Sailcloth
Scrim is a loose weave or lattice of strands, typically bonded where they cross to maintain the grid pattern. PEN laminates are an economical alternative for higher performance sail. Kevlar, an aramid fiber, has become the predominant fiber for racing sails, since it was introduced by DuPont in 1971.Low absorbency allows the fiber to dry quickly. Just as PEN fiber is stronger than PET fiber, PEN film is stronger than PET film.
The quality and weight of the weave can be more critical than the choice of fibers, since a poor weave can lead to high stretch and poor sail form. Dacron is the brand name of Dupont’s Type 52 high modulus fiber made specifically for sailcloth.
Lamination also allow fibers to be placed in a straight, uninterrupted paths. There are four main construction styles: Film is sandwiched in between two layers of woven taffeta, the film provides most of the stretch resistance and the taffeta enhances tear and abrasion resistance.
There are two popular types of Kevlar: Type 29 and Type 49, the latter having a 50% higher initial modulus than Type 29 but a lower flex loss. Linen is stronger, but cotton is lighter.
Among PBO’s desirable properties are high thermal stability, low creep, high chemical resistance, high cut and abrasion resistance, and excellent resistance to stretch after repeated folding. Twaron SM is similar to Kevlar 29.
cloth . PET has been replaced by stronger fibers for most serious racing applications, but remains the most popular sail cloth due to lower price and high durability.
Because it only shrinks about a third as much as a good PET, PEN can not be woven as tightly; thus, woven PEN must be impregnated with resin making sails prone to damage from improper use and handling. In some cases UV protection is added. Woven fabric with high UV and abrasion protection is added to the Film-on-Film.
Unbalanced means a heavier yarn is used in one direction. This allows greater loads to radiate up from the clew (back lower corner) along the leech (back edge).
There are six key factors in evaluating a fiber for suitability in weaving a sail-cloth: There is no perfect solution since in most cases the increase of one attribute generally results in the decreased attractiveness of another. As load is applied the yarns attempt to straighten out, this results in the fabric stretching, commonly referred to as ‘crimp”.
The UV endurance is inferior to PET and PEN, but the degradation levels off after roughly 400 hours of exposure, while the Aramids and Spectra continue to degrade. Carbon fiber is a high modulus synthetic fiber made from carbon atoms. These natural fibers have poor resistance to rot, UV light and water absorption.
The traditional width for carded cotton sailcloth in the US was 23 inches (58 cm) while the British standard was 24 inches (61 cm). The characteristics of a sail are due to design, construction and the attributes of the fibers, which are woven together to make the sail cloth. Reduced stretch generally also reduces the flexibility causing a trade-off of performance for durability.
However, it also exhibits permanent and continuous elongation under a sustained load (AKA: creep). PET has excellent resiliency, high abrasion resistance, high UV resistance, high flex strength and low cost.
Additional advantages of Vectran fiber include zero creep, high chemical and abrasion resistance and high tensile strength. Cotton did not substantially replace linen worldwide until the end of the age of sail; however, in some cases the strength of linen was preferred for some types of sails.
Other trade names include Terylene, Tetoron, Trevira and Diolen. PEN (Polyethylene naphthalate)commonly known by Honeywell s trade name Pentex , is another kind of polyester fiber, which stretches only 40% as much as standard PET fibers, but about twice as much as Kevlar 29. But PBO’s has poor resistance to both UV and visible light. Vectran is a polyester-based high performance LCP (liquid crystal polymer) produced by Ticona.
Linen was the traditional fiber of sails until it was supplanted by cotton during the 19th century. In high quality cloth, the strands or scrim are tensioned during the lamination process. The drawbacks are: film is not as abrasion or flex resistant as a weave, it does not protect the structural fibers from UV rays.
It is a gold fiber with an initial modulus that is significantly higher than other high modulus yarns, including aramids. It is stronger, has a higher strength to weight ratio than steel, and has a modulus that is five times greater than PET, and about twice as high as PEN.
Most moderns sails are “crosscut”, which is an unbalanced technique where the heavier yarns is in the fill. This technique is more experimental than practical, but may yield results in time. .
It is naturally gold in color and has a modulus similar to Kevlar 29, but has less strength loss with flex. In the US and Britain, the most well-known trade names are Mylar and Melinex. PEN film is extruded and biaxially oriented version of PEN fiber.
This is an attractive method to combine high modulus fibers with poor UV resistance. Wovens on both sides of a scrim without the film layer. It is often used by European sailcloth manufacturers, is available in a wider variety of yarn sizes than Spectra, and is growing in popularity in North America. Hoechst Celanese produces Certran polyethylene similar to Spectra, with about one half the modulus rating of Spectra.
Because of this Spectra is only used in spinnakers on high performance boats where the sails are replaced regularly. Equivalent to Spectra, Dyneema is produced by the Dutch company DSM. Laminating film to film around the strands creates a very strong and dependable bond reducing the amount of adhesive needed.
In some newer styles, off threadline aramid yarns, are also laid into the laminate. As sail size grew linen was too heavy to be practical so cotton became more popular.
PBO is also quite flexible and has a soft feel. At first cotton was used as a matter of necessity in the United States as it was indigenous and the supply of flax was periodically interrupted by wars such as the War of 1812, during which demand for sailcloth for military use was high.
