High Tech Sail Cloth

High tech sailcloth... the work in today’s sails is done by fibres. These are space-age fibres, however — not grown on a plant or plucked off some furry animal. These man-made filaments can have names longer than this sentence, but it’s easy to get the point across to a layman — just say, “My sail is made out of the same stuff they use in bullet-proof vests and the Stealth bomber.” Even though these fibres were invented for industrial applications — not the sailing market — sailcloth companies have been able to get their hands on some really cool stuff!

The following is a description of some of the fibres used today.

Dacron/Pentex: Dacron is DuPont’s polyester fibre. It’s been around for 44 years and is the cheapest of the sailmaking fibres. While it has great durability, it also is quite stretchy. If you give it a heavy coating of resin, it will stretch less, but then durability is hurt. Pentex is a new blend of a polyester fibre called PEN, made by Allied-Signal. It’s like a “super Dacron,” featuring 2.5 times the stretch resistance while retaining Dacron’s durability. This fibre appears to have a bright future, especially in one-design and club-level PHRF racing.

Kevlar and the aramid family: DuPont’s Kevlar fibre has the longest track record of the ultra-low-stretch fibres in sailmaking. Like most of these space-age fibers, there can be various formulations. Sailmakers typically choose from two different Kevlar recipes: K-29 or the even less stretchy K-49, although K-149 has been employed at the America’s Cup level. The durability of Kevlar sails has improved markedly over the years, but this expensive fibre is still “mildly allergic” to sunlight. Other members of the aramid family include Technora, made by Teijin in Japan for use in industrial drive belts, and Twaron, made by Akzo Nobel in Germany. Both feature roughly similar characteristics to Kevlar.

What is D4?

D4 is a custom sail laminate that provides unmatched flexibility in fibre orientation. Accurate yarn placement and superior lamination ensures better shape retention and improved longevity.

A wide range of fibre and skin components means D4 is the perfect choice for the Grand Prix racer, club racer or discerning cruising sailor.

The D4 Advantage

Curved yarns accurately follow the load paths in the sail.

The yarns in a D4 sail are laid in curves. This results in a sail that is much smoother when set, holds it’s shape better and lasts longer than a conventional panel sail. 

Accurate fibre distribution

Every square of a D4 sail is custom designed to handle not only the principle loads under normal sailing conditions, but those that are generated when a sail is reefed. The yarn map of the D4 mainsail shows the primary yarn array plus a series of load bearing yarns that radiate from the new clew and tack corners when the sail is reefed. This ensures there is no distortion to the sail when reefed, or worse, the breakdown of the laminate that might occur in a conventional panel sail.

Reefing headsails

Headsails can also incorporate reefs. Unlike conventional triradial sails where the yarns radiate from the three corners, D4 headsails can incorporate reefing corners within the laminate. This means that a sail can be reefed in a similar way to a mainsail without the risk of distortion to the sail that would occur if an attempt was made to incorporate a reef in a traditional triradial sail.

Roller furling sails.

D4 mainsails for furling booms incorporate a series of yarns to support reefing loads in the same way as standard D4 mainsails. Conventional sails can’t incorporate large reefing patches as the uneven thickness on the leech inhibits the smooth furling of the sail. The D4 method allows a series of reefing positions to be incorporated within the laminate without creating this problem. Roller furling headsails can also be custom designed in a similar way, with yarns laid to compensate for the loads generated when the sail is furled.

Stronger bond than conventional fabrics or other methods

The thermoplastic resin used in the D4 laminate has stronger bond characteristic than that used in the production of standard sail laminates. Also, as the sections are laminated in a flat form before shaping, there is no practical limit to the external pressure used during the bonding process. This is essential to ensure that delamination will not occur during the use of the sail. It also means the sail can be made considerably lighter than other sails, as less adhesive is required to form the lamination.

Fibre choice

D4 sails are not just for the grand prix sailor. Product development is continuing to ensure the perfect sail is available for the racing or cruising enthusiast. New fibres and custom sail technology will ensure that D4 offers the ultimate in performance, durability and value. Fibres such as High modulus Twaron, Kevlar 49, PBO and Carbon offer the ultimate in stretch resistance for the Grand prix racer while Pentex provides lower stretch than conventional polyester and is an ideal fibre for club racers and cruising applications. 

