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post #1 of Old 06-03-2004 Thread Starter
Brian Hancock
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It All Starts with a Yarn

Understanding a little bit about sailcloth options will help you when it comes to making your next sail purchase.
What is sailcloth, that magical material that's woven, plied, and laminated together to build better sails? Is it complex science and chemistry, or is it just a mystery?

If you have been wondering what it's all about, why there are those differently colored sails and funky panel layouts, stay tuned to this slot for the next few months while we untangle the weave and present you with a comprehensive look at fabrics, panel layouts, sails, and sail trim. By way of this series of articles devised to educate you, the cruising sailor, we hope to enable you to make better, more informed choices the next time you are out shopping for sails.

It all starts with a yarn, or more to the point, thousands of yarns. Space-age fibers, some with names longer than the length of your boat, form the basis of all fabrics, and it's in their make-up and lay-up that sailcloth is created.

When you see new names like VectranTM and CertranTM, PBO and PEN listed as fabric options for your sails, it's easy to be intimidated and long for the dull days of DacronTM. Just remember that all these yarns were created for industrial and defense use and that the sailing industry became a subsequent beneficiary of all this technology. Sailmakers and fabric makers would never have had the resources to "invent" a fiber that everyone wants, despite the fact that it's prohibitively expensive, doesn't last long, and will soon have to be replaced. It's an industry's dream come true.

Whether you're talking about spinnakers or working sails, yarns are the basic common denominators.
Creating great sailcloth is a unique process involving engineering, design, and what I like to call sex appeal. Once the fabric has been created, then it's up to the sailmaker to use it to its best advantage to create your sails.

In an industry that turns out MylarTM marvels and DacronTM wonders, it's easy to see where you can get confused about what's best for your boat. Let's start at the very beginning and look at how fabric is created.

A great sailcloth is the sum of its parts. In woven fabrics like Dacron and NylonTM, the components are the yarn, the weave, and the finish. In a laminate, it's the yarn, the film, the adhesive, and the amount of pressure brought to bear on the fabric during lamination that hold it all together. The most important component is still the yarn, and since this is the area where the most development and change occurs, let's look at the available yarns and their distinctive features.

Let's take VectranTM for an example. This fine filament was created for the defense industry. The military-industrial complex was looking for a fiber that could be used to tow listening devices behind submarines. The listening device was paid out behind the sub to an exact distance. The noise of the sub's engines were then tuned out so that the device could listen for other noises. The length of the tow had to remain constant, and the fiber had to withstand adverse conditions. VectranTM was the result, and it seemed to be an ideal fiber for use in sailcloth, until its creators brought it to the surface and found that sunlight was its greatest enemy.

Exotic fibers and laminates are always in evidence at grand prix regattas like Key West Race Week.
Before assessing the benefits of each fiber, it's important to take into account not only their relative stretch characteristics, but also their weaknesses. While many of the fibers mentioned here are not suitable for cruising sails, it's interesting to look at them if only to compare. A good example is Carbon. This material has an unbelievable resistance to stretch; however, it is brittle and fragile, and does not like to be bent or flogged—hardly a suitable fiber for cruisers, although deep-pocketed racers can't get enough of it. Durable Dupont DacronTM and Allied-Signal's(now called Honeywell) PentexTM are both Polyester yarns at opposite ends of the performance spectrum. If you've owned a boat since DacronTM was first introduced in the '50s, you have owned a DacronTM sail. This fiber became a benchmark, and remained so because of its durability, relatively inexpensive price tag, and ease of use for sailmakers to make into sails. Its only drawback was that it stretched, and stretchy fabric distorts sail shape over time. Almost half a century later along comes PentexTM, or PEN as it's known in the trade. PEN is an acronym for "polyethylene napthalate" and is a super-DacronTM combining all the great qualities of DacronTM without the one major drawback—stretch.

PentexTM was developed for the tire and mechanical rubber markets and has several features that make it well suited for sailcloth applications. Aside from being rugged, it has two and a half times the modulus, or stretch resistance, of regular DacronTM. This translates into two and a half times less stretch for cruising sails of equal weight. PentexTM is best used in a laminate form, and has been used with equal success in one-design jibs and mega-yacht mainsails.

"The most successful fibers available for sailmaking have been the aramids, the most recognizable of which is Kevlar."
SpectraTM, DyneemaTM, and CertranTM are close cousins, made by different manufacturers. All these fibers are polyethylene, the most recognizable of which is SpectraTM made by Honeywell. DyneemaTM is made in Holland by the Dutch company DSM, while CertranTM is made in the US by Hoechst Celanese. All three fibers have excellent durability. They don't mind sunlight, flexing or chafe and have an outstanding resistance to stretch. What's the problem then? Their initial stretch resistance is great; however, over time they start to "creep." In other words, they stretch permanently, and this distortion is bad for sail shape. Add to that the difficulties with laminating because of their slippery texture and the problems that occur because the fibers melt at a relatively low temperature, and you end up with a wonderful thread, but less-than-perfect fabric. The most successful fibers available for sailmaking have been the aramids, the most recognizable of which is Kevlar. Its distinctive gold hue has become a standard on racing boats. Like SpectraTM, Kevlar also has its drawbacks—it is adversely affected by sunlight and flutter, two major ingredients of most sailing days.

Fortunately the threads are only part of the equation, and some of their weakness can be masked by the clever use of UV inhibitors. You can trust sailcloth makers not to give up on a wonder fiber, and instead figure out how to incorporate the yarns into the overall makeup of the cloth while minimizing the fragility of the fiber. One of the most effective ways to do this is to sandwich the yarns between UV protective film, which brings us to the second most important component of sailcloth—the film.

When not delving into the world of sailcloth, the author spends time aboard his 50-footer, Great Circle, above.
A good film is the substrate upon which most fine racing fabrics are founded, but it too has not been without problems. The most common film used in sailcloth is MylarTM, which is extruded from polyester and comes in different thicknesses, depending upon its application. Other than providing sex appeal, the film allows fibers to be laid in a multitude of directions where they can be most effective. The problem with MylarTM is the opposite of polyester. In its original form, polyester stretches. Once extruded into film, MylarTM shrinks, and in doing so distorts the shape of the sail. Sailcloth makers still rely on the film to aid in minimizing off-threadline stretch, and now they rely on it to protect delicate yarns from sunlight and abrasion, as well as to cushion flexing.

With new wonder yarns, super adhesives, and high-tech treated films, cloth manufacturers have the scientific side of sailcloth fairly well sorted out. It's now up to their artistic and creative engineering abilities to combine all these components into a sailcloth from which sailmakers can fashion a sail. 

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