NEW GENERATION SAILS
North Sails’ 3Di NORDAC
As with most things in life, choosing new cruising sails involves compromise. You can opt for the longer life and lower cost of woven polyester sails and accept that, within a season, they will begin to stretch. You will lose full control because you can’t flatten the sails – and that means more heeling, more weather helm, more leeway.
There are more expensive sail-cloths that weave in stretch-resistant fibres like Dyneema and Vectran, but the very fact that they are woven means they will still stretch as the fibres straighten under load.
Woven polyester sails are by definition low modulus (resistance to stretch), low tenacity (breaking strength) compared to newer fibres, but remain popular because of their comparatively low cost, high UV resistance and high flex resistance. They can take a lot of punishment.
In the early 1980s, another option became available: the panelled laminate sail, which is lighter aloft, holds its shape very well and will deliver better sail control. But it costs more, is prone to mildew and is more fragile.
Its shape-holding ability is delivered by a ‘scrim’ or mesh of polyester or higher-tech yarns like aramid, Dyneema or carbon fibre, sealed onto a thin film, usually Mylar.
For cruising purposes, this is then covered on both sides with tafetta to protect the film and scrim. The scrim is built with straight fibres so stretch is greatly reduced compared to a woven cloth. But once the Mylar film or the scrim is damaged, the sail loses its strength and sooner or later it will fail in a spectacular and expensive way.
BACKGROUND
Since time immemorial, sails have been made from panels of cloth sewn together. That was still the case in 1955 when Dupont released Dacron, a woven polyester sailcloth that replaced cotton canvas as the cloth of choice.
The cloth is still cut into panels and sewn together in the time-honoured fashion, but compared to cotton, Dacron was stronger, lighter and had better UV resistance.
In 1992 North Sails introduced 3DL sails. The big breakthrough was that the sail was laid up on a mould, built in three dimensions rather than two, so its shape could be controlled perfectly.
Also, it enabled the use of continuous fibres along the load-paths, rather than the discontinuous fibres you get if you stitch panels together. The result was perfect shape, hardly any stretch and light weight. The only drawback was that 3DL was a laminate sail, hence fragile.
The challenge was: could they build a moulded sail without using Mylar film?
The breakthrough came when Swiss engineers working for Alinghi’s 2007 America’s Cup challenge laid out fibres and pre-impregnated them with thermoset resin glue, creating featherweight filament spread tapes of pure fibre.
By building these into sail sections, adding extra layers of tape in high stress areas, then vacuuming these onto the mould and heat-treating to activate the resin glue, a one-piece sail was created that was pure fibre and, crucially, no film.
In the end Alinghi didn’t use the shiny, jet black sails but North Sails understood the potential of the technology (then known as Amalgam), bought it and used it to launch its 3Di range of sails.
If you follow ocean racing, you’ll be familiar with 3Di sails. They’re used by most of the boats in the Vendée Globe, and all of the boats in the Volvo Ocean Race. Reliability is not an issue for 3Di. The technology is well-proven.
A NEW WAY
North Sails’ recent breakthrough is the adaptation of this technology to process polyester fibres. The result is 3Di NORDAC, a sail that’s 100 per cent polyester and has all the durability characteristics of a polyester sail.
It has high UV resistance and high flex resistance, but holds its shape because it’s been built with tapes made from straight fibres, not woven ones. Also because it’s polyester, it’s low-cost.
North Sails says 3Di NORDAC is as big a sail-making revolution as the introduction of Dacron in 1955. I spoke to Bill Fortenberry, North Sails’ cruising market manager, and Sam Richmond, an expert from North Sails UK.
CB Was there a big breakthrough, or was this a logical extension of the 3Di process?
BF Both. 3Di has been evolving for six-to-eight years, but noone was thinking of a polyester product. We want to better serve all the market segments and the cruising market is an opportunity for us. How could we help with better sails and better durability? Then a light bulb went on: could we build a white polyester sail in our 3Di process?
It took 18 months to figure out how to handle polyester fibres, these microthin filaments of polyester, in the 3Di process. Polyester is stretchier, which is a benefit as it makes the sail tough and more forgiving, but when you pull it though a machine to make the filament spread tapes, that needs tension so it wants to recoil when the tension is relaxed. Making the tapes was the hard part. 3Di NORDAC blends modern construction and traditional fibres. Rather than weaving, we’re spreading. Rather than stitching, we’re gluing.
