths

The following properties of the sail profile are changed:

Luff angle

In order to enable the flow to be laminar , the leading edge of the sail, the luff, must have as small an angle as possible to the direction of the wind, so a parallel alignment is ideal. This angle can be influenced mainly by the sheet , but also to a small extent by the tension of the luff (e.g. by a Cunningham straightener ). However, due to the mast, this angle does not play a major role in mainsails, just as it does in headsails with a furling system .

Angle of attack

The angle of attack describes the angle that the apparent wind and the imaginary profile chord form between the luff and leech of the sail. For optimal propulsion, it must be selected so that there is a laminar flow on the windward and leeward sides of the sail . The imaginary profile chord only represents the middle angle, which is why care must be taken that the stern part of the sail is not bent so much that it acts as a brake in the sense of air resistance again. Usually the optimal angle of attack is therefore approximately 15 ° (depending on the type of sail used). The angle of attack of a sail is regulated with the help of the sheet or the clew point. Since the angle of the imaginary profile chord in relation to the midship axis is not constant at every height of the sail due to the gradient wind, it is set approximately correctly for every height with the aid of the additional trimming devices. This process is controlled with wind threads. If the angle is set correctly at every height, there is automatically a so-called twist (twisting of the sail profile over the height).

twist

Due to the wind gradient (near the ground due to friction there are lower wind speeds than at the top of the mast, which means that the apparent wind at the head of the sail is more aft than at the sail neck), an optimally trimmed sail does not have the same angle of attack over the entire height, but is twisted. This twist is known as a twist . It is created by the cut of the sails, the tension of the leeches and the wind gradient itself. The extent of the twist must be adjusted in order to achieve an optimal flow. A greater twist is required in strong winds than in weak winds, as the wind gradient increases at higher wind speeds. Increased twist reduces the heeling of a boat by reducing the pressure in the upper part of the sail, which can be used to weather strong winds. Too strong a twist causes the sail pressure point to move leeward in strong winds and the occurrence of forces to windward in the mast top , which can lead to excessive heeling, difficult controllability and a difficult to control roll movement of the boat.

Tread depth

The tread depth (also: bulging ) influences both the maximum achievable propulsion of the sail and the maximum height in the wind that can be run. The more bulky, the greater the propulsion and the smaller the maximum height on the wind. It is not possible to change the profile depth without changing the position of the abdomen (location of the highest profile depth). Increasing the tread depth always causes the abdomen to move aft , which is one of the causes of the loss of maximum height on the wind.

Trim devices

Mainsail

Markings on the mainsail
The schematic drawing shows a large tree (1) which is connected to the mast (2) by means of Lümmel fitting (3). In the mainsail (4) there is a thimble on the clew to which the foot stretcher is attached, which is deflected at the boom jib (6) and guided into a clamp (V-clamp) attached to the underside of the boom. The upper pulley for the main sheet (7) is also attached to the underside of the main boom. Likewise the upper pulley of the boom vang (8), whose lower pulley is attached to the lower end of the mast with a clamp. The Lümmel fitting is mounted so that it can be moved vertically as a whole on a rail running in the mast and can be pulled down around the luff by means of a tackle (9) attached to the Lümmel fitting and the lower end of the mast (counter to the pulling effect of the large fall) To tension the mainsail. In addition, the thimble for the Cunningham straightener can be seen on the luff of the main sail (upper edge of the picture). The Dirk (5) is also attached to the main boom.
The end of a leech line. The white plastic clamp is used to secure the line.
A simple tree vang
In the center of the picture, the traveler rail with sledge and mainsheet running over the entire cockpit can be seen . On the right edge of the picture you can see the backstay tensioner, which is several times squat.
  • Main sheet : The main sheet is used to set the angle of the main boom to the ship's longitudinal axis. It is the most important adjustment option and the only one that is always available, while many of the following options are either not provided at all or only need to be used for competitive sailing, depending on the type of boat. The mainsheet is brought close (and thus the boom is moved to the center of the ship) when sailing close to the wind and the further the course is lowered the more the course is changed according to space. Since considerable forces are applied to the main sheet, it is operated via winches or a multiple pulley .
  • Main halyard and Cunningham straightener (short: Cunningham , also: luff straightener ): With these two devices the tension of the luff can be changed. A higher tension results in a flatter profile, at the same time the sail belly moves forward. The advantage of the Cunningham is that it is easier to use.
  • Moveable gooseneck : on dinghies and small cruisers a height adjustable gooseneck instead of Cunningham is often used. The boom is pressed down on the mast and locked in order to tension the mainsail luff.

