UK Sailmakers' Encyclopedia of Sails
2.1 -Sail Cloth
Until the 1980s, woven polyester (better know as Dacron — Dupont's tradename for their polyester yarn) was the only sailcloth in use. Today's cloths include not only the familiar woven dacrons and woven nylons in various weights and finishes, but laminates using yellow aramids, Black Technora, carbon fiber and Spectra yarns.
More and more sailors are turning to laminated sailcloth because laminates are lighter for their strength than Dacron. Laminates also have superior shape holding ability. As the name implies, laminates all have some cloth or yarns glued to one or more layers of Mylar film. Laminates can be made with any of the yarns listed on the chart above.
The advantage laminates have over woven cloth is that the Mylar film reinforces in all directions. The strength of woven cloth lies in the direction of the yarns only. The Mylar film can vary in thickness from fractions of one mil to three or even four mils. UK Sailmakers works closely with the cloth manufacturers to produce custom laminates that are matched to the X-Drive and Tape-Drive® construction processes. Your UK Sailmaker will be happy to discuss sailcloth for your boat in detail.
Grand Prix racers turn to carbon fiber because the modulus of carbon is so great that it makesaramid yarns like Kevlar look stretchy. Instead of using laminates with carbon which are expensive, UK Sailmakers uses this yarn more efficiently along the load paths of the sail. That way its super strength is used to carry the sail's primary loads, while the laminate material is used to create the three-dimensional shape of the sail.
Kevlar, Technora and Twaron are trademarks for aramid yarns. Dupont's trademarked aramid is called Kevlar®. Aramids have a distinctive brownish yellow color. Technora Black, an aramid made by Teijin in Japan, is a material we have been making sails with for two decades, with outstanding results. Customers love its durability.
Spectra yarns are lighter and more flexible than Kevlar® and Technora. Spectra doesn't break down from folding, is impervious to UV radiation, and gets softer with use. Unfortunately, Spectra is one of the most expensive yarns used in sailmaking . Other sailmakers have problems working with Spectra because it elongates after staying under high loads. Used as a skin fabric in UK's X-Drive® and Tape-Drive® construction processes, the Spectra laminate never becomes loaded enough to elongate.
Woven Polyester or Dacron®
Woven polyester sailcloth is extremely durable and relatively inexpensive. Sailmakers know its performance characteristics well since they have been using it since the mid 1950s. When durability is the primary concern, Dacron is the cloth of choice.
Specific styles of woven polyester are commonly named by weight, such as "6.1 oz. Dacron" or "8.3 oz. Dacron". It should be understood that these designations are names and not necessarily actual weights. There is a considerable variation, both up and down, between the actual weight and the named weight assigned to a particular fabric by the manufacturer. This variation is inherent in the manufacturing process, and is not an attempt at deception. Nevertheless, with these fabrics, the actual weight is a reasonably reliable guide as to both its strength and its cost.
The unit of weight in the United States is ounces per "sailmaker's yard," which is 36" by 28.5". The British use ounces per square yard, and Continental Europe uses grams per square meter. Thus 1 oz. American equals 1.26 oz. British and 42.8 grams per square meter.
Woven polyester can vary from a balanced weave where the yarns have equal strength in both warp and fill directions to an unbal-anced weave whose strength is concentrated in either the warp or fill direction. An unbalanced weave that has more strength in the warp direction is called "Warp-Oriented"
and a weave with more strength in the fill direction is called "Fill-Oriented." Extra strength is created by having stronger or more yarns in the warp or fill direction. Simple cross-cut sails use fill-oriented dacrons because the panels are perpendicular to the leech of the sail.