In the rarefied world of grand prix racing sails, the distance between first and second can be measured in millimeters.
Today’s racing sails are built out of an exotic menu of high-tech materials using advanced construction techniques to yield shape-specific sails that boast minimal stretch or creep. Here’s an overview of how grand prix racing sails are built, the materials and methods that are involved, and the future of this once-traditional craft.
High-end racing sails are conceived on a computer screen, where a sail designer uses 3D modeling to calculate the optimal flying shape for each sail based on aero elasticity (the balance between aerodynamic pressure and surface tension), detailed rig and hull information, the characteristics of the particular boat, virtual testing and a velocity prediction program. These custom shapes are created using proprietary sail-design software—for example, North Sails’s North Design Suite or Quantum’s iQ software—which runs computational fluid dynamic (CFD) calculations, finite element analysis (FEA) and other performance algorithms, combined with a healthy dose of institutional knowledge and experience. Tolerances are measured in millimeters. With shape being paramount, modern sail design has become a game of carefully applying high-modulus strings, fibers or ribbons to create a “custom fiber map.” Today’s high-end racing sails fall into two basic categories: laminate (aka, “string” or “membrane”) sails and composite sails. While the materials involved can be similar, the construction varies considerably.
Laminate sails are built using a sandwich technique that starts with a film, or scrim, usually made of Mylar. An adhesive (glue or resin) is applied to this film, after which high-modulus fibers of varying lengths and types are laid down in a specific pattern,followed by more adhesive and another piece of film. Examples of laminate racing sails include North Sails’s 3DL (three dimensionally laminated), Quantum’s Fusion technologies, Doyle’s Stratis and UK-Halsey’s Titanium sails.
North Sails’s 3DL sails are built using a construction process in which a number of Mylar panels are first cut and assembled, and an automated gantry is then used to lay down the structural load-bearing fibers. The sail is laminated in one piece with a thermo-setting adhesive on an articulated computer-controlled mold.
In contrast, Quantum laminates its sail in sections, laying a portion of the fiber map on a piece of base film. Excess thermo-set adhesive is removed to prevent excessive brittleness and yield a high strength-to-weight ratio. A top film is then applied, and the sandwich is vacuum-bagged and fused using infrared heat and six to eight tons of pressure, yielding a “cross-linked” molecular structure. Once the laminate sections are complete, they are cut, shaped and joined together to create the complete sail. Shaping is achieved through a traditional technique called broadseaming, in which the sections are joined along a series of curved edges to force draft into the sail.
In the interest of longevity, UK-Halsey builds its laminate Titanium sails using a crosscut construction method that’s reinforced with continuous Kevlar or carbon-fiber tapes running from corner to corner. “Grand prix sails are great,” says UK-Halsey’s Adam Loory, “but most of the market is the average guy who races on the weekends and does a few Thursday nights….These are perfect for Corinthian sailors, who can get three to five years of heavy racing, and after the shape starts to go, they still have another five years of sailing before they die.”
According to UK-Halsey’s Butch Ulmer, Titanium sails are vacuum-bagged and then set in an oven, where heat is applied to both sides of the sail to ensure even activation of the adhesives and to minimize shrinkage. “It’s a meticulous process for achieving good lamination,” Ulmer says.
Over at Doyle Sails, Robbie Doyle says his company’s biggest breakthrough in recent years has been its rapidly evolving use of CFD and FEA. “If you push the limits of fabric, compression forces become important and need to be addressed,” says Doyle. “In order to maintain shape, you need to avoid compression. We’re pushing the envelope with fabrics, but you can’t have any distortion or it all comes tumbling down.”
Interestingly, Doyle has been building laminate sails for Team Sanya, Mike Sanderson’s entry in the 2011-12 Volvo Ocean Race. According to Doyle, Team Sanya will fly a full compliment of Stratis sails, and also will likely supplement these with Doyle’s new “Ice” sails, a technology the loft is keeping close to its vest, at least until full testing is complete. The America’s Cup syndicate Team Korea is also using Ice technology for the Code 0 sails on its AC45 wing-sailed catamaran. In both cases, Doyle has been relying heavily on its CFD and FEA tools to optimize the sails for these two different venues.
