Cruising laminate sails: tips for choosing and buying

Cruising laminate sails: tips for choosing and buying

Ideal weather for a boat trip: almost cloudless sky, fresh breeze of about 6 knots and calm sea. The yacht goes with a slight heel to the sidewind, the crew is sitting relaxed in the cockpit, and the skipper has just risen with a beer, when he suddenly freezes for a second. Immediately after that, he shoves the bottle into the pocket of the winch handle, casts an appraising glance back at the stern, and mutters a little irritatedly: "Get your feet off the shoulder strap and the towel too!"

The team immediately understands what's going on: regatta - a competitor on a similar-sized yacht approaches from behind. He grows quickly, despite the skipper's efforts in pursuit of the gikshkot and sheets. And the climax: he pulls himself up, as if mocking (out of spite), to the leeward side, and soon after that his stern is shown.

And then the skipper remembers again: when at the beginning of the year he took the sails from repair (as usual, it was necessary to hem some lat pockets and repair the worn luff), the sailmaker pointed out tears in the area of the luff of the mainsail, the depth of the profile shifted back. As a result: soon it will be necessary to think about a new sail. These were the only arguments the skipper could not or did not want to accept, as with the exception of a few mildew stains the sail still looked impeccable - and the sailing masters ultimately only want to sell their sails.

Bavaria Vision with triradial-cut cruise laminate sails. Clearly visible: thinner fabric around the luff

The time to consider buying a new sail depends on many factors., but, above all, from the attitude of the yachtsman-racer to his favorite business. If he enjoys a clear trimming sails, that is, to use and squeeze out to the full the potential of seaworthiness in the hull, spars and rigging, he must certainly study the technology for the production of sail fabrics and the creation of sails. And the better he masters this knowledge, the more likely it is that the right decision will be made during the race.

"Classic" sail consists of polyester fabric (dacron), which is woven on modernized shuttleless looms with a roll width of up to 1.39 m using the technology of the method of transverse and longitudinal threads.

A long thread running along it is called a "lobular thread" or "warp", a thread passing under and above it is a "transverse thread" or "weft". The longitudinal threads twine around the transverse threads and create a bond for the fabric. After each passage, the transverse threads are firmly attached to the predecessor, so that a dense fabric with fine holes is obtained. After that, the sail fabric is subjected to other treatments, during which it is heat-treated in huge machines and shrinked, rolled (calendered) with a multi-ton press and, in the end, is sealed (compacted) with resin.

All of these procedures have the ultimate goal of making the woven fabric as stretchable as possible and ensuring perfect flatness. And so that the sailing master can process it without errors, the roll of fabric must lie on the table evenly smooth and without wrinkles, like a sheet of paper.

The problem with this type of sail fabric is that it is woven. Since the longitudinal thread is twisted around the transverse thread in a small arc, it is more stretched than the relatively straight transverse threads. An even greater disadvantage is the inability of the material to withstand diagonal loads effectively enough. Unlike warp and weft, whose stretch can be adjusted using thicker threads, only compression is left for the diagonal, which makes the fabric virtually airtight, as does the resin that holds the threads together.

As long as the sail is new, this method works fine. But over time, or rather, after two, maximum three seasons, the resin becomes brittle and crumbles from loads causing bending, ultraviolet radiation or impacts. The firm connection is weakened and the strength in the diagonal direction is accordingly reduced. Outcome: the profile created by the sailmaker loses its ideal shape. Equally small stretching in each direction is only briefly possible with woven sail fabrics and, therefore, the loss of a productive sail profile is also a matter of time. Since the transverse yarns running almost evenly along the length have minimal stretch, the woven fabrics are sewn parallel to each other, that is, at an angle of 90 degrees to the heavily loaded leech.

Deep diagonal folds extending from the clew corners signal tissue fatigue - despite large reinforcements

This type of cut, the parallel cut, or "crosscut" has a drawback: a sailmaker can only use fabric of one strength. In the sail, the forces arising under the wind pressure are distributed very differently: at the mainsail, these forces act to a maximum extent in the leech area, since the load on the leech and leech is more or less reduced due to their attachment to the mast and the boom. In addition, the leech is additionally heavily loaded from the movement of the sheaves and the boom guy. In order not to make the sail too heavy, all that remains is to reinforce the leech area with overhead sheets of a large area with bows. This also applies to the area of the masthead, tack and clew, as well as around the leech and leech eyelets. All these measures, although they guarantee the durability of the sail fabric and, consequently, the sail itself, do not in any way affect the relatively short service life of the sail profile.

