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North Sails is the only sailmaker in the world to build sails on three dimensional molds. The first version of this pioneering technology, known as 3DL, was introduced in 1992. 3DL sails revolutionized the sailmaking industry and dominated the racing market for over 20 years because they were lighter, stronger, smoother and lower stretch than any sails previously produced.
Today, most sailors have heard of 3D molded sails, but why are they so much better than traditional 2D sails? Without getting too technical, let’s look at the details to explain the difference.
3D sails are created on full scale, shapeable male molds. This means the structural materials and the shape of the sail are set into the finished membrane together – at the same time – in 3D space. 2D sails are constructed by piecing together flat panels; the desired shape is built in by curving the edges of each panel before joining them together.
Panel sails and 2D membrane sails are identical from a design and shaping standpoint; sail shape is created through luff curve and broad seaming. As a result, each primary structural yarn is interrupted at each joint or seam. Each joint becomes a stress riser, a concentration of load that engineers typically try to avoid. With panels and fibers bent at each joint, not all of the filaments within that yarn are working together. It doesn’t matter whether a sail is crosscut or tri-radial in construction; the load cannot be uniformly absorbed by an interrupted series of yarn sections, because the more highly loaded section of yarn at each of those bends stretches more. Stretch caused by the uneven loading of primary yarns is the inherent disadvantage of 2D panel sails.
With 3D sailmaking, each yarn (3DL) or filament (3Di) is laid in the same glass-smooth arc that it will assume when in use. There are no stress risers. The result is even loading across the sail and less stretch for a given yarn density, weight, and strength.
Another advantage of 3D is that overall stretch resistance (shape holding) is largely dependent on the amount of yarn/filament used. It’s easy to make a sail lighter by reducing the yarn content, but it is the ratio – weight to shape holding ability – that is the key attribute. 3D sailmaking allows fibers or filaments to be laid in the optimum place and orientation for shape holding.
The secret of 3D sailmaking is forming a one piece sail from fibers and adhesives, as opposed to constructing a sail in pieces from rolls of sailcloth. 3D shaping is the primary factor that explains the success of 3DL and the fundamental difference of 3D sailmaking. It’s also one of the key reasons that 3Di became the next logical step and a natural evolution of the concept.
The Evolution from 3DL to 3Di
3Di evolved out of 3DL, North’s ground-breaking technology of building sails on full-scale, three dimensional molds. From a technical standpoint, the biggest difference between 3Di and 3DL is that 3Di removes the mylar film and its “parasitic weight.” That parasitic weight can then be replaced with fibers—more carbon, more spectra, more aramid—that further improve shape holding and longevity.
3Di also uses separate filaments, rather than yarns, which absorb load more efficiently because they are straighter. By combining straight fibers (carbon with flex-resistant spectra, for example), the two reinforce each other, even though they are not twisted together into one yarn.
Another key 3Di enhancement is the drastically expanded ways in how the filaments can be deployed. The enemy of shape holding and longevity is changing and uneven loads, caused by variables like wind strength and sheet tension. By situating the right material in the right place, designers can increase a sail’s life expectancy.
3DL (with yarns laid in various arrays) allows far more flexibility in material location than a panel or 2D sail. And nothing in sailmaking compares to the possibilities of 3Di, where the filaments are laid down with a gantry in any length at any angle. 3Di structure is a radical departure from 3DL because designers can put the best material where it is most needed. And since 3Di can be designed to account for compression as well as strain, no other sail today can provide as much shape-holding duration and overall longevity.
3Di leaves North designers with the very pleasant choice of designing a sail that’s either lighter than 3DL with the same stretch resistance, the same weight as 3DL with increased longevity—or even somewhere in between. Ounce for ounce, 3Di sails have significantly more resistance to stretch than any other sail made in the world today.
Finding the 3Di Sweet Spot
All sails, whether paneled or molded, have a sweet spot: a wind range where they perform at their best. Because 3Di sails are thermo-molded in their designed flying shape, they pressurize—assume their optimum shape—earlier in the wind spectrum. This helps the boat to accelerate faster out of tacks or other down-speed maneuvers. And because a molded sail is structurally more efficient than a paneled sail, it holds its designed shape longer than a paneled sail, making the sail more effective over a wider wind range. Put simply, a 3Di sail has a wider sweet spot. This is a significant benefit, for both beginners and experienced sailors alike.
The Unique 3Di Manufacturing Process
Step 1 – Separate the Fibers
The fibers used in sailmaking (carbon, spectra, and aramid) have different structural characteristics, so they are produced as a balanced bundle of fibers we call “tows.” Because 3Di construction allows us to carefully select where each individual fiber goes, we want full control over each individual fiber. So the first step to building a 3Di sail is to separate these tows into custom tapes of each specific fiber. This is done by squeezing the tows over a series of rollers and through a resin bath.
Step 2 – Lay the Tapes
The desired tape of filaments, not yet cured, is loaded onto gantries. The gantry is then directed by computer to follow the “structure” (tape layout) plan, as determined by the sail designer. For example, to create a “clew patch,” the gantry would start from the clew and lay a tape up the leech; then it would return to the clew and lay another tape at a slightly different angle… and continue until it has created a complete section.
Step 3 – Assemble the Sections
The sections of tapes laid down by the gantries are assembled onto the full-scale mold, which has already been programmed to assume the sail’s designed shape. Each section has registration marks, allowing the mold setup administrators to correctly join together all the sections.
Here’s where it gets interesting. Since there has to be some overlap of the sections and extra material in that overlap would create stress risers, we use what’s called a “scarf joint.” The best analogy is tongue and groove flooring. Each section is comprised of multiple layers of tapes (anywhere from a minimum to four, to hundreds), so it’s easy for the pre-programmed gantry file to reduce the number of layers along each joint edge. This ensures that both thickness and modulus (shape holding) are consistent across the entire sail.
Step 4 – Consolidate the Laminate
Just like building a carbon boat, through heat and vacuum pressure the filaments and adhesive become one. Each filament is encased in its own sleeve of adhesive, ensuring both load-absorbing consistency and longevity. 3Di sails do not delaminate!
Step 5 – Curing
The laminate is allowed to cure for about five days before the sail is brought to the sail loft floor for final finishing.