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 sailmakers. During this
period, many of the larger loft organizations were experimenting
with computer aided sail design. Dupont™ 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 Kevlar 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,
sailmakers 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
1
DuPont™ and KEVLAR® are trademarks or registered
trademarks of E.I.du Pont de Nemours and Company.
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