During the past 20 years, however, materials have been developed that have revolutionized the sewing and manufacturing process of sails. These are the so-called high modular aramid fibers (kevlar, twaron, technora), modified polyester (vectran or pentex) or polyethylene (dyneema, spectrum) and carbon... Compared to high quality fibers polyester (dacron, trevira, diolen) they are 20 times less elongated and three times stronger to break. One more innovative solution can be added to all this: mylar film. It consists of the thinnest polyester film, which is not only very strong, but also hardly stretches in the direction of the load. At the same time, the development of gluing techniques is moving forward, so that with the help of all these materials new possibilities have opened up for sailors.

The material determines the cut

The sailcloth could now be made stronger by gluing the mylar film between two layers of polyester canvas (dacron) like a sandwich. Thus, it, in principle, assumed the role of a bonding connection between the canvases as a resin applied to the outer layer, but at the same time led to increased strength and reduced extensibility, primarily in the diagonal direction of the sail sheet.

Therefore laminated sails less susceptible to shocks, smoother to operate and easier to maintain when hand cleaning. Such cruise laminates do not allow you to save weight, but guarantee that the ideal profile shape remains at least twice as long.

Originally invented only for relatively short-term participation in regattas, laminate technology continued to develop: between two mylar films, the Kevlar threads were not tightly located to each other in the longitudinal and transverse directions, and at the same time the warp was strengthened with thicker threads. Thanks to all this, for the first time a minimum elongation was obtained, combined with a correspondingly high strength and ideal profile shape. And from that time on, these canvases began to be used along an unlimited length in the longitudinal direction, so the so-called radial cut appeared.

Cut seams, with their extremely low stretch and strong Kevlar threads, can now flow radially from three sail corners (triradial cut) to the transverse butt seam in the middle and are therefore more efficient in directions of force than parallel cut. In the heavily loaded area of the leech in the radial cut, the fabric panels are also applied vertically in their strong longitudinal direction and are thus positioned more advantageously in the direction of the main load, that is, less diagonally to it.

And in the end, thanks to this  "Patchwork method" it becomes possible to use a lighter fabric for less stressed areas the sail remains effective in light winds, its overall weight is reduced and the steering becomes easier with less effort.

In the meantime, sailors have a huge selection of laminates at their disposal. For example, the largest manufacturer of sailing fabric, a German company Dimension-Polyant, offers over 300 types of products. Thanks to this, the sailing workshop can fulfill the wishes of both the owner of the Optimist and the superyacht. Both especially light sails with a comparatively durable profile for sport sailing are possible, as well as coarse sails made of extra strong fabrics for cruising sailing with external protective materials.

For yachtsmen, the palette of laminate selection can, at first glance, be confusing and incomprehensible to them. In principle, almost all laminates have a similar structure. After all, the goals and quality characteristics that need to be achieved are the same: to produce the most durable and lightweight sails, the profile of which would also retain its shape for a long time, and which would be easy to fly for a small crew.

All these qualities, however, cannot be found in one sail to an equally high degree. For example, a rough-and-tumble laminate sail with an outer layer of taffeta protection for yachts up to 40 feet is unlikely to be lighter than a commensurate woven sail. But the degree of preservation of the profile shape will be many times greater.

On the other hand, woven fabrics are much more durable than laminates - depending of course on how carefully the sail of one kind or another is handled. When choosing fabric for a new sail, compromises must be made as with choosing a new yacht. For those who love sport yachting and find value in good sailing performance, there is only one choice: laminate sails with a long-lasting profile and thus yachting pleasure.

Why does a performance profile have such an impact on yacht performance?

Ideally, the deepest profile is in the toe-third of the sail, while towards the leech it becomes as flat as possible. As a result, the traction components are directed substantially forward, ideally at an angle between 38 and 42 degrees. The boat can go as steeply as possible towards the wind and at the same time develop maximum speed relative to the water. And thanks to the forward thrust, the yacht is balanced with correct heel, rudder pressure and rudder position remain in the green zone.

Good sailing performance ensures not only the most comfortable sailing, but also safety, for example, to catch a dangerous situation in which there is a risk of being nailed to the leeward bank, or to bring the yacht to a port before dark, which is difficult to take a course for.

If the sail fabric loses its tensile strength, the maximum depth of the profile cannot be kept in the place originally assigned to it; it is transferred gradually back over time. Because of this, the direction of the thrust also changes: it becomes more or less directed across the diametral plane. As a result, roll, angle and pressure on the rudder arm increase, while the stroke relative to the water, on the contrary, decreases. Due to the change in profile, the leech area becomes more and more rounded, the air flow changes direction greatly, and at the same time the gap between the staysail and the mainsail becomes narrower.

Heading angle increases the sails have to reef too early. With such sails, the yacht cannot go steeply enough, the skipper must accordingly tilt into the wind. Otherwise the yacht will become too slow, the yacht will deviate too much, and the yacht will bury its bow on the wave.