Like Kevlar, the fiber is a bright gold color. Spectra is an ultra high molecular weight polyethylene (UHMWPE) made by Honeywell, which offers superior UV resistance (on par with PET), very high initial modulus numbers (second only to high modulus Carbon Fiber), superior breaking strength, and high flex strength. It is an extruded and biaxially oriented version of PET fiber.
Allied Signal has produced a fiber called 1W70 polyester that has a 27% higher tenacity than Dacron. It is virtually unaffected by UV exposure and provides exceptionally low stretch.
DuPont has developed higher modulus Types 129, 149 and 159, but these have seen little use in sails, since generally as the modulus increases the flex strength decreases. DuPont has recently introduced Kevlar Edge, a fiber developed specifically for sails with 25% higher flex strength and a higher modulus than Kevlar 49.
Strands and scrims are used to strengthen or reinforce sailcloth (see laminates below). In the 1970s sailmakers began to laminate multiple materials with different characteristics to synergize the qualities of each. This is a benefit in endurance applications and for cruising sails where durability is key.
Solving both problems generally sends the price out of range for most sailors. Nylon is used in spinnakers because of its light weight, high tensile strength, superior abrasion resistance and flexibility. The yarns in balanced cloth are the same diameter and weight in lengthwise (the “warp”) and across the width of the cloth (the “fill”).
Nylon is more susceptible to UV and chemical degradation than polyesters and its physical properties can change due to moisture absorption. Polyethylene terephthalate, the most common type of polyester, is the most common fiber used in sailcloth; it is also commonly referred to by the brand name Dacron. Cotton sailcloth is still used for sportswear, upholstery and draperies.
However, it has a low modulus allowing too much stretch to be suitable for upwind sails. Typically sails were made from flax (linen), hemp or cotton in various forms including canvas.
Duck was typically made from cotton or linen (flax), with some use of hemp. Sails have been made from cloth for all of recorded history.
This is especially true of mainsails and high aspect jibs. Woven sail cloths have an inherent problem with stretch resistance. The following sections discuss the attributes of fibers assuming a good design and careful construction.
Most sails are made from synthetic fibers ranging from low-cost nylon or polyester to expensive aramids or carbon fibers. Thus load-bearing members are laid straight, which maximizes the high modulus of the fibers, where a woven material will have some inherent stretch to the weave.
Ironically, fibers which are resistant to stretching, can not be woven as tightly as more flexible fibers such as PET, thus the cloth is more affected by crimp. Films are thin sheet material extruded from synthetic polymers and are typically used along with woven cloth in a laminate (see laminates below). PET film is the most common film used in laminated sailcloth. It has similar properties to Spectra including superior resistance to flex fatigue and UV degradation but also exhibits creep. PBO (Poly (p-phenylene-2, 6-benzobisoxazole)) is liquid crystal polymer developed by Japan-based Toyobo under the trade name Zylon.
The high-end versions of this method use a woven Spectra or Kevlar taffeta. This combines the best of the above, but is costly, heavy, and stiff.
Weight is described in ounces, for example an 8 oz. However, PEN film is rarely used in standard sailcloth styles because it shrinks more rapidly than PET, is less resistant to abuse, and reduces the working life of the sail. Strands are combined from fibers; these are frequently narrow flat bands or ribbons of high strength material.
In some cases the second layer of taffeta is eliminated for cost and weight savings In this construction, a scrim or strands (inserts) are sandwiched between layers of film. Twaron HM (High modulus) has similar stretch properties to Kevlar 49, greater tensile strength and better UV resistance.
The problem is getting enough high modulus yarn into the sandwich, and still being able to get a good bond, because, dissimilar fabrics don’t often bond well. This means that an area of 28.5 inches x 36 inches weighs 8 ounces. Sailcloth is woven in two forms: balanced and unbalanced.
Kevlar, along with other aramid fibers, have poor UV resistance (Kevlar loses strength roughly twice as quickly in sunlight as PET) and rapid loss of strength with flexing, folding and flogging. However, modern sails are rarely made from natural fibers.
PEN is better suited for making laminated sailcloth, where the fibers are laid straight for strength and are bonded to sheets of film for stability (e.g., PET film often called by one of its trade names Mylar), or as a taffeta outer layer of a laminate, protecting a PET film. Recent strides in technology now offer many options for the sailmaker. Doek is Dutch for cloth, which was evolved into the English word “duck” in reference to sail canvas.
Using sheets of PET or PEN reduces stretch in all directions, where weaves are most efficient in the direction of the threadlines. Minimal flogging and careful handling can greatly extend the life of a Kevlar sail. Technora is an aramid, which is produced in Japan by Teijin, has a slightly lower modulus strength than Kevlar 29 but a slightly higher resistance to flex fatigue.
In a weave the warp and fill yarns pass over and under one another. Variants can balance along a continuum from brittle with no-stretch to extreme durability/flexibility with only slightly more stretch than aramid sails. Combed singles yarn sailcloth in high counts is used for spinnaker and head sails.
Technora is most often used as bias support (X-ply) in laminate sailcloth. Twaron is an aramid, which is produced in The Netherlands by Teijin, is chemically and physically similar to DuPont’s Kevlar. This results in a change in shape as the sail ages.
The fiber’s lower UV resistance is enhanced by dying the naturally gold fiber black. It was not until the late 20th century that natural fibers were replaced by synthetics in mainstream use.
The count often is 148 by 160 and the fabric is finished at 40 inches (102 cm) wide with a weight of about 6.5 yds./lb (13.10 m/kg).
