CompositesWorld
Issue link: https://cw.epubxp.com/i/830100
47 CompositesWorld.com orientation from typical ±45° weaves to low angles like ±30°, to meet performance requirements. If a core's density is very low, for example, more structure is required in the skins, which can add weight. Chotikapanich says that skin laminates can be fashioned as sandwich structures of fiberglass or carbon combined with foam, balsa wood, or other core type. e company also offers a range of natural fibers for boards, including banana fiber, coconut husk fiber and flax. Cobra drew on long experience and its in-house database of flexure and breaking-load test results during the Molokai racing board's material selection process. Ultimately, Cobra chose 15.5-kg/m 3 epoxy-compatible, closed-cell expanded polystyrene (EPS) foam, which it manufactures in-house, for the board core. For the board laminate, carbon fiber was the only choice to achieve the lightest weight, while maintaining high stiff- ness without flex, for maximum speed through the water. Cobra selected Sigmatex (Runcorn, UK) sigmaMX ±45° woven biaxial flat, noncrimp carbon fabric, for the board bottom. A Sigmatex 3K carbon plain-weave fabric was used for the deck, because it offered greater impact resistance than the biaxial, notes Chotika- panich. e board rails were "double wrapped," that is, the biaxial on the bottom was brought up over the rail, and the plain weave on top was wrapped over it. en unidirectional carbon fiber tape was applied along the rails. is tripled the carbon thickness to maintain good stiffness over the board's length. A polyvinyl chloride (PVC) sandwich laminate was added to the deck to increase durability and strength in the standing area. A 3-mm-thick sheet of PVC was cut to measure and placed between a layer of fiberglass and the carbon plain weave, after the deck area was cut down by 3 mm to make room for the PVC. And, a smaller 20-cm wide fiberglass- wrapped PVC stringer was placed lengthwise in the nose area, to reduce vibration and flex while the board is under load, explains Chotikapanich: "PVC is much stronger than EPS, but it is heavier, about 80 kg/m 3 , and it adds some cost." Because the sharper tail shape is more suscep- tible to damage, a ply of Innegra high-modulus polypropylene (HMPP) fiber, from Innegra Technologies (Greenville, SC, US), in the tail area helps resist impact damage. e fin box, to which the carbon fiber fin is attached, was reinforced with fiberglass fabric, carbon fiber fabric, PU foam, aluminum and HMMP, to maintain structural integrity in all conditions. Cobra specified Sicomin Epoxy Systems' (Chateauneuf les Martigues, France) trademarked GreenPoxy bio-based resin, currently used in at least half of its board products. Chotikapanich says Cobra's transition to bio-based resin began in 2016, moti- vated by the nature of the recreational board market and Cobra's desire to employ sustainable practices. But, he says, "the resin performance had to be the same as legacy epoxy, and Sicomin has proved that it is — our customers see no difference. We're hoping to use GreenPoxy in 80-90% of our products, going forward." Producing a winning board Cobra produced Grant's race board in a wet layup, vacuum- bagged process, in one shot. (A two-part composite mold was produced following the race for production of boards on demand for NSP, in a vacuum molding process.) Chotikapanich points out the finish on the board, which he calls "unfinished blue," was minimized to save weight: "Rather than painting the entire part, we applied a very light coat, then sanded off some of it, so that the carbon shows through faintly. It would have taken 2 kg of paint to cover the entire board!" Ultimately, the racing SUP, nearly 3 times as long as Grant is tall, weighs only 14.5 kg. Grant points out on social media that he's happy to be winning on factory boards that anyone can buy: "I feel I'm on the best board out there, every time I race." Stand-up Paddleboard Read this article online | short.compositesworld.com/NSP-SUP See the full story of NSP's development of the racing SUP | youtu.be/haQr6HURCoA Visit the NSP Facebook page for more on Travis Grant and other board team athletes | www.facebook.com/ NspSurfAndStandUpPaddleBoards/ Connect with Cobra International at its Web site | www.cobrainter.com Sara Black is a CW senior editor and has served on the CW staff for 19 years. sara@compositesworld.com A winning combination As Grant paddles to the finish line, his winning board's front "rocker" — the slightly higher upturn at the front, which enabled fast gliding — is readily visible. Unseen, but just as important, is its volume — 345 liters — which ensured ample stability during the lengthy ocean race. Source | NSP