Fibers Used in Sails at Ullman Sails.Thu, 19th Feb 2009
By Chuck Skewes
The fibers used in sails today are a far cry from the ones used in the past. Here is a brief guide of these fibers and the characteristics of each one as well as their best use.
Polyester: (DuPonts trade name is Dacron) 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 A proven fiber for durability, polyester has been replaced by higher modulus fibers for most racing applications.
Kevlar: A gold colores 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.
Twaron: Made by the German company Akzo, Twaron is an Aramid product very similar to Kevlar.
Technora: Made by the Japanese company Teijin, Technora is an Aramid developed as 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.
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 designers 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.
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.
Dyneema: Produced by the Dutch company DSM, Dyneema, like Spectra is a highly processed polyethylene which offers good UV resistance, very high theoretical initial modulus and super breaking strength. It also shares Spectra's creep characteristics.
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.
This article was posted on Thu, 19th Feb 2009