Ships – Sail or control means therefor – Specific sail structure or arrangement
Reexamination Certificate
2001-05-02
2002-05-07
Avila, Stephen (Department: 3617)
Ships
Sail or control means therefor
Specific sail structure or arrangement
C114S102330
Reexamination Certificate
active
06382120
ABSTRACT:
BACKGROUND FOR THE INVENTION
In chronological order in the past century, sails have been made of woven textile materials. Base fibers for these textile materials were derived from natural polymers, i.e., cellulose, of which cotton and linen were preeminent. In general, the fibers in these textile yarns used for weaving sailcloth were of short length as it is typically found in natural polymers. However, significant advantage in sails was realized by longer length fibers and high quality sails were sold as being made of long length “Egyptian cotton” yarns.
With the advent of synthetic fibers, that is an extruded bundle of “continuous” filaments for yarns, the length of fibers in yarns became immaterial, as typically all yarns were a bundle of “mono” filament yarns of substantial “fiber” length. Chopped fiber yams or “spun yams” or “staple” were not used in sailcloth. Hence, the meaning of monofilament yarns, continuous filament fibers, and yarns became interchangeable for sail making purposes. However, besides the “fiber” length in yarns, a synthetic mono filament in a bundle of monofilaments as a yarn possessed many advantages such as initial modulus, tenacity, flex life, elongation at break, elongation resistance, resistance to creep, decay resistance, e.g., ultraviolet and mildew, weight-to-strength ration, etc. etc. These characteristics are for the modern filament yarns superior to the best cotton fabrics.
Accordingly, with the advent of continuous length filaments such as polyester and nylon (a polyamide), sailcloth are made of bundle of continuous filament materials called yarns. Today substantially entirely all sails in economically advanced countries are made of synthetic materials.
As new polymers were developed and as these lent themselves to filament formation and possessed the desirable properties for yarn formation, these materials found increasing use in sail making. For example, Kevlar™ (a polyaramid fiber sold by Dupont Co.) and Tawron™ (a polyaramid fiber sold by Akzo Co.) were used in sailcloth first with indifferent success, but as the fiber properties were improved such use became increasingly prevalent.
As new and improved derivatives of the above materials such as Kevlar 29™ and Kevlar 49™ and PEN polyesters (i.e., polyethylene naphtalate polymer) and entirely new synthetic polymers were developed with properties suitable for sail making, these materials found use in sails, albeit at a very high premium, over conventional polyester fabrics. Examples of such filament materials are: Vectran™ (a polyaramid type of fiber sold by Hoechst-Trevira Corporation), Spectra™, Dyneema™, Certran™ (a high modulus polyolefin filament sold by Allied Corp., DMS Company and Hoechst-Trevira Corporation respectively) and PBO (polyphenylene benzo bisoxazole) sold as Zylon™ by Toyoba Company. A considerable effort has also been expended to develop carbon fibers for sail making use, e.g., carbon fibers coated with a polyester or a polyamide polymer. Recently, macroscopic fibers and ribbons of oriented carbon nanotubes have been disclosed having excellent flexibility character (cf.
Science
, Vol. 290, Nov. 17, 2000, pp. 1331-1334.
In sail making, when evaluating the above and novel filaments, the following tests are used:
Initial modulus: a measure of the yarn's ability to resist stretch. It indicates how well the filaments will hold shape, and is measured in grams of load per unit of stretch for a given denier. The higher the number, the less the stretch. Also defined as the slope of the initial straight portion of the stress-strain curve.
Tenacity: The yarn's initial breaking strength, expressed in grams of force per denier. This is a good measure of a filaments ultimate strength. The higher the number, the more load it takes to break the filaments.
Flex life: A measure of the filament's ability to retain its strength after being folded back and forth. It is expressed as a percentage of the fabric's strength lost after 60 bend cycles.
UV resistance: Expressed as the amount of time it takes for a yarn to lose 50 percent of its modulus; normally conducted with artificial UV exposure.
Elongation to break: A measure of the filament's ability to resist shock loads. It is measured as how much such filaments will stretch (as a percentage of its overall length) before it breaks.
However, despite the advances in synthetic polymer technology, the inherent shortcomings associated with woven technology are evident, i.e., 90 degree warp and fill orientation and the over and under shape of the warp yarns caused by weaving called “crimp.” These inherent shortcomings cause considerable problems associated with sail shape distortion. Shape distortion is caused by the anisotropic properties of the material when the force is applied at less than 90 degrees to the fill and/or warp orientation. It should be noted that typically sailcloth was woven with the better properties in the fill direction as the warp yarns, because of the “crimp” in the yarns, did not have the same elongation characteristics as the fill yarns. To remedy the inferior warp direction properties, “warp inserted” fabrics were also produced.
Within about the last 25 years considerable effort has been devoted to address the bias distortion in sails arising from the conventionally woven fabrics. This effort has had a three-prong approach. First, sailcloth manufacturers sought to improve the sailcloth by resin and heat treatment and resin applications. Additionally, sailcloth manufacturers added laminated films, typically a polyester film to the fabric on one, both sides, or in between two fabric layers. As the second approach, the sail makers employed panel orientation to align the fill threads or yarns with the load path, e.g., in tri-radial sails to minimize the bias inherent in a triangular sail typically used on recreational sailboats. Finally, as a third approach, sail makers devised structural sails (also known as fiber- or yarn-oriented sails) for racing; these were real “breakthrough” sails.
For structural sails, the initial development was to place the structure in the form of fabric strips, bundled monofilament fibers, i.e., yarns or yarns in the form of tapes on the skin or membrane of the sail. These added structures followed the load path in the sail. The load or stress maps for a sail had been available to sail makers for a number of years. The whole structure was typically confined either on one side or the other side or both sides of the sail. A subsequent development confined the structure between two layers of a film.
Bias distortion as used in the sailing parlance is typically caused by a load (also force or stress) that is “off-the-thread line.” That is, if the warp (or ends) and the fill (or weft) yarns are in a line with the major, predominant load, sails are said to have the stress “on-the-thread” line,” i.e., be less bias distorted. Typically, a sailcloth is woven with the fill threads under tension and therefore these do not suffer from the “crimp” of the warp threads. These fill threads are not as much subject to elongation as the warp threads when the sail is under load. However, in a typical sail there are other loads or forces “off-the-thread” line. By adding a laminated film to the material, typically a polyester film or a poly vinyledene chloride film (e.g. sold under a trademarks Mylar or Tedlar, respectively, and produced by a DuPont Company), bias distortion was reduced because these films display substantially isotropic properties. Improved polyester films such as PEN, (which is a polyethylene naphthalate polymer, i.e., a type of polyester polymer), may also be used in a film form and is also available as a yarn. Composite films of more than one polymer may also be used such as disclosed in U.S. Pat. No. 5,221,569. As previously mentioned, the yarns in prior art fabrics may be substantially immobilized by hot calendaring, resin impregnation, resin coating, as well as the laminating with the above-mentioned films. Reduced anisotropic characteristics are thus obtained. Neve
Avila Stephen
Keire Fred A.
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