Be­yond the Weave

Cruising World - - Contents - By Tim Mur­phy

North Sails’ new 3Di Nor­dac sails bring mod­ern tech­nol­ogy to tra­di­tional cloth.

3DI NOR­DAC sails, from North Sails Group, are not cre­ated from wo­ven cloth or lam­i­nated strings on film; rather, they are laid up in a seam­less three-di­men­sional com­pos­ite struc­ture — very much like your boat’s hull and deck.

“There is noth­ing new un­der the sun.”

That idea, from Ec­cle­si­astes, was new just over 2,400 years ago. Wo­ven cloth was new about 25,000 years ago. Polyester was in­vented in 1941, and since around 1950, wo­ven polyester cross-cut sails have been the reign­ing tech­nol­ogy on cruis­ing sail­boats around the world. (Rac­ing sail­boats are a dif­fer­ent story.)

3Di Nor­dac tech­nol­ogy, in­tro­duced this sum­mer by North Sails and cre­ated for cruis­ing sailors who truly want to sail, is some­thing new un­der the sun.

The Trou­ble with Weav­ing

“The big dif­fer­ence be­tween a good cruis­ing main and a bad cruis­ing main,” says North Sails CEO Dan Neri, “is the twist pro­file, where the top of the sail is the most open place on the sail. Then it’s pro­gres­sively less open when you go down.”

On a nor­mal Dacron sail, where you don’t have any con­trol of the stretch, the mid­dle of the leech be­comes the most open when it’s time to twist the sail, he says. “That pulls the top of the leech in, which gives a deeper head and open mid­dle. And that makes the boat heel more.”

The ques­tion for sailors and sail­mak­ers, then, is: How do you cre­ate a sail that holds that de­sir­able shape over time — a shape that de­liv­ers the most for­ward-driv­ing lift with the least speed-killing drag?

The his­tory of sail-mak­ing is marked by in­no­va­tions in both fiber and cloth. The year 1851 was a wa­ter­shed year. That’s when the schooner Amer­ica trounced 15 Bri­tish con­tenders for the Hun­dred Guinea Cup, later called the Amer­ica’s Cup. While all the Brits were fly­ing sails made from flax (linen), Amer­ica demon­strated some­thing new: cot­ton (can­vas) sails. Re­tain­ing a flat­ter shape, the sails con­trib­uted to less heel­ing mo­ment, a drier fore­deck and — most no­tably for an is­land em­pire held to­gether by its sail-pow­ered Royal Navy — a point­ing an­gle that was 6 de­grees closer to the wind than that of the near­est com­peti­tor.

It was an­other transat­lantic com­pe­ti­tion, some 90 years later, that pro­duced the next ma­jor in­no­va­tion in sail­mak­ing. This was the quest to com­mer­cial­ize or­ganic chem­istry. The re­sult was the Bri­tish dis­cov­ery of poly­eth­yl­ene tereph­tha­late (PET) — bet­ter known as polyester. In 1946, Dupont pur­chased the patent and called it Dacron.

Since about 1950, cross-cut polyester sails have been the reign­ing tech­nol­ogy on cruis­ing sail­boats. Through­out this pe­riod, the sail­maker’s goal has been to con­trol stretch. Newer fibers such as car­bon, aramid, Spec­tra or Vec­tran stretch less but bring other down­sides, in­clud­ing cost.

In two-di­men­sional cloth, warp yarn runs length­wise and fill yarns run the width. In a fill-ori­ented cloth, the warp yarns bend, or “crimp,” un­der and over the fill yarns; such cloth stretches less in the width di­men­sion. “Bias” is the di­ag­o­nal be­tween warp and fill. The most typ­i­cal cruis­ing sails are cross-cut sails, made from pan­els of fill-ori­ented polyester cloth. Be­cause they stretch least in the width di­men­sion, the pan­els are aligned per­pen­dic­u­lar to the leech, where the pri­mary loads oc­cur. The trou­ble is, not all of the loads are in that direction, so the sails even­tu­ally stretch into rounder, deeper shapes.

Be­gin­ning in the 1970s, sail­mak­ers found a way to avoid some of the prob­lems in­her­ent in all wo­ven cloth — par­tic­u­larly stretch in the bias direction. They lam­i­nated yarns on a layer of My­lar film (an­other form of polyester). But with rare ex­cep­tions, the down­sides of dura­bil­ity, longevity and cost made lam­i­nated sails, or

“string sails,” more pop­u­lar for rac­ing sailors than for cruis­ers. Lam­i­na­tion, many found, was too of­ten at­tended by its evil twin: de­lam­i­na­tion.