  • Foot stretcher: This is a simple line or tackle that runs from the clew of the mainsail to the boom and is used to tension the foot. Higher leech tension leads to a flattening of the profile and to a shift of the abdomen towards the main tree . A disadvantage of the downhaul is that when the trim is bulged, the projected sail area is reduced because the clew moves from the boom towards the mast. This problem can be avoided by using a flat reef .
  • Flat reef : Contrary to its name, the flat reef is not a reefing device, but a trimming device. It is a further development of the foot stretcher that works analogously to the Cunningham stretcher for the luff. When using a flat reef, the clew is firmly attached to the boom, the foot of the specially cut sail is dimensioned so that the profile is trimmed as bulky as possible. A few centimeters (in the direction of the sail head and neck) from the clew an additional thimble is incorporated into the mainsail. A straightener is driven on this thimble, through which the sail can be trimmed flat without reducing the projected sail area. The other effects of the shallow reef are identical to those of the downhaul.
  • Leech trim line (also: Achterliekleine , Jakobsleine or: wrongly leech stretcher ): The leech trim line is a thin line that runs through the hem of the mainsail leech. They can be pushed through to prevent the leech from killing, which increases the lifespan of the sail. The performance improvement is minimal. The leech line has practically no effect on the profile. If the tension is excessive, the leech can tip over to windward, which can severely impair the airflow on the sail.
  • Vang (also: tree down device , boom vang or short: Kicker - sometimes the term Kicker used to distinguish systems which can boost the tree addition of simple Niederholern): Around the Twist to control the sail, the boom means kicking strap down to be pulled. An enforced boom vang reduces the twist, increases the tension on the leech and flattens the profile. The importance of the boom vang for the position of the sails is greatest on open and downwind courses. In the case of small rigs (on dinghies) a tightly enforced boom vang leads to a strengthening of the mast bend ( convex side towards the bow ), which additionally flattens the profile in the lower area and shifts it to the luff. If the vang is used to control this bending, its anchor point on the mast can often be adjusted in height using a rail. The simplest form of the tree vang is a tackle that pulls from an attachment point below the lout fitting on the mast to the large boom. Systems that can also tilt the tree upwards (to reverse the effect of a normal tree vang and to make the dirk superfluous) are often referred to as pipe vang . A distinction is made here:
  1. rigid kickers: a rigid pipe carries the tree. Such simple pipe kickers can be adjusted in length either with the help of sledges on the mast or tree, by means of a thread or by means of a telescopic construction (usually lockable by spring bolts).
  2. Spring-loaded kickers: A spring mechanism is combined with a tackle, which allows rapid, stepless adjustment.
  3. Hydraulic kickers: If the forces involved are very high, or if operation with a small crew is to be made easier, such systems are used on large yachts.
  • Backstay tensioner : The backstay tensioner reinforces the mast bend. In this way he relaxes / opens the leech, flattens the profile, especially in the lower part, and shifts it forward. On boats without a backstay , the same effect can be achieved by changing the rigging tension, the sweep angle or the length of the spreaders (a correction on the water is not possible in this case.) On top rigged boats, the effect on the mast bending is only slightly pronounced.
  • Traveler : The traveler consists of a rail attached transversely to the longitudinal axis of the boat and an adjustable slide attached to it. This slide forms the anchor point for the mainsheet. The twist and the tread depth of the sail can be controlled via the traveler by changing the direction of attack of the sheet. If the traveler sled is leeward, the sheet pulls the boom sharply downwards, the twist and profile depth are reduced and the leech closes. If the sled is facing windward, it is the other way around.
  • Reefing lines : Reefing lines are used to reef the sail, i.e. to reduce the size of the sail when the wind increases. Since too large a sail area in strong winds leads to considerable heel and thus automatically to a reduced effective sail area, both safety on board and speed can be increased again by reefing. In addition, the shape of the hull is optimized for a certain heel angle, and too much heel creates the risk of being shot from the sun . With reefed sails, however, some trimming options are no longer necessary, including the Cunningham straightener and the foot straightener, which - depending on the reefing system - are replaced by the reefing lines. Since there is now enough wind anyway, the optimizations are no longer absolutely necessary.

