Sailcloth
Sailcloth is cloth used to make sails. It can be made of a variety of materials, including natural fibers such as flax, hemp, or cotton in various forms of sail canvas, and synthetic fibers such as nylon, polyester, aramids, and carbon fibers in various woven, spun, and molded textiles.
History
Western traditions
used wool for sailcloth. The cloth was woven in one of three ways, according to locality and tradition: plain weave with individual threads going over and under each other, three-shaft twill with two threads going over and under at each cross thread, and four-shaft twill with thread interwoven with two threads at a time in either direction. Such was the practice from the 11th through the 14th centuries.Doek is Dutch for cloth, which evolved into the English word "duck" in reference to sail canvas. Duck was typically made from cotton or linen, with some use of hemp. These natural fibers have poor resistance to rot, UV light and water absorption. Linen is stronger, but cotton is lighter. Linen was the traditional fiber of sails until it was supplanted by cotton during the 19th century. 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. As sail size grew linen was too heavy to be practical so cotton became more popular. 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. It was not until the late 20th century that natural fibers were replaced by synthetics in mainstream use. Cotton sailcloth is still used for sportswear, upholstery and draperies. The traditional width for carded cotton sailcloth in the US was 23 inches while the British standard was 24 inches.
Austronesian traditions
In the ancient seafaring traditions of the Austronesian peoples of the Indo-Pacific, the sails were traditionally made from woven panels of pandan leaves and lashed with ropes usually made from coconut coir. These sails were integral in the subsequent migrations of the Austronesians from Taiwan, to Island Southeast Asia, Micronesia, Island Melanesia, Polynesia, and Madagascar. Some examples of pandan mat sails were so finely woven that they were compared to "coarse linen" by the Spanish and "dressed sheepskin" by the Dutch.Specific examples of sails made from pandan mats in Austronesian-speaking regions include the sails of the fayang rafts of the Amis people in Taiwan, the various bangka of the Philippines, the kabang of the Moken people, the wa of the Caroline Islands and Yap, the tepukei of the Taumako Islands, the oblong sails of the canoes of the Ninigo Islands, the baurua of the Gilbert Islands, the drua of Fiji, and the waʻa kaulua of Hawaiʻi, among others. The technology of pandan mat sails were also introduced to non-Austronesian peoples via contact, like to the Yolngu of Australia.
Sails could also be made from woven mats of other similar plant leaves and fibers, including those from sugar palms, buri palms, and nipa palms.
Modern fibers
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. The following sections discuss the attributes of fibers assuming a good design and careful construction. According to Mahr, there are six key factors in evaluating a fiber for suitability in weaving a sail-cloth:- Initial modulus – The ability to resist stretching. Higher resistance is better for upwind sails.
- Breaking strength – Measured as a force per cross sectional area of fiber. Higher is better for sails.
- Creep – Describes the long term stretch of a fiber or fabric. A material with creep may have a superior modulus, but lose its shape over time.
- Resistance to ultraviolet light – Strength loss from exposure to the Sun’s UV rays measured by a standardized exposure test.
- Flex strength – Strength lost due to bending, folding, or flogging, which is frequently measured with an industry standard 50 fold test.
- Cost-effectiveness –Both the initial cost and its durability of the material define its cost-effectiveness over time.
Nylon
is used in spinnakers because of its light weight, high tensile strength, superior abrasion resistance and flexibility. However, it has a low modulus allowing too much stretch to be suitable for upwind sails. Nylon is more susceptible to UV and chemical degradation than polyesters and its physical properties can change due to moisture absorption.Polyester (PET)
, 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. PET has excellent resiliency, high abrasion resistance, high UV resistance, high flex strength and low cost. Low absorbency allows the fiber to dry quickly. 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. Dacron is the brand name of Dupont’s Type 52 high modulus fiber made specifically for sailcloth. Allied Signal has produced a fiber called 1W70 polyester that has a 27% higher tenacity than Dacron. Other trade names include Terylene, Tetoron, Trevira and Diolen.PEN fiber (Pentex)
PEN, 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. 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. 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, or as a taffeta outer layer of a laminate, protecting a PET film. 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. 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. 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. 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.Kevlar, along with other aramid fibers, have poor UV resistance and rapid loss of strength with flexing, folding and flogging. Minimal flogging and careful handling can greatly extend the life of a Kevlar sail.