At the grand-prix level, where money is no object and winning the only concern, carbon fiber is king due to its “stiffness.” In sailmaker’s parlance, stiffness refers to a material’s ability to resist stretch, which is measured in terms of modulus. “Racing sails are engineered for modulus, not for strength,” says Bill Pearson, technical director of North Sails’ manufacturing plant in Minden, Nevada. “If you have enough modulus to retain your desired aerodynamic shape, in most cases you have an enormous excess of strength.” However, with high-end sails, excess modulus doesn’t translate to improved velocity made good, or VMG. “Interestingly, the carbon used in sailmaking is at the bottom end in terms of modulus of the carbon fiber that’s available,” says David Flynn, director of Quantum Sail’s Special Project Group. “Stronger fiber is available, it’s just more brittle. With increased modulus comes lack of flexibility.”
This brittleness is carbon’s downside. While stiffer, “having a 100 percent carbon sail [means] accepting a sail with less longevity,” says Pearson, who advises that an all-carbon racing sail is essentially a one-season sail. Interestingly, it isn’t sailing hours that cause damage so much as the time the sail spends tightly flaked in its sailbag, stored on the bottom of the boat, or—much worse—getting trampled on.
To increase durability, other materials, including carbon fibers of different modulus, are sometimes used, depending on a sail’s intended purpose. “Below the grand prix tier you see carbon and aramid-hybrid blends,” says Pearson. “As more longevity is required, a higher proportion of aramid is normally found.” Examples of aramid fibers include Kevlar, Twaron and Technora.
In 2009, North Sails unveiled 3Di, its latest technology. Rather than laminating scrims and strings, 3Di sails are constructed using an automated tape-laying head that applies synthetic fibers (currently, aramid/Spectra or carbon/Spectra) in the form of pre-preg filament tapes, each just one filament thick. The robotic head applies many layers of these tapes in an interlocking pattern on an articulated mold, following projected load paths that are calculated by the sail’s designer. These tapes are then vacuum-bagged and heat-laminated, fusing together the fibers to create a “composite” structure, as opposed to a film “sandwich,” in which the straight, untwisted filaments are less prone to moving under load than a bundle of twisted filaments.
The result is an almost sheet metal-like cloth with minimal stretch in any direction.
Flynn, however, disagrees, arguing that there’s minimal weight savings over laminate sails and that while 3Di sails have a “sweet spot” where the sail’s shape perfectly matches the wind velocity, this exactness limits each sail’s effective range. Flynn adds that the sails are expensive, stiff, and no more durable than their competition.
“While promising in some regards, the downsides seem to outweigh the potential gains,” says Flynn, adding that 3Di is an evolution of Cuben Fiber technology, which was developed in 1992 by Bill Koch’s America3 Cup syndicate. “When Quantum looked at the process eight or nine years ago, we decided against pursuing it.”
Propaganda wars aside, the concept of one-piece, sheet metal-like flexible airfoils is certainly forward-thinking. “The new generation of sails—such as 3Di—will not be laminated to films,” says Pearson. “They will be fiber and resin matrix composites, just like masts, race boat hulls or composite airplane wings.”
Future of Sailmaking
“Sailmaking is leaving its textile-based heritage and is now moving fully [into] the composites world,” says Pearson. Future sails, he notes, “are going to be made of the same components as every other maximum-performance structure—carbon fiber and resin, probably with a little Aramid or UHMWPE (Ultra-high-molecular-weight polyethylene fibers like Dyneema and Spectra) for flexibility.”
But this sophistication comes at a price. “Unfortunately, the days of the mom-and-pop loft—or even the independent affiliate of a larger sailmaking group—are probably over,” Flynn says of the grand prix sail business. “It now takes serious resources to create the manufacturing capability, to develop the design tools, and to recruit and train the personnel to build sails at the highest level.”
On the supply end, technologies are developing that will allow sailmakers to realize further advances. “There are exciting technologies in various stages of development,” says Forrest Williams, U.S. brand manager at Bainbridge International, a major materials supplier, “ranging from new approaches to traditional problems like adhesion, substrate preparation, and UV-resistance, to initial forays into experimenting with new materials and technologies—think liquid crystal or Nanotube technology—aimed at increasing interactivity and data exchange between the actual structure of the sail and the trimmer.”
While the America’s Cup is the historic proving grounds for new sail-making technologies, this tradition, too, is changing now that wingsails have replaced soft sails for AC34. But even here, composite technology could be applicable. “3Di is as much a flex-foil as it is a sail,” says Allsopp. “The foil technology potentially leads to possible applications in the America’s Cup—wing-sail surfaces as well as headsails.”