There’s a fair amount to be considered choosing one high modulus fiber over another for running rigging. I’ve copied some descriptions that were part of a study looking at the compatibility of various ropes for static load lifting in a mountaineering environment:
Kevlar: Kevlar was one of the first high-strength fibers to be used in rope. It still offers high tensile strength and very low elongation, but has poor fatigue properties. The fibers inside the rope abrade each other, offering little indication of the reduced strength until the rope breaks. Kevlar has a very high melting point, 500 °C or 932 °F. Kevlar-core ropes are sold as escape lines for firefighters - to be used once and discarded. Manufacturers have had some success at solving the self-abrasion problem by combining Kevlar with Spectra. Technora: Technora, like Kevlar, is an aramid, but with vastly improved fatigue properties. It shares Kevlar's high tensile strength and high melting point. Spectra: Spectra is a very high molecular density form of polyethylene - the same thing used to make grocery bags, six-pack carriers and milk jugs. The manufacturing process aligns the molecules, which vastly increases the strength of the material. It is twice as strong as hardened steel (per unit area) and one-tenth the density. Spectra has several difficult issues. The melting point is very low, 147 °C or 297 °F, not much warmer than boiling water. The material is unbelievably slippery, which makes it difficult for manufacturers to form into a workable rope. And, while the modulus of the fibers is comparable to steel, they slowly elongate under a continuous load. This process is called "creep." It is mostly irrelevant to climbers, but annoying to sailors. Spectra/Nylon is also known as Dyneema (a trade name of Beal Ropes) in Europe. Vectran: Vectran is a liquid crystal polymer - its properties are between those of crystalline solids and liquids. It has similar strength to Spectra, but without the creep problems. It has poor UV resistance, which is not a problem when used as the core in kernmantel rope construction. While not specifically applied to sailing, it still weighs the plusses and minuses of each fiber. How you choose is relative to the application. When looking at how a rope fails, remember that friction results in far more rope failures than breakage due to elongation, thus buying a rope with better abrasion resistance may ultimately yield the stronger rope in a yachting application. Also, remember that in a double braided rope, friction occurs within the rope, not solely on the cover. Cost can be a deciding factor too. For recreational sailors, buying a blended core rope will give sufficient performance without breaking the bank. Chuck Gilchrest S/V Half Magic 1983 35 Landfall Padanaram, MA From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Gary Russell via CnC-List Sent: Monday, November 14, 2016 7:24 AM To: C&C List <cnc-list@cnc-list.com> Cc: Gary Russell <captnga...@gmail.com> Subject: Re: Stus-List Switching to rope halyards My rigger recommended Technora over Dyneema. I think they said it was a durability issue, but not sure. So far, I'm happy with the Technora over wire. They bulked up the genoa halyard in the clutch area. That seemed to work well, also. Remember to take those lines down for the winter and replace with tag lines. I must say, they don't give that stuff away! Gary S/V Kaylarah '90 C&C 37+ East Greenwich, RI, USA ~~~~~~~_/)~~~~~~
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