Voyaging sails ahead

In the fading light of a summer evening off the South African coast, we buzzed the catamaran in a helicopter, hovering just feet above the deck. Spray rising from each bow was being flung 50 feet into the air while the crew hunkered down on deck, holding on for the ride of their lives. Team Adventure was slicing through the water at 30 knots heading for the Southern Ocean. From my vantage point in the chopper I could see the clean twist of the mainsail and smooth sail shape, and, surprisingly, the thought going through my head was, “trickle down does work.”

I was partly responsible for the sail development program on Team Adventure Cam Lewis’ mega-catamaran entry in The Race. My responsibility was fabric, and after an extensive testing program that included all the usual suspects - Kevlar, Spectra, 3DL, and carbon - we decided to build most of the inventory out of Cuben Fiber, a revolutionary fabric manufactured in the Arizona desert. My passion in life is voyaging, and over the years I have pushed and prodded for more exotic fibers to be used in voyaging sails. As I watched Team Adventure plunge from wave crest to trough, I felt sure that one day in the very near future we would be seeing Cuben Fiber sails on some larger voyaging yachts - perhaps even on smaller ones after the fabric becomes more accepted. The technology developed and tested at the extreme “lunatic” fringe would one day trickle down to the average voyaging sailboat. It might be a while yet, but the fabric is so good that despite its cost it will become de rigeuer for those who want the very best.

This article is not only about the top-end fabrics and sails; it is also a look at what’s right for your boat whether you are day sailing off Sausalito or heading for blue water. The choices available are enough to confuse even the well-seasoned sailor. “Why can’t I stick with Dacron?” is a good question that often gets asked. And the answer is simple: you can. Some people prefer products that they know and trust, and Dacron has definitely proven itself over many years and many ocean miles. However, sometimes there is a better product available, and your dilemma then becomes deciding if it is right for you.

Remember that the manufacture of sails and fabric is a combination of science, art, engineering, chemistry, and a little bit of mystery, but at its very basis it starts with a yarn. Many yarns, in fact. A sail is simply a number of yarns orientated by a fabric maker and engineered by a sailmaker to efficiently accept the loads in a sail without stretching. Stretch distorts sail shape, and sail shape is at the core of all good sail design. It’s how these yarns are used that sets a great sail apart from an average one, and with so many available fabric choices it’s no wonder sailors are confused. Is there a simple method one can use to look at the choices and decide what’s right?

Holding its shape

Here is how I approach the problem. If you measure value by how long a sail lasts, Dacron might be the right choice. If you measure value by how long a sail holds its shape, then perhaps something more exotic is better. An investment in fabric and engineering up front pays down the road. It’s the age-old situation: generally, if you spend more money you end up with a better product. In sails it’s no different. As boats get bigger, the loads on the sails increase exponentially. You get to a point at which it becomes more cost effective to upgrade your fabric rather than add layer upon layer of Dacron to achieve the same strength and stretch resistance. Half the expense of making a sail is fabric; the other half is labor. When you start using an inordinate amount of fabric to handle loads, your costs rise accordingly. To help you decide, let’s take a quick look at some of the available fibers and see how they are used to make sails.

Woven Dacron. Made by Dupont, durable Dacron (polyester) is a benchmark fabric that is manufactured in varying weights and can be either “balanced” or “fill orientated.” When the fabric is being manufactured you have yarns running in two directions: along the fabric (warp) and across the fabric (fill.) If you are planning on using the Dacron in a low-aspect sail - for example a sail that has a long foot length relative to the luff - then you probably want a balanced Dacron. In low-aspect sails the loads are not concentrated along a certain area of the sail; rather, they bend into the body of the sail and are distributed more evenly throughout the entire sail. On the other hand, if you are weaving the Dacron to be used in a high-aspect sail, like a blade jib or a mainsail with a very short foot length, then you want the strength of the fabric to be across the panel. This way, once the sail is made you have a concentration of stronger fibers where they are needed - up the leech where the highest loads are. To make a “balanced” Dacron you use fibers of similar strength running in both directions. The fill-orientated fabric will the have larger (read stronger) yarns running across the fabric and lighter yarns running the length of the cloth.

