|
II. LAMINATED SAILCLOTH
Laminated sailcloth first appeared in the 1970s and 80s and changed the world of sailmaking, starting with the high performance racers of the America’s Cup and, over time, working down to the performance cruisers at the local yacht club.
|
The reason for the eruption and continued growth of laminated sailcloth is threefold:
- Lamination is the most effective method of combining materials with different characteristics to maximize the advantages of each.
- Films such as Mylar® and PEN are extremely efficient in reducing stretch in all directions which is particularly useful in the “off threadline” directions.
- Laminates allow fibers to be placed in a straight, uninterrupted path, which results in the most efficient utilization.
|
| Photo courtesy of Contender Sailcloth |
|
There are as many, if not more, variations of laminated sailcloth as there are of woven sailcloth, but there are four main construction styles worth noting.
Type I: Woven/Film/Woven or Woven/Film
 |
|
Picture courtesy of
Dimension-Polyant Sailcloth
|
Woven material on one or both sides of film is used in both very inexpensive cruising fabric as well as some of the high-end fabrics. Lower-end versions of this construction consist of a loosely woven Dacron taffeta laminated to a layer
of film. In this application, the film provides most of the stretch resistance and the taffeta is mainly utilized to enhance tear and abrasion resistance. The high-end version of this construction utilizes a woven Spectra or Kevlar taffeta laminated to a
film layer. The high-modulus woven fibers provide the threadline stretch resistance and the film controls the off threadline stretch. In some newer styles, off threadline reinforcing yarns, usually Spectra® or Technora®, are laid into the laminate. This is a relatively cost and weight efficient method of producing a laminate. Due to the crimp in the woven yarns, such laminates are inherently more stretchy than those produced with a core of inserted warp yarns or a scrim.
Type II: Film/Scrim/Film or Film/Insert/Film (a.k.a. “Film-on-Film”)
 |
|
Picture courtesy of
Dimension-Polyant Sailcloth
|
In this construction, the structural fibers (either in scrim or insert form) are sandwiched between two sheets of film. This way, the load-bearing members are laid straight and, unlike wovens, there is no crimp. This takes full
advantage of the fiber’s high modulus in resisting stretch. Additionally, laminating film to film creates a very strong and dependable bond that allows a minimum amount of glue to be utilized.
Although Kevlar is the most common structural fiber used in this construction, Pentex is growing in popularity, particularly in classes where aramids and other exotics are prohibited. This is also the laminate type used for most carbon
fiber sailcloth, and for the Doyle D4 sails.
Unfortunately, film is not as abrasion or flex resistant as a woven and does not protect the structural fibers from harmful UV rays. Because of this, material of this construction is only suitable for short-lived racing sails in which
minimum stretch and weight are the primary goals. In some sails, a UV film is added to protect the core fibers from degradation. In other instances, where additional durability is desired, a taffeta is added to one side to reduce breakdown from flex and
increase abrasion resistance. This style is very popular with PHRF sailors who need performance plus the value of durability.
Type III: Woven/Film/Scrim/Film/Woven
 |
|
Picture courtesy of
Dimension-Polyant Sailcloth
|
Laminating a woven material (taffeta) onto both sides of an oriented scrim takes advantage of the straight yarn principle and the film-to-film bonding. In addition, the taffetas protect the film from both flex fatigue and abrasion
and protect the core fibers from UV degradation. The core fibers include polyester, Spectra®, Kevlar®, Pentex® and most recently Vectran®. In many cases one fiber is used in one direction with another at 90 degrees to it and at times even a third is
added at an angle to provide off threadline support. The taffeta can either be a lightweight polyester or a woven Spectra® or Kevlar®. One might think that having a high modulus core plus a high modulus woven taffeta would result in the ultimate
fabric. However, although there are advantages, the efficiency of the straight yarns in the core is so great that they control and dominate the stretch characteristics of the fabric, and even a high modulus taffeta adds little to the overall stretch
resistance. Such fabric is therefore inefficient in terms of cost and weight. In some special applications such as Around Alone races, Kevlar inserted fabrics with Spectra taffetas are used. In these styles, the Kevlar controls the stretch and the
Spectra supplies the abrasion resistance so that each fiber is doing what it does best and, though expensive, the fabric meets its design goals.
This is a very attractive construction when utilizing high modulus fibers that have superior yarn qualities in every respect expect for UV resistance. As long as the UV-sensitive fiber is in the interior, it remains protected from UV
exposure. For heavier weight styles, extra layers of structural fiber separated by film are often added, creating a multi-ply laminate particularly suited for the high load applications of the megayacht market.
Type IV: Woven/Scrim/Woven
 |
|
Picture courtesy of
Dimension-Polyant Sailcloth
|
Wovens on both sides of a scrim with no film is an enticing construction method in that it eliminates the film layer. The dilemma with this type of construction has been getting enough high modulus yarn into the sandwich, and still
being able to get a satisfactory bond. Bonding two woven fabrics to each other is not easy and adding inserted yarns in the middle makes bonding even more difficult. Controlling the off threadline stretch has also been a problem. However, research
and development continues on this front as the drawbacks of film become evident in many of the megayacht sails in which durability and a long working life are key.
III. SPECIALTY SAILCLOTH
Cuben Fiber
A specialty Spectra laminate sailcloth produced by the company of the same name, Cuben Fiber laminates use unidirectional prepreg tapes of in-line plasma treated Allied Signal’s Spectra 2000 fibers spread to mono-filament level films. The Cuben Fiber process
involves neither twisted filaments nor weaves and reduces “creep” and “crimp” to levels undetectable with standard sailmakers testing equipment. The result is excellent sail shape holding. Sails made with Cuben Fiber are also significantly
lighter and thinner than similarly performing substitutes. Although the jury is still out on Cuben Fiber, physical shrinkage is widely believed to be a problem. Also problematic is the often prohibitive cost of these high tech sails for all but the most
well funded programs.
In summary, laminates are gaining popularity in building everything from boats to planes, primarily because it is proving to be the most efficient way to utilize the latest materials. However, multi-layered materials that rely on glue for
structural stability constantly battle delamination of the various layers. Also, although all sails mildew, it has proven much trickier to remove mildew between laminate layers than on the surface of Dacron sails. Although new chemicals have been
produced that make this possible, there is an added time and monetary investment.
For a more in-depth look at construction methods, fibers and sailcloth samples, please contact your
local Doyle loft.
|
