Enclosed is an edited version of a research
paper on sail material strength that was originally
written by Kyle McMillan, a young sailor who
is currently a high school senior in Delaware.
Kyle originally contacted me last fall for a
PolySail sample to use for her senior research
project. I agreed to send her a kit and provide
some suggestions for research if she would put
me in touch with her instructor to validate
the project assignment and agree to send me
a copy of her final paper.
In the course of our email correspondence,
Kyle laid out her research plan for testing
the strengths of various sail materials. It
soon became clear to me that she had access
to some very sophisticated testing equipment;
and that if her original experimental research
went well, the results might be of great interest
to all the sailing community. Subsequently,
I offered to see if I could get her results
published if she did a respectable job on her
project. When I received her final report, I
was greatly impressed both with the quality
of Kyle's writing and with the level of original
research. I think you and your readers will
also be impressed when you check out this edited
version of her report.
While my product did not fare well in the final
testing, I don't think this report diminishes
polytarp as an inexpensive alternative to other
sail materials as long as the polytarp sails
are well cared for. In fact, I was surprised
at our material's performance in the initial
strength testing against some of the better
known sail products. In the end, as both a businessman
and a part-time writing instructor at a local
community college, I think I received exceptional
value for my time and material investment in
I also learned something about the ultimate
strength of our PolySail material and have now
begun offering many of our kits and custom made
sails in an 8 oz. vs. the 5.5-6.0 oz./sq. yd.
material we carried exclusively before. At some
point, I hope to be able to convince Kyle to
do a retest that involves this heavier polytarp
material, a little less grueling UV-moisture
testing, and some lower end competitive products,
such as Tyvek. At the same time, I can see where
you, I, and others might be interested in the
sail applications of the Tenera material and
thread. Wow, that is one tough fabric and material!
I'm thinking America's Cup sail quality--and
Highest regards, as always,
of Ultra Violet Light and Moisture
on the Strength of Sail Materials
By Kyle McMillan
As a young sailor, I have always been
advised by my elders to follow certain procedures
in caring for my sails when I return from a day of
sailing.. “Lay out your sails. Wipe off the
dirt and moisture. Flake and roll your sail tightly
and carefully. Make certain you keep the sail in its
bag. Put the sail away in the shed.” Experienced
sailors seemed to feel that the least amounts of dirt,
saltwater, rainwater, or excessive sunlight could
damage their sails and hinder their boat’s performance.
Back in the days of canvas and cotton, I thought,
the perceptions of these “old salts” were
probably true. But what about modern sail fabrics
and technologies? Weren’t Kevlar sails and other
modern laminates practically bulletproof? Did I still
have to baby my sails? These were some of the questions
I set out to answer in this paper..
To begin my quest for answers, I needed
to know more about the development of sail fabrics;
so I turned first to history and the experts. “In
the past, sails had to be constructed from whatever
materials were at hand, such as skins, flax, cotton,
bamboo, coconut fiber, and jute. Whatever the material,
all sails suffered from stretch and shrinkage, and
most let the air seep through” (Bond, 1990).
Next came cotton. “Cotton, being a natural fiber,
has poor resistance to rot, UV light and water absorption,
hence the coating of sailcloth with varnish, making
the sails quite heavy and stiff. These qualities made
it unsuitable sailcloth” (John, 2004). In 1902,
Ernest A. Ratsey came from England to America and
introduced Egyptian cotton. Although this cotton stretched
less, it experienced problems with moisture, rot,
and mildew. Nylon, which took its name from New York
and London, eventually appeared as the first synthetic
fiber; but, the early versions of Nylon used in sail
making had problems with ripping, elongation, and
water absorption. Sailmakers tried Orlon next; but
since it could only be woven into lightweight cloth,
its application was limited to small One Design [boats]
(Whidden and Levitt, 1990). Dacron®, another synthetic
created as a by-product of oil refining, was invented
in 1941 and is now owned and trademarked by the DuPont
Company. However, it was this polyester fiber that
created the initial competition between the two lead
sail manufacturers, Ted Hood of Hood Sails and Lowell
North of North Sails, Inc. Their competition to improve
sail fabrics eventually revolutionized the sport.
