Under the 3DL Microscope
Bill Pearson is the Technical Director at North’s 3DL®
manufacturing plant in Minden, Nevada. In his role as product manager for 3DL, Pearson, a sailmaker with a technical bent, also functions as a “translator” between the six full-time 3DL engineers and North sailmakers and salespeople. With Pearson and 3DL, there’s always something new.
“Recently I studied a number of 3DL sail samples under an electron scanning microscope to see exactly how the 3DL laminate compares with that of ‘look-alike’ sails that are laminated in flat sections before being assembled into a sail. What we found is that because many of the ‘look-alike’ sail laminates are formed with little to no vacuum pressure, there are a lot of voids in the laminate. The microscope showed that 3DL laminates are continuous adhesive and fiber (above), but in some ‘look-alike’ laminates there are a lot of voids—places where the adhesive is missing, places where there is air where there should be fiber or film. This is a sure sign of an inferior bond that will not stay together nearly as well as a laminate that is formed of continuous fiber and film.
“Another thing the microscope revealed was the difference between forming a laminate using vacuum pressure, which is how 3DL is made, and forming a laminate using pressure from rollers, which is how a few of the typical ‘look-alike’ sails are made. 3DL sail material is built using one atmosphere of vacuum pressure, which is about 1,800 lbs per square foot. Some ‘look-alike’ sail laminate material is built by feeding flat sheets of film and fiber through rollers, which compress everything together without any vacuum pressure. The difference is that 3DL uses the effect of vacuum pressure, together with the heat-curing process, to in effect ‘shrink wrap’ the film around the individual yarns. We call this ‘consolidating the laminate,’ because the vacuum is applied between the layers and sucks the films down and around the yarns, resulting in a laminate of solid film and fiber. But if you try to laminate sail material just by using external pressure, which is how most ‘look-alike’ sail material is built, no matter how much pressure is used a roller can’t crush the film down in between and around each yarn—there will always be voids in the material.
“Traditional laminated sailcloth for use in paneled sails is made using a nip roller system, which works fine, so why would it be less effective in ‘look-alike’ sails? The answer lies in symmetry and profile. With a laminated sailcloth, the yarn or fabric is symmetrical, with a number of yarns per inch, all running the same direction, and the pattern is repeated across the width of the roll. The idea behind both 3DL and the ‘look-alikes’ is that you have greater fiber concentrations where the loads are, and less fiber elsewhere where you don’t need it, so that it is a more efficient usage of fiber. This creates bundles of fibers concentrated in high-load areas, so you don’t have an even laminate thickness. In addition, load-oriented sails have fibers running in a multiplicity of directions, not all running down the length of the fabric, like in sailcloth. Thus a lot of fibers cross over other fibers, making it even more difficult for a roller to press film down into spaces that are only millimeters between fibers. That’s why we use vacuum pressure to build 3DL sails.
“I also discovered that the fibers of a typical ‘look-alike’ sail are impregnated with resin, which we have found is the wrong way to build a flexible laminate. It’s far better, in terms of sail longevity, to coat the fibers with resin rather than impregnate them. This is because resin impregnation of fibers, which a boatbuilder does when laminating a fiberglass, carbon, or aramid hull or deck, produces a composite with fibers that are rigid. This makes them far more rigid when they flex. When building a composite airplane wing or a boat hull, resin impregnation is necessary. But when building sail material, resin-coating the fibers is the right way to go, because we are building a composite laminate that has to be flexible. Resin-coating allows the outside of the fibers to adhere to the 3DL film while giving the inner yarns of the fiber bundle some freedom to move and align themselves—instead of break—when the sail flexes.