CB How many layers of tape are needed, and how are the layers glued together?
BF There’s a minimum of six up to a maximum of 300 layers, on the clew of a superyacht main, say. You make 3Di NORDAC in the same way you’d build a boat on a male mould, with extra structural strengthening where it’s needed. We use a thermoset two-part polyester resin. The heat lamp gets the resin to flow, the catalyst sets it. It can’t be melted if you heat it.
CB It’s a seamless sail, so what are the lines that look like seams, the square pattern?
BF The top two to three layers of tapes on both sides are external protective tapes, running horizontal and vertical, which provide chafe abrasion and UV durability. The outer tapes overlap slightly and that is creating the square pattern.
CB Are the reefs’ tacks, clews and feet beefed up with patches?
SR Reefs are traditionally added as an afterthought. Here we get to lay it up as we’re building the sail, so there is no extra weight where it doesn’t need to be.
CB Are UV strips, webbing tapes and rings stitched in as usual?
BF Tapes and rings are stitched in. We’re still experimenting with the UV strip. It could be stitched, or painted on. These sails have additional external tapes built in, not stitched. That’s not standard, it’s something we’re looking at.
CB Are there any specific care requirements for 3Di NORDAC?
No, you can wash it like you would any Dacron sail. If you poked a hole through the sail you can patch, glue or stitch it back together. Mildew is less of an issue as there are no voids for water to get into.
CB What are the advantages/disadvantages of 3Di NORDAC over standard Dacron?
I can’t come up with a single disadvantage. You’re paying similar money for a polyester sail to get a one-piece moulded sail, which is more durable and less stretchy than anything before, and it feels way nicer than Dacron in the hand. It’s a better cruising experience and the North Sails customer enjoys sailing. We’re often accused of being too performanceoriented but cruising performance is a thing. It involves moving through the water more effectively and efficiently. That means ease of handling, ease of trim and better shape holding because you want less weather helm, less leeway, less heel. Less stretch means more control. Cruising performance also means durability, and 3Di sails are proven to last.
CB Without seams, will these sails be lighter that similar panel sails?
It should weigh the same as a cross-cut Dacron sail, but with more strength and toughness. It could be lighter for the same strength as a cross-cut sail. The stiffness that comes with 3Di sails makes furling easier, stacking on the boom is a little different at first. The additional strength is built into the structure, with many layers of tape at the corners and reef points. Even the batten pockets are built in. The pockets are closed at the leech, the batten slides in from the luff.
CB Have you had any failures yet and, if so, what was learned?
Yes, we had some luff slides tear out. We’ve made about 50 3Di NORDAC sails and those would have been in the teens. Where slides attach to sails, we use grommets and webbing straps. We learned we needed to build up the fibre mass more than we expected where the slides attach so we built up the structure in that area.
CB For potential customers, how are you backing up your faith in 3Di NORDAC?
All North Sails have a one-year warranty on defects in quality or workmanship, and a year’s free sail care. Depending on use
“You’re paying similar money for a polyester sail to get a one-piece moulded sail.”
CB For potential customers, how are you backing up your faith in 3Di NORDAC?
BF All North Sails have a one-year warranty on defects in quality or workmanship, and a year’s free sail care. Depending on use and care, we guarantee the structure of the sail beyond that. Cruisers expect sails to last six-to-eight years or more and 3Di NORDAC is engineered accordingly.
CB Why are you sending out measurers to everyone who orders a sail? Aren’t those measurements already known?
BF Every 3Di sail is a custom sail. There is a base aerodynamic model but the aspect ratio and size is different so the mould on which the sail is laid up changes for every single sail. No two boats are the same. It’s the same service any race boat would get.
CB It sounds expensive. Will cruising sailors be able to afford them?
BF We’ve never been the least expensive sailmaker but we are pricing 3Di NORDAC within our existing Dacron product family to be affordable on small and mediumsized boats. Customers will be pleased with price and value. The racing guys tend to occupy the moulds in racing season, so you’ll get a better deal if you order outside the first half of the year. B