Headsail (jib and genoa)

Markings on the foresail
A movable jib clevis point on its guardrail
  • Jib sheets : Similar to the mainsail, the position of the sail on the headsail is primarily changed with the sheets. However, the foresail always has two sheets, one on port and one on starboard, whereby only the leeward one is used. Except for small dinghies, the jib sheets are guided over winches so that the forces that arise remain manageable.
  • Jib halyard : Analogous to the mainsail, these devices change the tension of the luff. At higher tension, the profile becomes flatter and moves forward and up. In order to achieve a good position of the foresail, the halyard must be penetrated so tightly that no horizontal folds form. If vertical folds appear, it is too tight.
  • Adjustable haul points : on many yachts the jib or genoa sheet runs over a deflection point that can be moved along the longitudinal axis of the boat. This deflection or pick-up point on the foredeck or side deck can usually be operated from the cockpit with the help of lines . The trimming device controls the twist and the profile depth of the foresail by changing the angle of attack of the jib sheet (analogous to the traveler for the main sheet). Moving towards the bow reduces the twist, closes the leech and increases the tread depth; in the stern direction the effect is the opposite. The tensions of the leech and leech, which should be about the same in medium winds, serve as a guide to the close-hauled course (if there are no wind threads). With modern sail cuts, the leech tension should be slightly higher than that of the leech. Adjusting the hole points in the transept direction is less common, the effect in this case is similar to that of a barber hauler.
  • Barber Hauler (also: Barberholer or (jib) Schotbeiholer ): A close guidance of the jib sheet (the pick-up points are close to the midships line) allows driving higher courses close to the wind and reduces the turning angle. On wide courses, however, a good sails position can no longer be achieved with this sheet guidance and the projected sail area is small. This problem can be avoided by using a jib sheet tackle. The outhaul consists of a folding block that is placed on the jib sheet in front of the haul point (alternatively, a metal ring can be used through which the sheet is passed) and is attached to a line. This line isdeflectedover another block, which is mostly attached to the foot rail of the boat, so that the jib can be extended far by pulling the line tight. If the barber hauler is attached amidships of the actual haul points, the sail can be tighter in order to run more height.
  • Achterliektrimmleine (also: Achterliekleine , often falsely: Achterliekstrecker ): The Fockachterliektrimmleine has the same effects as the Achterliektrimmleine the mainsail.
  • Backstay : In Topp and 15/16 rigged craft is controlled Headstay on the backstay of the slack. Pushing through the tensioner reduces the slack and thus shifts the belly of the jib or genoa forward and flattens the sail profile. With an enforced backstay tensioner, more height can be run on the wind.

Aids to trim sails

Trim disc

A trimming disc provides information on the settings of the trimming devices, taking into account the wind and wave conditions. Trimming disks are available in conventional form made of plastic or cardboard, and recently also in electronic form as a smartphone application.