Laminated polyester. Instead of weaving the polyester fibers, they are instead laid in a scrim and laminated to a Mylar substrate. This accomplishes a number of objectives. One of the biggest problems with a woven fabric is that as part of the weaving process the yarns have to go over and under each other. This is called crimp, and once a load comes on the sail the crimp starts to straighten out, the fabric stretches, and stretchy fabric distorts sail shape. Fabric makers attempted to limit this problem by running woven cloth through a bath of resin to impregnate the yarns and stabilize the fabric to prevent crimp. However, over time the resin breaks down, the sail takes on a nice soft feel, and the shape distorts. By using a scrim, the yarns are actually laid into the fabric, pre-tensioned in some cases so that there is no crimp. The scrim is then bonded to Mylar (or Tedlar) so that it cannot move. The Mylar also provides off-threadline strength. To protect the scrim and Mylar, light taffetas are laminated to each side of the fabric, resulting on a robust, low-stretch material that is very versatile and very efficient. Its only drawback is that the manufacturing process is much more intricate than simply weaving the fibers, and the cost rises accordingly.

Pentex. A half-century after Dacron was introduced, Allied Signal (now called Honeywell) developed Pentex, or PEN as it’s known in the trade. PEN is an acronym for polyethylene napthalate. It is a “super-Dacron” combining all the great qualities of Dacron without the one major drawback - stretch. Pentex was developed for the tire and mechanical rubber markets and has several features that make it well suited for sailcloth applications. Aside from being rugged, it has two and a half times the modulus, or stretch resistance, of regular Dacron. This translates into two and a half times less stretch for voyaging sails of equal weight. The early uses of PEN was in a woven form; however, it is better suited to lamination and can be found on small weekend voyagers as well as globe-trotting megayachts. The Pentex yarns are laid into a scrim and bonded to a substrate just like the polyester voyaging laminates. For a high-performance voyaging fabric, Pentex offers real value.

Spectra, Dyneema, and Certran. All three fibers are close cousins, made by different manufacturers, the most recognizable of which is Spectra, made by Honeywell. They are all polyethylene. Dyneema is made in Holland by the Dutch company DSM, and Certran is made in the U.S. by Hoechst. All three have excellent durability; they don’t mind sunlight, flexing, or chafe; and they have an outstanding resistance to stretch, at least initially. Over time the fibers start to “creep.” In other words, they stretch permanently, and the resulting distortion is bad for sail shape. Add to this the difficulties with laminating because of the fibers’ slippery texture, and the problems that occur because the fibers melt at a relatively low temperature, and you end up with a wonderful thread but less-than-perfect fabric.

Before we discuss Cuben Fiber we can take a look at some of the other fibers that have been tried and used with varying degrees of success. Kevlar is the best high-performance fiber, and it has been used with moderate success, especially on big boats where the loads demand it. Kevlar’s weaknesses are exacerbated by two main ingredients of a summer’s day on the water: sunshine and wind (which causes flogging). To compensate, fabric makers encapsulate the fragile Kevlar yarns with rugged taffetas that protect them from the harmful rays of the sun and dampen the bending moment as the sail flaps in the wind. North Sails has recently introduced its Marathon Series, which is essentially the same construction done on a 3DL mold. Ellen MacArthur had these sails on Kingfisher and used them with obvious success. Team Adventure has their Solent made from this construction, and, aside from absorbing water when the Cuben Fiber does not, it appears to be holding up just fine.

Vectran is another interesting fiber. This fine filament was created for the defense industry. The U.S. Navy was looking for a fiber that could be used to tow listening devices behind submarines. The listening device was paid out behind the sub to an exact distance. The noise of the sub’s engines was then tuned out so that the device could listen for other noises. The length of the tow had to remain constant, and the fiber had to withstand adverse conditions. Vectran was the result, and it has been used with results similar to Kevlar. The same goes for carbon fiber, which, as strange as it sounds, will one day be used in voyaging sails. The material has unbelievable resistance to stretch; however, because it is brittle and fragile, it does not like to be bent or flogged - hardly a suitable fiber at this point, but innovative thinking will one day allow it to be used with success. Team Adventure’s Cuben Fiber sails incorporate carbon, and after 17,000 miles they show no signs of wear and degradation.