In the latter half of the Twentieth
Century, improvements in design, strength, longevity,
and stretch resistance, started occurring all over
with smaller companies now joining the competition
and making use of newly developed sail materials.
The most important fabrics today include Dacron®,
woven Nylon, Polyester/Mylar laminates, Kevlar®/Mylar
laminates, and Spectra/Mylar laminates. “Prior
to laminated sailcloth…the most desirable qualities
for sails— lightweight, low stretch, high strength,
and durability— could not be combined in one
package. Low stretch meant heavy; lightweight meant
delicate.” (Whidden and Levitt, 1990). Sailors
and sail manufacturers now tend to look more closely
at the fabrics and how they move, testing every possible
To create a successful sail, manufacturers
have to test for certain properties that may reveal
weaknesses in their sail fabric. The cloth’s
geometry, stretch resistance, strength, weight, flexibility,
tenacity, porosity, water absorption, and ultraviolet
(UV) resistance might all be tested. For example,
Haarsticksails, Co., a sail manufacturing company,
first measures initial strength, or maximum weight
capability, on an Instron machine, which pulls a strip
of material until it tears. Next, the same fabric
is placed in a unique Impact Flutter machine, which
is essentially a wheel that spins the strip causing
it to forcefully hit the side of a wooden table. Company
personnel then re-test the strip for strength in the
Instron machine and compare the two results as a simulation
of how well a sail may hold its shape on a boat. “These
days, few sails actually fail by breaking, but many
are flown in more wind than they are designed for
and fail by becoming permanently distorted or blown
out” (Whidden and Levitt, 1990). By determining
the material’s yield strength, which is the
point beyond which it can no longer recover to its
original length, having exceeded maximum load capability,
and comparing it to the predicted sail-load that may
be experienced, companies can estimate a maximum wind-speed
potential for a particular piece of fabric.
However, I was more interested in learning
how well modern sail materials held up to sunlight
and moisture. Did the old timers’ advice still
hold? If a sail material comes in contact with UV
rays and moisture, will its strength gradually decrease,
making it more susceptible to tearing?
For my test, I was going to need three
essentials: 1) some modern laminated sail fabrics,
2) an Instron machine to measure fabric tear strength,
and 3) a machine that could “weather”
a sail fabric with UV exposure and moisture. I chose
ten different sail materials representing a wide range
of prices and (advertised) quality, including: DuPont™
Sorona, PolySail International’s PolySail material,
DuPont™ Dacron®, North NLT 605XI5 6000 DPI,
Dimension-Polyant FLX08A, Contender AKS6, Bainbridge
CL75, Bainbridge Ocean745, Bainbridge DIAX2 70TT,
and two strips of WL Gore & Associates’
architectural fabric, TENERA, a new architectural
fabric that has incredible resistance to moisture
and UV exposure. WL Gore & Associates’ Instron
Tensile Tester 3360 Series, Dual Column Testing, was
made available to measure tensile strength/breaking
force, which is the load, in lbs/inch, at which the
material tore. WL Gore & Associates also provided
their QUV Accelerated Weathering Tester to weather
the sails with ultraviolet light and moisture for
retesting in the Instron machine later. By comparing
the initial and “weathered” points at
which the fabrics tore, I expected to learn whether
our modern laminated sail fabrics still needed all
the care that mature sailors recommended.
To measure the tensile strength of
the fabrics, I cut each sample into five 1”
x 14” separate strips. The first four strips
were used in the Instron machine to measure the initial
“breaking point” of each of the fabrics
in pounds per square inch. The results of these tests
appear in Figure 1 below.
Figure 1 (Note: Test results
are +/- 20 lbs. )
The fifth sample of each type of material
went into the QUV Machine on November 22, 2006. Each
day this machine emitted 20 hours of UV light intensity
and produced a four hour condensation cycle in which
the air inside reached 100% relative humidity then
condensed on and soaked the fabrics. After 65 days
of this intense treatment, I photographed and recorded
observations about the “weathered” fabrics
recovered from the QUV machine. Finally, I removed
the surviving sample strips and sent them back to
the Instron machine for final strength measurements.
