Pushing the envelope - in our direction

Kevlar, an aramid manufactured by DuPont, was the first light-weight, low-stretch fibre used in marine applications, and it offered smaller diameter ropes and lighter-weight sailcloth.

However, this weight saving came with decreased durability. Kevlar's major drawback is that when flexed repeatedly, the fibres break and it is also poor at resisting UV degradation. So Kevlar running rigging has only been used where either cost or durability is not the primary goal and in sailcloth it tended to be used for racing sails where longevity was not an expectation.

However, a lot of development has taken place since then and as Ian Brown of the Quantum Sail Design Group points out, ordinary cruising sailors will eventually benefit from the experience gained in high tech racing. He says: “Five years ago most cruising sailors wouldn’t have considered having laminate sails incorporating carbon fibre or aramids, but they are lighter and there is strength where it’s needed.”

Less heel
He adds that cruising sailors don’t always think in terms of having a performance sail, but lighter sails mean that the boat doesn’t pitch or heel as much and baggy sails will also induce excess heel which can be quite intimidating for either inexperienced sailors or those with family aboard.

However, Mr Brown thinks its worth noting that the higher price attached to a high tech sail buys shape retention, which manifests in performance, but not necessarily durability. Although 10 years ago laminates tended to be much more fragile, Mr Brown says that delamination isn’t something seen much now though they can crack and split.

Laminates tend to break down for three reasons, he explains. “Firstly, as the sail flutters and flogs, the film work hardens, gets brittle and cracks. Secondly, the fibres themselves get weakened by continual flexing and thirdly, the sails get weakened through exposure to UV and the elements."

He adds, “With woven polyester (Dacron), you can see that it has worn and gone baggy, but with laminates you can’t always tell how much they are fatigued – and when they fail, they tend to fail catastrophically.” Which can itself be unnerving.

North Sails has a range of sails from panelled laminates for more relaxed cruising followed by a wide span of 3DL products “the lower end of which are suitable for the local club racers as they aren’t prohibitively priced”, says Jeremy Smart. These have simpler yarn layouts and lower density fibres.

New structure
However, the latest development from North are the 3Di sails that at the moment are starting to take a large slice at the top end of the market.

North Sails’ new 3Di sail products, says Mr Smart, are based on a different technology, despite using similar materials to the well-known 3DL sails. To make a 3DL sail stiffer along the leech, the designer adds to the yarn denier running from clew to head to take the strain, but the 3Di (while utilising the same carbon or aramid) has a different structure.

The 3Di sails are of a composite construction rather than a laminate - one piece composite structures just like masts or hulls. This creates a sail that's strong and low stretch in multiple directions with less shape distortion and, as a result, improved performance.

Mr Smart explains another important difference is that the 3Di sails have done away with the Mylar film, because as the sail is now a composite structure the film is no longer required to form a skin. The sails are still moulded using North’s patented process, but using pre-impregnated filament-thick tape that's applied across multiple axes before being thermoformed over the 3D mould.

This is in contrast to North’s 3DL carbon or aramid (Kevlar) sails, which gain durability by using yarns that are coated but not saturated with adhesive: the 3DL production leaves the filaments on the inside of the bundle free to move around when the yarn is flexed or folded and avoids most of the problem of the fibre’s inherent brittleness.

Layered approach
However, the 3Di version is saturated with resin, which means the various layers of the sail need different structures: while the outside needs to stand up to abrasion, the interiors require flex and foldability and, of course, the resins have to follow suit as well to be compatible with each other.

So, the 3Di structure mates either carbon and Dyneema, or aramid and Dyneema fibres. 3Di sails are offered in three basic product types, designated 880, 870 and 670.

The 880 sails are 100% carbon and offer the lowest stretch out of the three options – these are for the grand prix inshore race boats like the TP52s. The 870 comprises a combination of carbon and Spectra fibres (manufactured by Allied Signal) for increased longevity whereas the 670, used by many of the Volvo teams, has aramid fibres under the surface layer.

Filtering down
If this all sounds a bit too upmarket, Mr Smart explains that at some point in the near future 3Di technology will be filtering down. He says: “At present a dozen boats on the Solent have them. In two or three year’s time, I see virtually all those racing boats that have 3DL moving over to 3Di sails.”

A word of warning with the new technology is inevitable. 3Di sails, for example do not "pant" and headsail leeches stay very close to a constant distance from the spreader ends throughout the wind range. So, these stiffer sails simply pass on breaking strains to anything else in the load path because they do not give when pressure is put on the membrane – and it's been found that new technology sails can indeed break halyards and sheets. In fact early 3Di sails have proven so stiff that the company has turned its efforts toward engineering some give back into them for certain projects.

