1 Cross cut
Cross cut sails are usually constructed from panels of cloth that run roughly horizontally across the sail, using woven polyester sailcloth known commonly as Dacron, a trade name for the polyester fibres made by DuPont. Dacron has been around for decades and is the mainstay of sailcloth; the one that most people have.
It’s a traditional woven product made on a loom the same way that fabrics have been woven for hundreds of years. As such, Dacron sailcloth is made up from warp fibres and fill fibres and it is the relative properties of each that help define the characteristics of a particular style of cloth. The relationship between the warp and fill fibres is also important because this determines how well the cloth performs in the ‘bias’ direction – the 45° angle between warp and fill. The loads in a sail are multi-directional so knowing how a particular style of cloth performs in the bias direction will help determine what type of sail it’s best suited to. For example, a low-aspect overlapping furling genoa will need different bias characteristics to a tall, thin high aspect mainsail or blade jib.
In the diagram at the top of the page you can see the warp fibres running upwards and the fill fibres running across. Dacron is much stronger in the fill direction – across the cloth – because the fibres are straight, unlike the crimped warp fibres, which will stretch more readily under load. It’s these fundamental properties that determine the cross-cut nature of the panel orientation; the stronger fill fibres are aligned to accommodate the highest loads in the sail that roughly run in a line between the head and the clew. Put simply, the strongest part of the cloth is coping with the highest loads in the sail with the seams running roughly perpendicular to this.
All Dacrons are not created equal, however. Each of the cloth manufacturers will make a range of cloths for different styles, end uses and budgets. What defines each one is its ability to resist stretch. This comes down to a number of qualities: n The fibre itself – how good, or fine it is. n How densely the fibres are woven
– for example, small fibres woven tightly together will stretch less than larger fibres in a loose weave for a given cloth weight.
n The finish. After a Dacron is woven it’s heat treated to shrink it slightly which pulls the fibres together into a tighter weave before being coated in a resin which stabilises the cloth and ‘glues’ it all together. But beware – it is possible to get poor cloth dressed up to look good simply because of the way it has been finished.
The way in which these factors combine determines the overall characteristics of the cloth. A tighter weave with finer fibres and a higher level of finishing will result in firmer fabrics that stretch less, which in turn are more suited to performance or racing applications. Other fabrics will be constructed in a way to deliberately make them feel softer and more suited to cruising.
Cloth selection matters
Each of the Dacron styles that cloth manufacturers produce have different stretch and performance characteristics. There can even be notable differences in stretch characteristics between different batches of the same cloth.
A reputable sailmaker will inspect the performance graphs for a particular style or batch of cloth to ensure it’s suitable for its end use. Failure to do so can have some nasty consequences. An inappropriate style of cloth can prematurely distort the sail shape, which will affect the boat’s handling and performance. The camber lines in the photo (left) show a sail that is badly misshapen. This is actually a fairly new sail. The excessive distortion is caused by either a poor piece of cloth or a style that is inappropriate to the end-use – an extreme example of the risks associated with buying on price over quality.
So although ‘cross cut’ is the simplest construction style, and Dacron is the least expensive cloth, this type of sail still needs the most attention when it comes to getting it right.
While cross cut sails are usually Dacron, nowadays there’s a range of products which go by the generic name of Vectran. The sailcloth is still woven polyester but with the addition of Vectran – a synthetic, highmodulus (strong) aramid fibre – that runs in the fill direction, giving it extra strength and therefore leading to more stable shapes. Vectran sails have become increasingly popular in the last decade, though are more expensive than plain Dacron.