How does laminate sails achieve superior dimensional stability compared to woven sails?

As we have already mentioned, the action of forces in the laminate fabric is mainly absorbed by the so-called canvas. "Scrim" (non-woven spun sheet of high modular fibers glued to a film). Every year the threads used for the scrim canvas are improving. First of all, aramids under their own names Kevlar, Twaron or Technora have become extremely insensitive to UV and bending loads, and thus more durable, which is also interesting for cruising yachting.

In laminates, among other things, similarly low-elongation and tear-resistant fibers from modified polyester with their own names Vectran and Pentex are used. Even better qualities are fibers or webs made of modified polyethylene under the proper names of dyneema or spectrum. This material is the most resistant to UV and kinking, and is also lighter and does not absorb water. The best characteristics with the highest modulus of elasticity (see "Qualities of materials used in laminates") have carbon filaments.

The disadvantage of a very expensive material: the fibers react too sensitively to lateral uneven loads, for example, when the sail hits the shrouds. This can lead to breakage of the fibers and thus to a loss of the effective profile.

Some examples of how to create cruise laminates with radial cut:

Laminate series Dimension-Polyant "DC" warp-oriented, i.e. longitudinally reinforced canvas "Scrim", covered with mylar film on both sides, which guarantees a strong connection. To protect against rough handling, the outer surface is made of taffeta, which, among other things, is provided with a UV and mildew resistant coating. The tensile strength of this fabric is also improved by the ripstop technology, in which reinforcement threads are crosswise inserted into the fabric structure at 5 mm intervals.

This weaving method is used by default in spinnaker sail fabrics as it prevents further tears in the sail from increasing. In addition, taffeta (thin dacron fabric) protects films and fibers from sharp breaks and is responsible for better softness in the hands and easier sail control.

Special qualities Dimension-Polyant suggests in the model "DYS": The backing of this laminate is composed of a dense Dyneema fabric with specially reinforced fibers towards the backing for a radial cut. The extremely low-stretch and tear-resistant fabric is covered with mylar film on both sides and protected from the outside by ripstop taffeta with reinforced dyneema threads in the direction of the warp. This strong, long-lasting, but very expensive fabric is recommended by the manufacturer especially for cruising sails, which withstand high loads and rough handling for a long time.

British firm Bainbridge, another of the world's leading manufacturers of sailing fabrics, also offers a wide range of specialty cruise laminates that follow a similar principle. The simplest and cheapest laminate "CLP" consists of high-strength polyester canvas "Scrim"glued in mylar, with a taffeta outer surface that protects against ultraviolet radiation. The manufacturer recommends sails made of these fabrics for yachts up to 45 feet, and with a less stretchable pentex sheet for yachts from 60 feet in length.

Best Bainbridge Fabric for radial cut with markings "CLCFG" has a more comprehensive "Scrim": Weft direction is alternated with thin technora and thick carbon yarn, warp of thick carbon yarns and criss-cross on each other in a diagonal direction of dyneima fabrics. The layers are connected to each other using mylar film and protected from the outside with taffeta or dyneema cloth. This very expensive laminate is recommended by the manufacturer for performance cruisers up to 100 feet.

Other major sail makers like North Sails, Elvstrom Sails, Doyle or UK for their needs they produce their own fabrics, which, however, are assembled according to a similar principle.

Modern level of development of membrane technology

As already mentioned, in radial cuts, they try to expand the laminate strips so that they largely pass in the direction of the main load lines. The better this is done, the easier the fabric can be selected. But even with the most complex and expensive cuts, this can only be achieved relatively, since the main forces largely pass from corner to corner along very differently curved curves. In addition, the required transverse butt welds cause discontinuities in the load distribution, thereby creating stress zones and greatly reducing the durability of the profile.

This is especially true for reefbers, whose grommets in the area of the leech and leech, as well as in the tack and clew corners, must be reinforced, because the same forces act on the reefed sails. After all, if a yacht, after reefing, gets into the same conditions as before reefing, the reefed sail is loaded in the same way, or even more.

If the high modulus fibers can be laid out exactly in the direction of the load distribution, that is, where they are needed, the sails can be constructed much more easily with adequate profile durability compared to the complex patchwork method of creating radial sails. Films contribute only slightly to tissue stability. Their main function is to sandwich the fibers, that is, to glue to each other, while the woven taffeta makes the sail fabric convenient for hand cleaning and protects this bond from UV radiation and harsh handling.

This so-called "Membrane technology" was developed back in the mid-80s by an American yachtsman, a participant in the America's Cup, Peter Konrad... He first came up with the idea of sticking fibers in the direction of computer-calculated load lines on the film for a particular sail. This is how the first hand-crafted and very short-lived test sails were created, which, however, met and even exceeded the set expectations.