New life for polyester
However, it’s not all about racing. In 2005 North Cloth embarked on a programme to develop a high-performance, warp-oriented woven polyester sailcloth.

The result is the Radian range, which combines low stretch shape holding with the durability, easy handling and mildew resistance of non-laminated woven polyester.

Mr Smart explains that to get this from humble polyester needed a process developed by North which allowed a really high quality material to be manufactured which maintains the laying of very straight, uncrimped warp yarns while the fill is woven extremely tightly around them.

“It’s much more dense than the stuff that goes into the usual crosscut panelled sails, and this means you can design a load-aligned tri-radial sail that performs better and holds its shape longer. It’s also about 15% cheaper than the bottom end of the laminates. Although it will eventually lose shape and some of its performance, because it's woven it has a long life, often upwards of 10 years,” says Mr Smart.

Meanwhile, Vectran fibre is being incorporated into durable woven sailcloth with interesting results.

Long distance
Matt Atkins of Kemp Sails explains that Hood’s Vektron Sailcloth (Hood Sails are made under licence in the UK by Kemp) and Dimension Polyant’s Hydranet are both superb for long distance cruising and for boats that get a lot of use, for instance chartered yachts or syndicate owned boats.

It’s interesting that Vectran fibre came out around the same time as roller furli g and reefing on cruise boats caught on. As an example, Mr Atkins explains that although sail fabrics can distribute loads in a properly designed and reinforced sail effectively when fully set, if used heavily reefed down, the loads are placed onto the single layer of un-reinforced sailcloth so in this instance, having a superior fabric is often a good way to ensure good longer term sail life and performance.

Spectra fibre also helps solve the problem of durability, being impervious to flex fatigue while at the same time having a modulus four times higher than Kevlar. Although significantly more expensive than polyester it has proven to be very useful for large, laminated cruising sails where durability was the prime consideration.

Hybrid weaves
However, it wasn’t until Vektron and Hydranet came onto the market that such hybrid woven sailcloths came into their  own. Not only did they have low stretch and light weight, Vectran has a much higher heat resistance which allowed it to be interwoven with polyester. This last point was something of a breakthrough because the earlier Spectra fibres would melt at the high temperatures needed to stabilise the polyester construction.

Mr Atkins says that in essence, the mix of fibres gives the sails strength, durability and a much better resistance to stretch - one of the main things that spoils a sail’s performance.

These sails are lighter, stronger, and more durable than their laminated Spectra or woven polyester counterparts. As an example, Endeavour's mainsail, at 5,400sq ft, is currently one of the world's largest. The earlier woven polyester sail weighs 1,640Ibs but its Vektron replacement weighs just 950Ibs.

And having been developed first for high load, lightweight durability, it is now being made in lighter weights. Hood’s 6.0oz and 4.0oz have been used for mains and genoas in single-ply woven constructions for yachts as small as 24ft.

Taffeta backing
However, Mark Woodford of Jeckells adds that these days cruising laminates can also have either a single or double taffeta (polyester) backing, which gives a cloth that has stretch resistance and added tear strength, but one that has the performance of a film on film laminate. This mixes happily with Spectra, Kevlar and carbon as the taffeta gives the fibres good flex and better UV resistance.

“With no delamination to worry about the cruising sailor can easily roll or reef the sail knowing that huge pieces of film are not going to start coming off,” says Mr Woodford. With thread going both through the warp and the fill, the added bonus is a diagonal thread - known as the diagonal axis ribbon - which locks the cloth up. “With improved lamination these cloths are hard to beat,” he says.

Changing ambitions
Sailing patterns are changing and according to Mr Atkins, sailors are pushing the envelope a lot more these days. “You need to bear in mind the fact that as yachts have tended to get bigger, so have many owners’ sailing ambitions.” So sails such as the roller genoas of larger boats are being expected to do more work - and this can take its toll on the sail material.

Mr Atkins has a word of warning for the many owners who aren’t giving enough allowance for the harshness of UV light, especially as boats are often being used even more through what was the off-season.

“We all take precautions against the rising risk of UV-related skin problems," he said. "But then we still often see genoas left rolled up on furlers all through the winter and I commonly see mainsail heads and clews protruding from out of their sail covers. The clew corners take all the load, so this doesn’t seem wise.”

He recommends considering adding a sun sleeve cover over the furled genoa, if it can’t be removed. Or repairing or replacing badly fitting or old damaged sail covers and mainsail packaways. “Essentially this is acting sensibly and protecting your investments,” he adds.