So what is Cuben Fiber and why might it become a desirable fabric for voyagers? Like most new ideas it will probably take some time before it is accepted as mainstream. When we developed the sails for Team Adventure, a main requirement was light sails that did not stretch and had enough durability to circumnavigate the world without stopping. The benchmark fabric was Spectra. It was rugged and proven, and it offered reasonable shape-holding capability. The problem was that, when we calculated the weight of the mainsail using sufficient Spectra to handle to huge loads of a mega-catamaran, it came to about 1,600 lbs. I have Spectra sails on my open 50, and when you sail alone you become sensitive to minute details. I noticed that even on damp days the weight of the sails increased. Spectra absorbs (and wicks) water, and if you are sailing around the world you can be sure that the sails are going to be wet much of the time.

This led us to Cuben Fiber. The fabric is manufactured in a unique process in which large panels are laid up with up to as many as seven layers of yarns all oriented in certain directions. They are lightly bonded to a Mylar substrate, and then the entire panel is loaded into an autoclave and baked under high heat and pressure until all the layers become one. The newly baked fabric has the feel of heavy plastic with unequalled strength and stretch resistance. We measured it against normal fabrics like Kevlar, Spectra, and PBO (a high-cost, low-stretch, short-life racing fabric) and nothing came close. I attached a strip of Cuben fiber to the antenna of my car and drove around for a month and then retested it - there was no change in its qualities. Most important of all the fabric did not absorb water, and the finished mainsail weighed in at just more than 800 lbs.

Testing proves positive

The testing and retesting provided results that looked too good to be true, but our sail inventory was the only edge we would have on our competition, so it was a choice worth seriously considering. Small amounts of Cuben Fiber had been used in the last Whitbread race, and while we were convinced that it was the way to go for The Race, there was some uneasiness about using a relatively untested fabric. To compensate, we carefully calculated the engineering loads and then added a healthy margin for safety. The corner reinforcement patch was oversized, as were the reef and luff hardware patches. All told it was a reasonable gamble for what we considered would be a solid edge on our competition.

A defining moment came right after the start when Team Adventure sped away from the rest of the fleet. Skip Novak, co-skipper on Innovation Explorer, said it best in a piece for Outside Online. “The raw speed Team Adventure showed off the line was incredible, and we must assume all other things being equal that her sail wardrobe of Cuben Fiber fabric was worth the extra couple of hundred thousand dollars! She literally marched away from the fleet, pointing higher and going faster, as they say.” Skip exaggerated the cost of the sails, not the speed. Our estimate showed an 8% increase over Spectra.

Loads in the leech

Once a fabric has proven itself on a long offshore voyage, it then stands a chance of becoming mainstream, but the question still remains: why do we need these high-tech fabrics when many circumnavigations have been done with Dacron? Before answering that question let’s first take a look at how different fabrics are used within a sail. A woven fabric generally has the strength running across the panel; therefore, it is used to build crosscut sails. This is very inefficient as you end up with the same weight fabric at leech as you do at the luff, yet the loads at the luff are often half that of loads running up the leech, especially when sailing on the wind. If you try to use two fabrics of different weight in the same panel, you end up with a crease running the length of the sail and severe shape distortion over time.

Laminated fabrics have their strength running along the panel, and therefore they can be used in a radial panel layout. This is much more efficient because you can have heavier (read stronger) fabric up the leech and along the foot, lighter fabric through the body of the sail, and really light fabric at the luff where the loads are less significant. This step-down process is an efficient use of fabric and has one tangible advantage - the sails are lighter for the same strength and stretch resistance, and lighter sails are easier to handle and take up less space on board. Consider a couple trying to reef a mainsail in a blow or change headsails. Light sails that are easy to handle and manage go a long way toward prudent seamanship.

Also, in-boom furling systems are becoming increasingly popular, and one main objective of sailmakers is to create sails that roll up tight and have less bulky reinforcement patches. Cuben Fiber, or other similar high-tech laminated fabrics, has a distinct advantage over Dacron. The same applies to weight and windage aloft. A lighter sail that rolls up tighter on the headstay is more desirable than a heavy one that adds to the pitching moment and adds windage where you really do not need it.

So why not just choose a radial sail every time? Another good question with the same answer: you can, but remember that there are two major factors that go into the cost of a sail, the fabric and the labor required to build the sail. In both cases a radial sail is more expensive. The laminated fabric is more expensive to produce, and radial sails require more work to manufacture. Before you decide on one or the other means of construction, give careful consideration to the kind of sailing you will be doing. Think of your budget and your experience level. If you take each criterion and ponder it carefully, it will soon become obvious what makes the most sense for you and your boat. Will it be durable Dacron, pricey polyester, or cutting-edge Cuben?

By Ocean Navigator