NORTH 3Di: FREQUENTLY ASKED QUESTIONS
You've got questions? We've got the answers on why North 3Di sails are the most advanced sails on the water.
Thin ply, zero-Mylar construction, spread filaments, thermoset resin. A lot of technology goes into a 3Di sail, and it's exactly what makes 3Di fundamentally different from anything else on the market. Here are the answers to the questions we hear most.
Q: WHAT IS THIN PLY?
A: Most sails are built from woven cloth or laminated film, and both rely on yarns: bundles of fiber. Under load, those bundles straighten and settle before the fiber itself takes the strain, and that's stretch. Thin ply removes it. The same high-performance fibers are spread out into ultra-thin plies of perfectly straight, flat filaments, each finer than a human hair, so they carry load the moment it's applied. Those plies are then laid exactly along the sail's load paths, putting material only where it's needed. The result is less stretch, lower weight and a sail that holds its shape longer. Thin ply is the foundation of North's most advanced sail technology, starting with 3Di.
Q: IN 50 WORDS OR LESS, WHAT ARE THE ADVANTAGES OF A 3Di SAIL?
A: A 3Di sail is built and cured as one piece in its finished three-dimensional shape. With no Mylar film, which behaves differently from the fiber it's bonded to, everything works as one. Less stretch, less weight, strong resistance to UV, chafe and flex, and a shape that lasts.
Q: WHAT MAKES THIN PLY POSSIBLE?
A: Spread filament technology. A filament is fiber in its purest form: a single, continuous strand. Conventional sailcloth bundles thousands of filaments together into yarn. We do the opposite, spreading them flat and side by side into thin ply tapes coated in thermoset resin. Most 3Di tapes blend multiple fibers, and North has a library of over 50 blends, so we can pair the strength of one fiber with the flex resistance of another. That lets us fine-tune the composition within each sail, balancing performance, durability and weight for how it will be sailed. The result is a sail that's exceptionally strong, yet remarkably light.
Q: I'VE HEARD 3Di CALLED HI-RESOLUTION SAILS. WHAT DOES THAT MEAN?
A: Thin ply tapes are robotically placed in precise vectors, meaning each one has an exact length and direction, so material follows the sail's loads exactly. Ply concentration varies continuously across the sail, adding strength where loads are high and saving weight where they're not. String sails take a much cruder approach. Their yarns are laid between layers of film, and the film has to fill the gaps between them, a technology that dates back to the early 1990s. The difference is like a photo from a 90s digital camera next to the image on your phone today. A 3Di sail is the sharp one: 70% fiber, 30% resin and no dead weight.
Q: WHAT IS THE THERMOSET RESIN USED IN 3Di SAILS VS. THE THEMOPLASTIC GLUE USED IN STRING SAILS?
A: 3Di sails are bonded with thermoset resin, a two-part system that cures through an irreversible chemical reaction under heat and vacuum pressure. Once cured, it's locked in for good, unchanged by heat, moisture or UV. Because the filaments are spread flat, the resin coats every one of them along its full length, for maximum bonding area. Film and string sails rely on thermoplastic, or hot-melt, adhesive. Like candle wax, it softens again with heat and breaks down over time under moisture and UV. And because it's bonding round, bundled yarns to film, it only grips the outside of each bundle, so there's far less contact and much weaker adhesion.
Q: WHAT MATERIALS DO YOU USE IN 3Di SAILS?
A: The four core fibers are carbon, aramid, Ultra PE and polyester, and the right mix depends on the boat, how it's sailed and the performance goals. Each starts as bundled yarn, which is reverted back to micron-measured filaments, fully coated in thermoset resin and spread in a single layer to create 200 mm wide tapes. Some fibers are chosen for strength and low stretch, others for their ability to flex and recover. But the raw material is only part of the story. What makes the difference is how North turns those fibers into thin ply and places them in the sail.
A close-up of a thin ply tape: individual filaments spread side by side into an ultra-thin layer.
Q: ISN'T 3Di STILL NEW, UNPROVEN TECHNOLOGY DESIGNED FOR RACERS?
A: 3Di has been commercially available for more than 16 years, and over 53,000 3Di sails have been built. They've been used in everything from round-the-world races to offshore cruising. Because every 3Di sail is engineered tape by tape, the same process can produce sails with very different characteristics. That's what makes three distinct 3Di product lines possible. Each uses its own fiber blends and surface finishes, fine-tuned for weight, durability and longevity in a different type of sailing.
Q: DOES A SAIL NEED TO HAVE CARBON FIBER TO BE CONSIDERED HIGH-PERFORMANCE?
A: Not at all. Some of the highest-performance sails in the world contain no carbon. Today's foiling IMOCAs and 100-foot Ultim trimarans, the most advanced offshore boats on the water, race on 3Di sails built without it. Before 3Di, the accepted formula for performance was simply more carbon. That changed in the 2011–12 Volvo Ocean Race, when six of the seven boats sailed 40,000 nautical miles on aramid and Ultra PE 3Di sails with minimal damage. Carbon is still the right choice where every gram counts, such as in the America's Cup. But thanks to thin ply, choosing a more durable fiber no longer means giving up performance.
Before 3Di, it was widely accepted that the formula for high performance was, simply, more carbon. This long-held belief was disproven during the Volvo Ocean Race 2011-12, when the relatively new 3Di technology was given a heavy remit – to carry six of the seven boats 40,000nm, cross the equator four times, and encounter boat-breaking conditions. With minimal sail damage, aramid-dyneema 3Di sails exceeded the expectations of both the competitors and North Sails. And simultaneously challenged the idea that if you wanted to go faster you’d turn to carbon to build a lighter sail and accept the risk of it breaking when subjected to extraordinary shock loads or flogging. Suddenly, after the race, it was evident that performance no longer came at the expense of reliability.
Q: WHY DOES A 3Di SAIL COST MORE?
A: The cost comes from how it's made. Thin ply tapes are robotically placed along the load paths, and the whole sail is consolidated on a full-size mold in its three-dimensional shape, then cured. That process takes more material engineering and more equipment than cutting and seaming panels. The return is shape retention. A 3Di sail resists the gradual stretch that makes a conventional sail slower over time, so more of its working life is spent close to its designed shape.
