| 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.
 Closeup of 3DL laminate shows laminate films tightly conforming to structural yarn with a minimum of voids.© North Sails
“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.
 © North Sails“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. |