Farr 40 OD mainsail using HMT & PBO fibres & UV films 

Ultimate durability

Ultimate durability Laminates can include an external polyester taffeta (light weight woven material) that offers the ultimate in durability , improving the flex properties of the laminate and protecting the fibres and films from abrasion and damaging UV rays. These sails can incorporate either single sided or double sided taffetas.

D4 taffeta mainsail, film headsail

Greater sail life with UV protection

The life of most fibres used in sailmaking is greatly reduced due to the harmful effect of light, particularly ultra - violet or UV rays. A number of tests have been run comparing laminates using standard PET films with D4 laminate samples using both clear UV absorbing films and dark grey dyed films with UV absorbers. HMT Twaron samples using standard PET films showed A significant loss of strength after 40 days exposure (37% loss) compared to clear UV samples which showed a decrease in strength of only 13.9% over 40 days of exposure. Interestingly while the grey films showed similar results to the clear UV films, the clear UV films actually showed better results.

Large cruising yacht sails

For larger cruising yachts, Vectran fibre offers incredible stretch resistance with a modulus similar to Kevlar 29 but with much better flex properties. A laminate using light weight taffetas and UV absorbing films ensures protection of the fibres from damaging UV rays and general abrasion. Vectran is the ideal choice for high performance cruising yachts.

The process

Stress maps are produced to analyse the magnitude and direction of the loads within the sail and the effect of these loads on the flying shape (versus mould shape) of the sail. From this analysis the final mould shape can be produced together with the fiber count throughout the sail, and the yarn arrays required to produce the ideal sail structure. The production process begins with large flat sections of polyester films coated with a U.V. resistant resin. The number of sections is limited to that required to accurately create the 3 - dimensional shape. For example a 5 batten mainsail will typically have 6 sections. A computer controlled machine then lays the fibres in accurate curved arrays according to the custom design. When this process is complete, an additional light weight scrim is introduced, together with the top film.

The lamination is then formed using extreme pressure and controlled heat to bond the films and fibers. After curing the sections are placed on a large x-y plotter where the panel edge shaping including luff leech and foot curves are drawn .

The sections are then bonded together to form the complete membrane.

CARBON FIBRE BRINGS EXTRA BENEFITS TO THE D4 SYSTEM

THE D4 sailmaking system, created and developed by Doyle Fraser Sailmakers in Somersby, NSW, has made it a major player on the world sail-making scene, with the innovative product being distributed by more than 40 lofts throughout the world.

D4 sails are created using a range of modern synthetic materials. Over recent years, a family of fibres known as the aramids, the best known of these being Kevlar, has become the predominant fibre in the racing sector of the sailcloth industry.

Now there is a new material in the D4 range. Carbon fibre, in a family of its own, has emerged as the newest and hottest fibre in the industry.

Carbon fibre is a high modulus (stretch resistant) synthetic fibre made from an acrylic containing carbon, hydrogen and nitrogen atoms, which is heated in three successive stages to eliminate all but the carbon atoms. It is naturally black in colour and is essentially unaffected by UV exposure.

Carbon fibre sails were seen for the first time during America's Cup racing in the late 1990s. The carbon fibre laminates provided exceptional low stretch for their weight. However the expensive first prototypes only lasted around 75 tacks, as they were very susceptible to flexing damage.

Doyle Fraser has been quietly working on the integration of carbon fibres into D4 sails for offshore and inshore racing yachts for some time.

"We conducted tests with carbon fibre over 18 months, initially in anticipation of the easing of rules on carbon sails," said sail designer Brad Stephens.

"Over this period we have had a number of test sails in use, which we have been monitoring regularly. After continually testing a range of carbon fibres and developing methods to control the application of the fibres in the D4 process, we now find that we can work with higher-modulus carbon with outstanding results."

Bob Fraser says: "There have been a number of areas in the D4 process that have presented challenges in handling carbon fibre.

"In theory, carbon had potential as a significant fibre in sailmaking for two reasons. Firstly, most carbon fibre material has a modulus (stretch resistance) that is significantly higher than the aramids being used. Secondly, unlike aramids, carbon is virtually impervious to breakdown from ultra violet light.

