SAIL TECHNOLOGY
Sailcloth and Sail Design
- Hand in Hand
Laminate sailcloth has evolved on a parallel path
with sail design. In 1980 polyester laminates (commonly
called Mylar sailcloth) became commercially available
to sail makers. During this period, many of the
larger loft organizations were experimenting with
computer aided sail design. Kevlar laminates were
also available at this time but they were produced
using small denier Kevlar 29 fibers used in woven
"taffetas" laminated to Mylar film. The small denier
Kevlar fibers were brittle, susceptible to the sun's
UV rays, did not like to be folded or bent, and
were easily mutilated. Other cloth manufactures
also produced Kevlar 29 laminates during this era,
but customer complaints continued about fragile,
expensive sails. The term "exotic" was used to depict
the high cost and short life span of these sails.
In 1986 Dimension Sailcloth (DP) introduced "Interply",
the first laminated sailcloth to use inserted, unwoven
ribbons of fabric. The larger denier Kevlar yarns
were less prone to failure caused by UV and flex,
and the fabric was significantly less expensive.
Interply was improved upon by using a formed scrim,
which creates fabric that is not only strong in
the warp direction, but also in the fill. Formed
scrim is now the basis for all premium laminates
produced by the world's sailcloth manufacturers.
In 1992, probably the biggest milestone in cloth
technology happened. DP introduced Technora, a Japanese
aramid similar to Kevlar 29, in an attempt to increase
sail durability. Technora displays some attractive
properties such as moderately better flex resistance.
Technora took the industry by surprise not because
it was that much better than Kevlar 29 but because
it opened the field for new fibers. DuPont soon
after released Kevlar 49 to the sailcloth manufacturers.
Kevlar 49 is about 30% more stretch resistant than
K-29 and marked a significant improvement in low
stretch, lighter weight sails. Soon other fibers
became available such as PBO, Twaron, Spectra, Vectran,
Pentex, and others. The major cloth manufactures,
Contender, Dimension, and Bainbridge, now have available
a wide selection of fibers and can select the best
fiber for the job. You now see laminates, for example,
with Kevlar 49 for the warp, Kevlar 129 or Vectran
for the fill and Spectra or Technora for the X ply.
The laminating process has also improved dramatically
since the first "plastic sails" were introduced
so failure due to poor lamination is essentially
a thing of the past. The cost and life expectancy
of today's laminates do not constitute the term
"exotic". For club to grand prix racing, laminates
are the rule rather than the exception.
With the introduction of warp oriented laminated
sailcloth, sail makers began the construction of
"radial sails" where the panels radiate out of the
three corners of the sail. This was done to align
the strongest fibers with the primary loads or stress
on the cloth. Radial construction would not have
been possible without the computerization that took
place in the early eighties. Imagine trying to draw
and cut all those triangles with the desired shape
without the aid of a computer.
Today, sail designers are using aerodynamics and
structural computations more than ever. When designing
a sail, the flying shape must be correct for the
aerodynamic pressures. The panel layout is adjusted
to insure the stress on the sail aligns with the
orientation of fiber in the laminate. Using both
a stress and aerodynamics program, a sail designer
now can simultaneously change the shape with regard
to pressure and change pressure to check the effects
on the shape. A graphic representation of load on
the different areas of the sail helps determine
the type of fabric needed, corner reinforcement
size, and even batten length and stiffness. In addition,
sail designers using velocity prediction programs
are now optimizing sail shape for specific hull's
lift, drag and heeling moments. A fast sail needs
entry angles that exactly match the oncoming flow.
These tools and improved fabric allow the sail designer
to design a highly efficient sail with the optimum
weight Vs strength. Paneled sails are now the lightest
and strongest sails available.
Special thanks to: Greg Jarvis National
Sales Manager for Contender Sailcloth and
Rich McGee VP for Dimension Polyant
|
|
Fort Walton Beach