by
Peter Mahr and Brian Doyle
Almost every piece of modern sailcloth begins life as an industrial
fiber. While the brand names of many of these fibers are well known to
sailors, their basic properties are less well understood. The characteristics
of these fibers are an important factor to consider when choosing sails
for your boat. Over the past few years there have been some significant
developments in high performance fibers that have applications in sailcloth.
The result is a greater variety of options for performance sailcloth makers
and their customers, allowing them to select the blend of performance,
durability and cost that best suits their needs.
Polyester
Polyester is today's "classic" sailcloth fiber. It
is often called by the Dupont trade name DACRON® although there are
other suppliers of polyester yarn used in sailcloth. Polyester is widely
used for its combination of reasonably low stretch, good strength, low
cost and durability. Because it can be heated and shrunk during weaving
to form a tight, stable woven cloth, polyester woven sailcloth remains
a good choice for cruising sails and certain racing sails. Polyester is
available in many types. Dupont’s Type 52 is a "high-tenacity"
premium fiber offering a balance of higher strength, lower stretch and
maximum shrinkage. Other premium polyesters, with comparably excellent
properties at more attractive prices, are now available from Asian and
European suppliers. Their use in sailcloth has increased over the last
few years at the expense of Dacron.
Nylon
Nylon is used for most downwind sails because it is strong and
light. Nylon is relatively stretchy, allowing it to absorb shock loads
and making it easier to fly and more stable in wavy seas than a polyester
material would be. Dying this fiber is easier than any other and it is
often available in a variety of colors.
Aramids
A popular class of high performance fiber in laminated sailcloth
is the Aramids. The most well known aramids are Kevlar™ (a Dupont
trademark) and Twaron™ (made by Teijin/Twaron of Japan). Sails made
with aramid fiber are lighter than woven Dacron or Polyester laminates,
and have greater effective wind ranges. The tradeoff is higher cost and
shorter sail life. The stiffer Aramid fiber is more susceptible to sunlight
(UV) damage and breakdown due to folding and flogging.
Aramids are produced in a number of different styles, with different balances
of stretch, flex strength, weight and cost. High modulus (low stretch)
types such as Kevlar 49 and Twaron 2200 are the most appropriate choice
for racing sails. A variation of Kevlar called “Edge” was
promoted a couple of years ago because it had slightly higher initial
modulus. North’s testing revealed that this effect disappeared almost
immediately with use. This type has since been discontinued.
Another aramid fiber is Technora, which is similar to medium modulus Kevlar
in chemistry and performance. Initially it has a bit higher strength but
loses strength more rapidly in UV making it similar in durability in most
applications. It is commonly seen with a black coating, which is intended
to provide some UV screening.
Vectran
Vectran is a LCP (liquid crystal polymer) fiber sold by Hoechst.
Vectran’s stretch resistance is nearly as high as a standard modulus
aramid, and it is somewhat stronger when new. It differs from aramids
in its chemistry and has somewhat better flex resistance as long as it
is shielded well from UV. Under UV exposure, it degrades more rapidly
than aramids and far faster than Spectra/Dyneema.
Carbon Fiber
First used successfully in the 1992 America's Cup, carbon fiber
laminates provide exceptionally low stretch and light weight at the expense
of higher cost and somewhat shorter life span compared to an aramid sail.
Careful R+D and on the water testing is critical with this fiber. Carbon
is available in a wide variety of types, only a few of which can tolerate
the flexing seen in normal sail use. Laminating techniques are also very
critical to get the available high performance as well as to achieve the
best possible durability. Experience over that last few years on top boats
with 3DL carbon and carbon/aramid sails has been very positive and the
fiber is seeing increasing use by more types of boats.
Spectra/Dyneema*
Spectra, and its European counterpart Dyneema, offer even lower
stretch, higher strength, better UV resistance and much less strength
loss in flex than Kevlar. However, Spectra/Dyneema sails stretch (creep)
under long-term load, which makes them unacceptable for racing sails.
After considerable development, this fiber is now used with excellent
results in sails for large performance cruising boats.
* Note: We use the somewhat awkward ‘Spectra/Dyneema’ reference since we employ the two fibers almost interchangeably and sometimes in the same piece of cloth
PBO
At the top of the theoretical performance list is PBO, a fiber
made by Japanese company Toyobo. This fiber has been used for a number
of years in both 3DL and paneled sails. It has proven to be somewhat better
than an aramid sail in performance when new but degrades rapidly under
the combination of UV and flex. Because it is a very expensive fiber,
its use in sails has all but disappeared in favor of the even higher performance
and more durable carbon option.
PEN
PEN is a fiber with stretch between polyester and aramid and
with slightly higher strength than polyester but far less than aramid.
That combination and a cost approaching aramid have meant that this fiber
has limited application in sails. It has been ruled to be polyester and
as such can be used in one-design classes that limit their sails to polyester.
Summary
New fibers continue to come out of the labs. Some will become
standards while others will disappear. Despite the promise of these exciting
new fibers, design still plays a vital part in their successful application
in your sails. Simply inserting a spicy new fiber in a poorly engineered
fabric or sail design is a formula for failure. Similarly, enough of the
fiber must be used to handle the sailing loads and the abuse it will take
in tacking, flogging and handling. Low stretch has always been desirable
in selecting fibers for sailcloth but this is only one element in a sail's
performance. It is ultimately the combination of fiber, fabric and sail
design that makes for a winning sail.
Fortunately for North our 3DL molded sailmaking process allows us to produce a test sail from a new fiber within a few days of its arrival at our factory in Nevada. This has allowed us to quickly evaluate new offerings and to remain the industry’s technological leader.
