"Many experts recommend that cruisers carry extra shrouds and stays. To save space, I’m thinking about carrying Spectra line as a backup. Does the idea have any merit?"
— Kim Barr , San Francisco, California
Win Fowler replies: In theory, Spectra or Dyneema line—both are high-modulus polyethylene—will work fine as standing rigging in terms of breaking strength and stretch resistance. However, you can’t simply toss a coil of the stuff in a locker and think you can pull it out and replace a shroud. You have to anchor the new shroud, and you can’t just tie a bowline around a clevis pin; knots and tight turns can reduce the strength of high-modulus cordage by 60 percent or more. And knots are very likely to slip when they are put under load. This means you must also carry thimbles and splicing equipment and must know how to splice the line so your replacement shroud is strong and properly installed.
Creep, or cold flow, which occurs when the line is under constant load, is another problem. Since the fibers never recover, the result is permanently elongated cordage. Dyneema’s SK78 has the smallest amount of creep, but it’s hard to find and it’s not cheap. In short, while Dyneema certainly can be used as a replacement for conventional wire, using it for standing rigging may cause more problems than it solves.