Does any rigger out there have any definitive spec's on the creep properties of Amsteel (Dyn. SK60)?
How much creep, how much load, over how much time?
I have read over and over again about how "SK60 creeps, so don't use it for halyards".
What I don't yet understand is if that is applicable to me. For example, you could also say that line XYZ stretches too much for jib sheets, but for a 4KSB, maybe that doesn't apply since the loads are lower than say, an IACC boat, or something.
So, what are the specs and figures on SK60 creep? Then I can decide for myself if I am willing to save a few bucks going with SK60 vs SK75 for a halyard.
As an example, here is a paper I found for SK75 creep properties:
This is definitely a fuzzy topic for me, and a read of the above paper might indicate why. But some very patient engineers, the kind of people who would actually find that paper intelligible, have explained that creep is how polymers accommodate stress. They don't do it the way most materials do — fracturing, for instance — but by "relaxing", almost as if their little molecules just got tired of hanging on, and just slipped a bit. Accordingly, how those molecules are oriented will go a long way to reducing creep, but the nature of the materials is such that it doesn't seem possible to eliminate it.
Load over time appears to be the primary factor, and one source had it that you basically have about 100 hours at typical sailboat design loads before the rope creeps. Higher relative loads, and higher temperatures might shorten this time, but at the very least we can unrecommend Spectra for anybody's roller-jib halyard, or any boat on a passage.
As for details, I don't have a number, in terms of percentage of halyard length, for how much a rope might creep, relative to load and time. But before I stopped using it for halyards, it seems like the rope would stretch out at least a couple of inches when it crept. Annoying. And I understand that creep deformation is damaging to the rope, so it's not like you can relieve the load and start over.