Clicker

A clicker shows the wind direction of the apparent wind and thus facilitates the correct setting of the angle of attack. Clickers are attached either to the mast top or to the shrouds . Alternatively, wool threads (or something similar) can be attached to the shrouds.

Wind threads and strips of canvas

Wind threads (also trim threads, small threads made of light synthetic fiber or wool) just behind the luff of the jib and mainsail, as well as sail or spinnaker cloth strips on the leech of the sails ( Telltales ) show the course of the air flow on the sail. These indicators are used to control the trim of the sail. If all the wind threads blow horizontally following the course of the sail, the trim is optimal (as an exception, the top sheet of cloth may blow intermittently to leeward in very light winds). A fluttering of the threads or cloth strips indicates turbulence and provides the expert with information on which trimming measures should be initiated. The fluttering of the luff or windward threads on the luff indicates that the angle of attack is too small or too large. If only the upper or lower threads flutter on the luff or canvas strips on the leech, the twist must be adjusted using appropriate trim devices.

Trim tables

Trim tables contain information on the settings of individual trim devices under certain conditions. These are overviews that give the inexperienced a better understanding of the interplay between the institutions. The information is usually imprecise or general, as the exact settings depend on the rig, hull and sails used anyway. Good trim tables take into account the strength of the wind, the course to the wind and the swell, as well as the rig of the boat, since trim devices work differently with different rigging.

Individual evidence

  1. ↑ a b c d e f g h i j Peter Schweer: The optimally trimmed rig . 10th edition. Delius Klasing Verlag, Bielefeld 2006, ISBN 3-87412-101-1 .
  2. ↑ a b c d e f g h Joachim Schult: Segeltechnik . 11th edition. Delius Klasing Verlag, Bielefeld 2004, ISBN 3-87412-140-2 .
  3. ↑ Dr. H. Wozniewski: Engine tuning, yes! But how? , current homepage.
  4. ↑ a b Lester Gilbert: Wind Gradient . . current homepage.
  5. ↑ a b c Jan Kuffel: "Series of trimmings, part 3: Tree vang". In: bowline . No. 1-08, December 21, 2007. PALSTEK Verlag GmbH, Hamburg, ISSN  0936-5877 , pp. 74-83
  6. ↑ a b Jan Kuffel: "Series of trimmings, part 1: backstay tensioner". In: bowline . No. 5-07, August 31, 2007. PALSTEK Verlag GmbH, Hamburg, ISSN  0936-5877 , pp. 62-69.
  7. Jump up ↑ Jan Kuffel: "Series of trimmings, part 2: Traveler". In: bowline . No. 6-07, October 27, 2007. PALSTEK Verlag GmbH, Hamburg, ISSN  0936-5877 , pp. 56-65.
  8. ↑ a b c Jan Kuffel: "Series of trimming instruments, part 4: Hol points". In: bowline . No. 2-08, February 29, 2008. PALSTEK Verlag GmbH, Hamburg, ISSN  0936-5877 , pp. 62-71.
  9. ↑ Harald Schwarzlose: Small yachts . 2nd edition, Delius Klasing Verlag, Bielefeld 1997, ISBN 3-7688-0904-8 .
  10. ↑ Telling Tales ( Memento of the original from September 26, 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. . In: Archive of the web presence of WB-Sails Ltd OY , accessed and received on September 26, 2016 (English). @1@ 2Template: Webachiv / IABot / cdn2.hubspot.net
  11. ↑ Dipl.-Ing. Peter Schweer: Sail trim by a professional . . current homepage.

literature

  • Czesław A. Marchaj: The aerodynamics of sails: theory and practice . Delius Klasing, Bielefeld 1997, ISBN 3-7688-1017-8
  • Peter Hahne: Sail trim in theory and practice . Pietsch Verlag, 5th edition, 2019, ISBN 978-3-613-50894-1

Web links

Commons : Sail trim (category)  - collection of images, videos and audio files
Wiktionary: sailing trim  - explanations of meanings, word origins, synonyms, translations