After that, Konrad developed in his company Sobstad the equipment necessary for sewing the sails and patented the process as "Sobstad-Airframe"... When his companion Tom Widden, tactician at Dennis Conner, moved to North sails, he developed the 3DL method there, in which he laid out the fabrics of the sail fabric in a shape that matched the profile of the sail, and glued them. But, despite this, by a court decision North sails had to pay for Konrad's patent. Later Elvstrоm Sails also bought a more advanced method "Genesis" and until 2007 produced the so-called membrane sails "Genesis"until they were replaced by their own development under the signature Elvstrom Membrane Technik, EMT.

Membrane sails "3DL"Used initially only for America's Cup and pure racing yachts, North Sails has optimized for cruising yachts over the years, making sails more durable and easier to set up - and above all, generally available. In the meantime, other sailing masters and sail fabric manufacturers joined them with their developments for the production of membrane sails, such as Dimension-Polyant with the D4 series and the already mentioned company Elvstrom Sails with EMT, to name only the market leaders.

Fingulf 36 with sail from NorLam, an easy-to-handle cruise laminate reinforced for radial cut towards the warp

PET Polyester (proper names: dacron, terylene, trevira): A very tear-resistant and low-stretch material, which is especially suitable for sailing fabrics. It has high UV resistance, excellent fracture resistance and is relatively inexpensive.

Pentex: It is a modified polyester with 30% less stretch than polyester with the same tensile strength. Fibers can be woven and are often used in a nonwoven spun sheet of strands. Pentex is the cheapest alternative to other high modular fibers, but much less productive.

Vectran: The light brown material is also a modified polyester with a high modulus of elasticity, almost zero permanent elongation, fracture resistance, tear strength and abrasion resistance. Compared to polyester, Vectran is less resistant to kinks and UV light. However, it is more tear-resistant, more fracture-resistant and more expensive than aramid.

Aramid (proper names: kevlar, technora): Kevral was invented by Dupont in 1965 for the manufacture of sails and has been continuously improved since then, mainly in terms of kink and UV resistance. Golden yellow Kevlar is stronger than steel in specific characteristics, and therefore five times stronger than polyethylene and twice as strong as pentex, but more sensitive to fractures and abrasion than polyester. Aramid fibers, moreover, are less resistant to UV light and therefore, like Vectran, must be protected with UV filters that contain taffeta and resin. Kevlar is used to make tight, narrow woven fabrics that can be adhered to mylar films.

Twaron: It is an aramid with modulus of elasticity similar to Kevlar, but more tear-resistant and UV-resistant. The threads are also yellow. About 20 % more expensive than Kevlar.

Technora: This aramid is slightly less tear-resistant than Kevlar, but more fracture-resistant. The filaments are dyed black and thus obtain a high level of UV resistance. Black Technora is often used in laminates to reinforce in a diagonal direction in front of a layer of longitudinal and transverse threads. A little more expensive than twaron.

Modified polyethylene (proper names: dainima, spectrum): Fibers from this material have the highest tensile strength and modulus of elasticity compared to all previously mentioned fibers. They have the highest UV resistance after carbon, very resistant to abrasion, lightweight (buoyant), as well as not susceptible to kinks.

The disadvantages of these very expensive fibers: if they are evenly overloaded over a long period of time, a so-called "crip" is formed - the fibers do not withstand the load, lengthen and eventually break. This disadvantage only becomes apparent when a very light sail fabric is selected. Dyneema / Spectra yarns, like Kevlar, can be processed into extremely tear-resistant and low-stretch woven fabrics ("Hydra Net" from Dimension-Polyant), but are the most expensive after carbon.

Carbon: Multifilament yarns made from carbon fiber have an even lower tensile index than dyneema / spectra fibers, but with slightly less tear resistance. They are almost insensitive to ultraviolet light and some modifications of these fibers achieve high resistance to breakage. Lack of carbon fiber: Strong lateral impacts on the yarn, such as when the sail hits the shrouds, can break. Due to the high demand all over the world, carbon is at least a third more expensive than dyneema.

Fiberglass: Like carbon fibers, fiberglass fibers are composed of many thousands of filaments, which, even after being processed into a laminate, remain loosely connected to each other. This makes them flexible enough to withstand bending stresses. Fiberglass, like carbon, is almost insensitive to ultraviolet light, extremely low-stretch, tear-resistant and 20 percent cheaper. However, the tensile index is 4 times that of carbon fiber, and fiberglass is significantly heavier. Therefore, many sailmakers advise using lighter carbon for yachts from 45 feet in length.

Text: Michael Bohmann

05.04.2012