Some folks are so stuck on Amsteel that they probably use it for shoe laces (I've seen soft shackle key rings). Others treated as some new fangled nuisance, like polyester sail cloth, that will soon go away. I've been using soft shackles on my genoa sheets for a little while now and I like them. Are there other applications I should consider?
In use
Genoa Sheet attachments. Why? I recently add an inner track which requires changing sheets occasionally (there are 2 sets now). I didn't trust snap shackles on a flogging sail, couldn't justify the expense of J-locks, didn't fancy getting whacked on the head or having the mast pummeled. I could have used stropes tied from polyester line (I did use these for a time), but the strength is close and there is a slightly greater chance of opening (they never did). The hollow braid and slipperiness of Amsteel permits some unique splicing options.
Genoa sheets. I recently installed some line that was donated to me (testing left overs). Turns out
it was 1/2-inch Warpspeed (21,000 pounds BS, $5.67/foot). Stiff as hell but good
in this application, should last a very long time. Nice hard on the wind, where stretch means the sail gets full when a gust hits, which is when you want it flat. But I would not have spent $300 for it! I didn't realize it wasn't Staset until I saw how it handled and looked more closely at the core.
When something wears out
Lifelines. Certainly, in a few more years. I will go 1/4-inch with 9/16-inch webbing on the wear spots, which even with UV should be good for 10 years. Easy to do, nice hand, and light.
Jib halyard. My jib halyard has one tight spot where it passes through the masthead. I think the smaller size will resolve the pinch. I will have to splice to something larger for the jammer.
Spin head attachment. If it breaks. Not likely. Or if I need it elsewhere (more likely).
Spin tack. The metal shackle snags and scrapes on the forward lifeline. This will be converted to a soft shackle soon, certainly before the lifelines are changed.
Bridle to chain. If I lose the Mantus hook I'm testing, Amsteel as either a loop or a soft shackle will be next. Easier than the plate I was using. Honestly, for me a sling and carabiner work very well.
Main Halyard. Lower stretch would be nice, but that will be some years.
Topping lift. Light, don't often adjust.
Bad applications (to me)
Spin sheet attachments. Snap shackles are faster.
Main halyard. I prefer a knot. Easy to trim a few feet every few years, to move wear spots.
Jib halyard. Only pin shackles fit furler.
General block attachment. I would be open to this, but in any cases there are sharp edges. Pin shackles generally last forever.
Lashings. Generally nylon or polyester are strong enough when passed many times. Amsteel knots poorly, giving no increase in security over a good lashing.
Main sheet. I want some stretch during jibes; a high mod line increases the stress on the traveler bearings. I wish my traveler was not Spectra and I will change it if I find something cheap.
Jib sheets. Good application, but not cost effective for this boat. I have polyester for my reaching sheets, which is fine, and Warpspeed for the windward sheets which is perfect for that.
Spin sheets. Again, I like some give.
Tying things on deck. Poor knotting, simply don't need the strength.
Anchor bridle. You need the stretch of nylon with chain. But if you are using all-nylon rode, Dyneema may be just the thing to limit yawing; I've tested it, it works.
Jacklines. It depends. On smaller boats the stretch of polyester reduces forces. On larger boats, Dyneema is perfect.
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And so it seems to be limited in application. Neat stuff, though.