"The down side of carbon was going to lie in the difficulties of handling the fibre during the manufacturing process and its earlier poor performance through flex, folding and flogging.

"Having dozens of different carbon fibre raw materials with widely varying performance characteristics, choosing the best carbon is one thing; using it effectively is another. The accurate placement of fibres is as significant as the benefits of the fibre itself.

"With the custom D4 system, the load-bearing fibres are distributed in arrays that accurately support the loads in the sail. The real benefit of high modulus (low stretch) fibres is wasted if the fibres aren't used in this way, as with conventional panel sails."

Flex/fold Tests

Carbon-fibre D4 offered Quest significant weight reduction, better shape holding and greater durability

Earlier testing showed poor results when the trial laminates were subjected to break tests after the samples had been subjected to continual flex and folding.

“Continuous developments using different carbon materials and different manufacturing procedures have resulted in outstanding laminate performance that indicates carbon fibre D4 could well be the most effective material for not only racing sails but for premium cruising sails as well,” says Fraser.

"Clearly the laminate we have developed, combining carbon with aramid material, offers not only a lighter sail with superior shape holding through the use of higher modulus material, but all indications are that much greater durability and longer sail life are achieved," says Fraser.

"In comparing the properties of carbon and aramid fibres, it is worth noting that on a `per weight' basis, the carbon we are using has over two times the stretch resistance of the aramid fibres.

"This is not necessarily the case with styles of carbon in laminates being offered to the general sailmaking industry.

"Our testing has shown the degrading of break strength of conventional laminates using aramid fibres to be in the order of 37% after 40 days of continuous light exposure. By using UV-absorbing films in laminates, we have been able to reduce this to around 15%."

The performance of aramids is known to be poor after flexing. Fraser's tests show aramid laminates losing another 38%-40% of initial strength after being subjected to 400 cycles on its flex tester, where the carbon being deployed with its proprietary methods has lost only 4% of initial strength.

Carbon fibre has only about the same initial break strength on a "per weight" basis as the aramids, so a sail built fully utilising the lower stretch resistance of the carbon for half the fibre weight of the aramid yarn would initially only have half the break strength of the aramid sail.

With this in mind, careful consideration is given to how best use the potential of lighter weight, better shape retention and longevity.

Real-life and laboratory testing allows sail designers to construct a series of curves defining the laminate properties, when new and over time.

The intersection of the curves provides Fraser with critical information when faced with the design issues of stretch, strength, weight and longevity - that is, how best to use the fibre for the particular application when faced with these issues.

Given the obvious benefits of carbon, why all these properties, why aren't they being harnessed by conventional laminate cloth manufacturers?

The D4 development team suggest the considerable advantages of carbon-fibre in sail making systems are best harnessed in custom-laid sail systems where the lightweight, multi-filament carbon fibre material can be delivered precisely by the yarn laying machine.

It says that very fine carbon fibre filaments, (comprising up to 12,000 monofilaments) must be delivered in a dry state, where they are free to slide and bend inside the core of the bundle and have developed a proprietary process to ensure this happens in the D4 system. It claims this ability provides the durability and resistance to crimping damage.

By comparison, many conventional laminates are constructed from pre-made scrims. The "crimp" (bending of fibres as they pass over and under other fibres) will diminish the performance of the fibres as they try to straighten and can have a considerably negative effect on the durability of the fibres.

The real gain from D4 sail laminates using carbon fibre can be seen on the water.

"With these continuing improvements and innovations in fibre selections, our carbon-aramid D4 sails are now being used across the entire spectrum, from racing yachts to mega yachts and cruising yachts," Fraser says.

In the 2002 Sydney-Mooloolaba race, the winner, national IMS champion Quest, and the runner-up, Ragamuffin, both used new carbon-aramid D4 sails. They did so because of the significant weight reduction, better shape holding and greater durability, compared with the conventional aramid headsails formerly used.

Lachlan Murdoch's new Swan 80 Ipixuna has a D4 taffetta/vectran mainsail with lightweight D4 carbon/aramid racing headsails, while the 130ft J Class yacht Velsheda won the Antigua Classic and Antigua Mega Yacht Regatta with D4 carbon/ aramid sails.