Sailcloth

The Sailors Guide to Sailcloth

The Language of Sailmaking

There are basically two manufacturing processes used to make sailcloth. Wovens are made by weaving threads over and under each other to produce the sail material. The tighter a sailcloth is woven, the better it will perform. Laminates are layers of film, scrim or taffeta that are glued together under incredibly high pressures to form a composite sail material. Composite fabrics are made from two or more constituent components. A scrim is a grid of relatively large, unwoven, straight yarns,. Scrims have little stretch parallel to the yarns but have no off threadline integrity and are usually sandwiched between other layers of scrim in a composite fabric. A film is an extruded sheet of isotropic plastic such as DuPont's Mylar® polyester film. Film's good properties are low stretch in every direction, contributing to bias stability, zero porosity, and a surface that adheres well to other elements in the laminating process. Film's weaknesses are low tear resistance and a tendency to shrink. Tafetta is a woven substrate that makes up the outside of some laminates. Taffeta is usually made from polyester and adds to the durability and chafe resistance of the laminate.

The ability of a material to resist stretch is called the modulus. Laminates generally have higher modulus than wovens of the same material because the threads are pre tensioned and lie straight inside the laminated film. Since fabric properties, especially stretch, are not isotropic, (that is, they vary with direction), fabric orientations are significant. The orientation across the width of a fabric is called the fill. The orientation along the length of a fabric is the warp . These terms come from the weavers' names for the two directions of thread in the loom. Orientations at a significant angle to the warp and fill, especially 45°, are all called the bias .

TERMS:

TENACITY is the tensile stress at rupture of a being expressed in grams force per denier. Tenacity relates to the breaking strength of fibers, and should not be confused with modulus, which relates more directly with a fiber's ability to resist stretch.

DENIER is the weight in grams of 9000 meters of a given yarn. A higher denier signifies a heavier fiber.

FLEX STRENGTH is the ability of a fiber to retain its strength after being folded back and forth. Flex strength is commonly expressed as loss in breaking strength after flutter testing.

INITIAL MODULUS describes a material's inherent ability to resist stretch. Initial modulus is usually expressed as grams of load per unit of stretch for a certain amount of fiber weight. The higher the initial modulus, the less the fiber will stretch.

UV RESISTANCE measures the effect of sunlight on cloth. UV resistance is usually expressed as the time it would take for a material exposed to sunlight to loose half of its breaking strength.

The Fibers

Dacron®: The DuPont® trade name for man made Polyester fiber. This fiber is the foundation of traditional woven sailcloth. Dacron fibers are also used in cruising laminates and Polyester laminated sailcloth where the use of expensive, low stretch, man made aramid fibers is not necessary.

Polyester: The most common fiber used for both woven sailcloth and laminates. Its properties include good UV and flex resistance, as well as being inexpensive. A proven fiber for durability, polyester has been replaced by higher modulus fibers for most racing applications. Woven Dacron, Polyester laminates and Polyester spinnaker cloth are all products made from this versatile fiber. In the sailmaking industry, "Poly" usually refers to polyester spinnaker cloth. Polyester laminate such as PX or PP-Diax are usually referred to by their trade names.

Nylon: Used to make the traditional woven spinnaker fabric, this material is very light weight, but not very stretch resistant. Nylon is manufactured in weights of .5 oz, 30/20, .75oz., 1.5 oz., and 2oz..

Kevlar®: A gold colored aramid made by DuPont, Kevlar's modulus is five times greater than polyester so it stretches less and sails made from it can be lighter. Of all the high modulus fibers, Kevlar has the most proven track record. It is available in both standard K-29, and high modulus K-49 fibers, with the latter being used more and more for high-end racing applications. Although much stronger than polyester, Kevlar is not as durable in terms of fatigue and UV resistance. It is also more expensive. The original high tech fiber, Kevlar is UV sensitive and it's gold color turns brown as it is effected by sunlight.