The pictures below show the results of this intensive
weathering. The table below the picture reflects my
||Visible Observations Post-UV
|Not as soft. Discoloration.
|Torn across the middle. Very dry.
|Discoloration. Stiff. Curling under from the
|Coating is peeling and chipping off. Stiff
|Lost all color. Shrunk. Very fragile.
|Discoloration. Sides are curling under. Stiff
|Little change except stiff and some wrinkling.
|Coating is coming off.Stiff.
|Coating is coming off and has air bubbles. Stiff.
|Some stiffness. Discoloration.
|No visible changes.
As the table makes clear, only the TENERA fabric
showed no visible changes and still felt the same,
having an average initial strength of 502.5 lbs/in.
The TENERA fabric is (barely) visible at the top of
the photo above.
Finally, all fabrics, except for the nylon ripstop
and PolySail material both of which had deteriorated
too much to test, were re-tested on the Instron for
its post-UV and moisture strength. The results appear
in the following chart:
The results of this experiment appear to justify
experienced sailors’ concern for sail care.
Nearly all the sail fabrics weakened and deteriorated
substantially after intense exposure to UV and moisture.
Only the TENERA archtechtural fabric, which is not
currently used as a sail fabric because of its thickness,
weight, and expense, showed no deterioration. In fact,
a couple of my samples surprised me with the amount
of deterioration they suffered. The ripstop nylon
practically crumbled in my hand after the UV/moisture
testing. In addition, I showed the Post-UV PolySail
sample to David Gray, who markets sailmaking kits
made from the PolySail material, and he was shocked
at the extent to which his material had failed. He
emailed this response:
the reasons that the polyethylene and ripstop nylon
materials failed so miserably in this test could
have something to do with the thickness and/or weight
of the materials being compared. The 5.5 oz. /sq.
yd. white Polytarp, might look pretty good compared
to 2.5 oz. blue Polytarp under the same conditions.
From experience in using both materials as boat
covers, I know that the blue tarps disintegrate
much faster than the white ones under harsh winter
conditions. Ripstop nylon is also a very thin, lightweight
synthetic which might account for its poor performance
under the UV/moisture test. D. Gray, of Polysails
(Personal Communication, January 26, 2007).
The fabrics with the clear coating on them, like
the Contender AKS6 and the Dimension- Polyant fabrics
seemed to have more resistance to strength loss during
Although my experiment tested multiple variables,
there were many more variables that I could have tested.
If I were to run my tests again, one thing I would
certainly do would be to make certain that all fabrics
weighed the same. I would also test these samples
for more properties to figure out their overall efficiency.
That way, I could compare one fabric’s overall
performance level to another. A second test might
also explore the economics of sail materials to see
if less efficient ones are being sold for higher prices.
The results could be released to customers as more
information for making the smarter buy.
After talking with David Gray about his PolySails,
I also learned that the color of a fabric can make
a difference in its resistance to UV light. Using
that knowledge, I would like to conduct another similar
test using only one color for different fabrics. Another
alteration I would make in a future experiment would
be to test each sample in more than one direction.
Each fabric has multiple types of fibers running in
separate directions, whether in warp, fill, or bias.
By testing all three directions, I would most likely
get three strength measurements that differ considerably.
A three-direction test would be a much more reliable
test of overall strength because the sail has to hold
shape and strength in every way possible.
For maximum performance, a sailor selects the sail
for his or her boat depending on how it will be used.
Manufacturers sell cruiser sails, racing sails, spinnakers,
etc. In another test, I would use only one type of
sail. If more variables were controlled, the results
could have been much more significant and valuable
to both manufacturers and sailors.
The results of this experiment made me realize how
much I am harming my sail by leaving it out in the
sun too much. Also, after seeing the extent of Nylon’s
degradation due to moisture, I am going to start wrapping
up my sail even tighter and putting a cover on it
in the shed in order to help protect the fabric from
mold, moisture, and all light. “Treat your sails
like a newborn baby, and you will sail faster and
extend their life. A little tender, loving care goes
a long way” (eHow, 2000). I guess I have to
concede that the “old salts” were right.
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