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.
ch2weave150.gif (2097 bytes) 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.
Laminates
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 on the following page.
The advantage laminates have over woven cloth is that the Mylar film reinforces in all directions. Mylar has strength 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 patented Tape-Drive® construction system. Your UK Sailmaker will be happy to discuss sailcloth for your boat in detail.
Sailcloth Yarns
Grand Prix racers turn to PBO Zylon — PBO for short. The modulus of PBO is so great that it makes any aramid yarns like Kevlar look stretchy. The material is extremely expensive and it breaks down faster than Kevlar® when exposed to light. To shield it from harmful light, cloth manufacturers are protecting the yarns with dyed mylar. Dimension/Polyant for example uses a product called Magna Shield which is copper colored. Instead of using laminated with PBO, UK Sailmakers uses this yarn more efficiently as Tape-Drive® tape only. That way its super strength is used to carry the sail's primary loads.
Kevlar, Technora and Twaron are trademarks for aramid yarns which are the most common high-tech yarn used in performance sailmaking. Dupont's trademarked aramids are called Kevlar® and Kevlar® Edge™. Aramids have a distinctive brownish yellow color. Aramids have a couple of drawbacks; they lose strength from flogging as well as from exposure to the sun's ultraviolet rays.
Technora Black, an aramid made by Teijin in Japan, is a material we have been making sails with for the last five years, with outstanding results. Customers love its durability. Recently Dupont introduced Kevlar® Edge™ yarn that has slightly better modulus to Kevlar® 49 and 25% more tenacity than Kevlar® 49. That means this yarn will have the durability of Technora and the same shape holding ability as Kevlar® 49. See the chart below..
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 more expensive than Kevlar® . Other sailmakers have problems working with Spectra because it elongates after staying under high loads. Used as a skin fabric in UK's Tape-Drive® construction system, the Spectra fabric never becomes loaded enough to elongate.
Another new yarn is made of PEN fibers (Polyethylene Napthalate). It is most commonly sold under Challenge Sailcloth's tradename Pentex. Stan-dard Polyester (Dacron) is short for polyethylene terepthalate or PET. PEN fibers have the identical initial breaking strength as PET yarns, but PEN fibers have 2.5 times less stretch than polyester yarns. Tape-Drive® tapes and laminates made with PEN fibers greatly improve the performance of our budget-priced Tape-Drive® sails.