From fiber to cloth, we move from one di­men­sion to two. But sails are three-di­men­sional air­foils. To cre­ate that third di­men­sion of draft, sail­mak­ers cut curved edges into the flat pan­els of cloth in a tech­nique called “broad­seam­ing.” The place­ment of the draft is a fun­da­men­tal dif­fer­ence be­tween good sails and poor sails.

When a for­merly good sail stretches out, its draft slouches aft.

3Di Nor­dac Sails

North’s 3Di sails were new about 10 years ago and born of yet an­other transat­lantic com­pe­ti­tion. Nei­ther a weave nor a lam­i­nate, 3Di is a com­pos­ite of flat tapes of fiber lay­ered in a ma­trix of ther­moset resin, much like your boat’s hull. While wo­ven cloth or lam­i­nated string sails are “load-path” struc­tures in which vir­tu­ous prop­er­ties align more with some yarns than in other di­rec­tions, 3Di is dif­fer­ent. It’s a quasi-iso­tropic ma­te­rial — “iso­tropic” mean­ing that it ex­hibits its prop­er­ties of strength and stretch-re­sis­tance in ev­ery direction.

Dur­ing the 1992 Amer­ica’s Cup event, Bill Koch’s Amer­ica syn­di­cate in­tro­duced a ma­te­rial sub­se­quently called Cuben Fiber. Round yarns, or tows, of fiber (Dyneema, car­bon, aramid) are spread out into a flat tape of side-by-side fil­a­ments. At the time, Cuben Fiber was used in lam­i­nated sails. Then, in 2001, Swiss sail­maker Gérard Gau­tier imag­ined such flat tapes put to a dif­fer­ent use — one that would get rid of the film in the lam­i­nate. In Gau­tier’s ver­sion, the tapes were im­preg­nated with a ther­moset resin that, once cat­alyzed, would hold its shape de­spite heat­ing or cool­ing. The Alinghi syn­di­cate tried Gau­tier’s tech­nol­ogy in the run-up to its suc­cess­ful Amer­ica’s Cup de­fense in 2007.

Be­fore long, North Sails did what Dupont did with polyester: It bought the patent. But the patent was only for the process, which Gau­tier ac­com­plished in two di­men­sions be­fore ap­ply­ing the tra­di­tional broad­seam­ing tech­nique to join the pan­els in a con­cave shape. North Sails’ en­gi­neers adapted Gau­tier’s idea to their own pre­vi­ous in­no­va­tions in sail­mak­ing di­rectly on a 3D mold. The re­sult was to elim­i­nate seams al­to­gether.

Since 2011, North’s 3Di sails — built with such fibers as car­bon or aramid — have been the state of the art for Volvo Ocean Race com­peti­tors and other grand-prix race boats. Speak­ing to dura­bil­ity, Volvo boats pre­vi­ously car­ried 28 sails per cir­cum­nav­i­ga­tion, in­clud­ing three main­sails, says Neri. Us­ing 3Di sails, they can do it with 11 sails and just one main. When Thomas Coville set the solo roundthe-world record at 49 days in 2016, he left the dock with 3Di sails that al­ready had 50,000 miles on them. That’s two full cir­cum­nav­i­ga­tions.

What’s new un­der the sun this sum­mer is the com­bi­na­tion of 3Di tech­nol­ogy with tried-and-true polyester for cruis­ing sailors. With this cloth, sail re­pairs can be done on the dock, us­ing ad­he­sive. There are also no seams, or the stress ris­ers they cause.

Like all new things, we may still have more to learn about how Dacron be­haves in the 3Di en­vi­ron­ment. But it cer­tainly looks promis­ing for cruis­ing sailors who truly love to sail. Tim Mur­phy is a Cruis­ing World ed­i­tor-at-large and a long­time Boat of the Year judge.

Twist pro­file: The leech of a well-built sail opens pro­gres­sively to­ward the top.

3Di sails start not as round yarns but as flat tapes of fiber im­preg­nated with polyester resin. The tapes are then laid out on a three-di­men­sional mold that ap­prox­i­mates the shape of the fin­ished sail, omit­ting the broad­seam­ing tech­nique.

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