Kevlar is probably the most recognised fabric for sails other than Dacron. This pale gold sailcloth has set the world of competitive yacht racing on fire and also done its fair share to contribute to the expense and frustration of being a sailboat owner, especially at the top end of the sport. Basically, to be competitive at the grand prix level you need Kevlar sails. But while Kevlar's benefits include low stretch and a high strength-to-weight ratio, its drawbacks include a lack of durability and short competitive life. Unfortunately, even the very best Kevlar sails won't last very long. It's a delicate balance between performance gain and prohibitive expense.

Kevlar is a fiber that was created and introduced by Du Pont in 1971 when two research scientists by the names of Stephanie Kwolek and Herbert Blades set out to create an entirely new fiber. Their success has had a lasting impact on not only the sailmaking industry, but the world as a whole. It is stronger

Some fabrics are made from a blend of fibers such as Kevlar and carbon in order to maximize the benefits of each.

than steel for its weight and has a modulus five times greater than polyester. When Kevlar was first introduced to the sailmaking industry there were two types: Kevlar 29 and Kevlar 49. Each had properties that were a trade-off against the other. Specifically, Kevlar 49 had a 50-percent higher modulus than Kevlar 29, but what it gained in stretch resistance it gave up in flexibility. Again, because sails flog and flap in the wind, the ability of a fiber to handle flex is very important. Another important drawback with Kevlar is that it has terrible UV properties. In fact, Kevlar loses its strength roughly twice as quickly as polyester, and as soon as it is exposed to sunlight it loses its attractive gold color and turns a dull brown. As a result, the two main ingredients of a summer's day on the water: wind (which causes flogging) and sunshine (which causes UV degradation), are the two worst enemies of this strong but delicate fiber. Fabric makers have since been able to compensate for some of Kevlar's weaknesses by encapsulating the yarns with rugged taffetas that both protect them from the harmful rays of the sun and dampen the bending moment as the sail flaps in the wind.

Since the debut of Kevlar 29 and Kevlar 49, Du Pont has introduced a number of other Kevlar styles including Kevlar 129, Kevlar 149 and Kevlar 159. While these fibers have terrific stretch resistance, this increase in modulus goes hand-in-hand with even lower flex strength, so that most of these fibers have not been useful for making sails. Basically, it's interesting to know that these kinds of fibers exist, but unless sailmakers and fabric makers can figure out how to overcome their weaknesses they might never enter the sailmaking realm.

Another recent Kevlar style introduced by Du Pont is called Kevlar Edge. This new Kevlar fiber has 25-percent higher strength than Kevlar 49, better modulus, and it continues to hold up well after repeated flexing. It also resists breaking, and because of these attributes it is becoming more widely used in sailmaking.

In the end, minimal flogging, careful handling when bagging the sails, and protection from UV exposure can greatly add to the life of Kevlar sail. Despite its cost and weaknesses, it looks as if Kevlar is here to stay as one of the leading performance fibers.

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