Spectra®: A high molecular weight polyethylene, Spectra is a product of the Allied-Signal Corporation. Spectra has the highest modulus of any fiber, except carbon, used in sailcloth but has seen limited application in racing sails because of its creep property, meaning that the fiber will permanently stretch when placed under high constant load. This stretch makes it difficult for sail designer to lock in the shapes they want. As a result, Spectra is viewed more as a performance cruising fiber where its excellent flex, UV and abrasion properties along with its traditional white color are perfect for large cruising boats where cloth strength and durability as well as weight aloft are considerations. Spectra is more expensive than Kevlar.

Technora®: Made by the Japanese company Teijin, Technora is an aramid developed as a reinforcement for drive belt applications. In sailcloth, it is dyed black to help its UV resistance. Technora has a modulus similar to Kevlar, slightly better abrasion resistance and is more expensive than Kevlar. Used alone or in composite laminate constructions, Technora is currently recommended as a durable alternative to sun sensitive Kevlar. Often used as a bias support in composite high modulus laminates.

Certran®: A high modulus polyethylene fiber, similar to Spectra, manufactured by Hoechst Celanese. This fiber shares the same resistance to flex fatigue and UV as Spectra so its applications in sailcloth are limited to secondary fibers and areas which can take advantage of its flex, chafe and UV resistance.

Twaron®: High Modulus Twaron or HMT is a fiber very similar to Kevlar but is made by Akzo Nobel. A PPTA fiber with similar stretch resistance to Kevlar -49, but higher breaking strength. Better UV resistance than Kevlar. Bright gold in color.

Vectran®: A polyester based liquid crystal fiber manufactured by Hoechst Celanese. Vectran has a modulus comparable to Kevlar but due to its molecular composition has better flex and abrasion resistance, although its UV properties are worse. Vectran also does not creep. These characteristics make Vectran an interesting candidate as a performance fiber, although it is more expensive than either Kevlar or Spectra.

Dyneema®: Produced by the Dutch company DSM, Dyneema, like Spectra is a highly processed polyethylene which offers good UV resistance, high theoretical initial modulus and super breaking strength. It also shares Spectra's creep characteristics.

Pentex®: polyethylene napthalate polyester fiber. Two times the stretch resistance of regular Dacron polyester, Pentex offers high modulus alternative for woven Dacrons. Best when used in a laminate form. Has similar tenacity to polyester and slightly better UV resistance. This fiber is developing an impressive track record as a laminate.

Carbon: Carbon fibers have extremely high modulus but are not very durable. This problem was addressed with varying degrees of success with the last America's Cup boats. Crews had to be very careful to avoid hard creases in folding. The next Cup will probably see more development, but high cost and inherent fragility may limit this fiber to only the very best funded racing efforts.

PBO Zylon®: Poly(p-phenylene-2,6-benzobisoxazole)(PBO)is a rigid-rod isotropic crystal polymer. PBO fiber is a new high performance fiber developed by TOYOBO Co., Ltd. (Japan). PBO fiber has superior tensile strength and modulus to Aramid fibers (such as Kevlar, Technora and Twaron). It also has outstanding high flame resistance and thermal stability among organic fibers. PBO fiber, furthermore, shows excellent performance, in such properties as creep, chemical resistance, cut/abrasion resistance, and high temperature abrasion resistance, which far exceed Aramid fibers. PBO fiber's moisture regain is low(0.6%) and it is dimensionally stable against humidity.

PBO fiber is quite flexible and has very soft hand in spite of its extremely high mechanical properties. It can be processed into various product form such as continuous filament, staple fiber, spun yarn, woven and knitted fabrics, chopped fiber and pulp. PBO fiber's excellent mechanical properties will enable the design of high strength and light weight fiber reinforced composites. PBO is used in high performance grand prix racing laminates. A very expensive material, PBO offer high performance and light weight at a premium price.

How a sail performs is directly related to the material from which it is made. The characteristics of fibers (Modulus, Tenacity, Flex Life, UV-resistance, Elongation, Flutter Stability) and how those fibers are incorporated in a laminate or a woven material, influence how the finished cloth will perform. With many fibers and fabrics to choose from and with new products being introduced annually, purchasing the right sail can be a confusing process. We hope this guide helps increase your knowledge of sailmaking and sailmaking materials

Maine Sailing Partners
www.mesailing.com
1-888-788-SAIL