Vectran forestays

Here, I've looked up a definition for you:

Creep
the dimensional change with time of a material under load. At room temperature it is also called cold flow.

Which is what I said in the passage you first quoted.

Basically, if you pull on a metal spring it will extend a certain % then stop (if at room temperature). If you pull on plastic, it stretches intially (which is what Marlow are quoting you), then apparently stops but actually continues to elongate slowly as time passes. Not significant for short durations, but I guess that over the course of a race your Dyneema standing rigging could creep enough to lose some of its tension. With Vectran that's much-reduced.

Here's what vectranfiber.com say about Vectran:

In experiments on yarns and small braids,minimal creep was observed with loads up to 30% of ratedbreaking load.These tests ran for as long as 10,000 hours at ambient temperatures

I've just read, however, the assertion that provided Dyneema is loaded less than 50% of its rated strength, it won't creep significantly, so maybe the distinction between Vectran and Dyneema is not so important for us. Detailed creep figures tend to be closely guarded trade secrets though, apparently.

All ropes need to be stretched repeatedly, of course, before the fibres align and the rope finds its effective final length (hence your boingy trapeze ropes, I'd suggest, Rick), and it needs to do that every time you coil or uncoil it - maybe a better reason not to use rope in your jib luff. I'd also be concerned about the rope cutting under load - steel wire is much more resistant in that respect.

Nick: why don't you just flake your jib down onto the foredeck? Saves the twisting you get by rolling. I never remove my jib from the boat - leave the halyard and tack attached, flake it and shove the cover over it. Saves all that taping, and I doubt it suffers any more than if it is continually taken off, put in a bag and lugged around/sat on/buckled etc.

I'm using Holt Ultra-line (allegedly Vectran) for my lowers, but have taken to referring to it (when talking to my non-technical - but pretty - crew) as 'the stretchy non-stretch stuff'.

I keep tightening them up, but to be fair, maybe the fibres are still aligning!

I used to do A LOT of competitive archery and there was always  argument about what materials to use for bow strings. Most top archers (then at least) used Dyneema (of one form or another... there are definitely different types). However, it was generally accepted that Vectran had less creep (which was , in isolation, a significant benefit). Then there were string materials which were mixtures of the two... Of course we used to use Kevlar, which had every desirable characteristic for bow strings bar one - it would BREAK, catastrophically and without any warning!

Having said all that, the requirements for bow strings are rather different than those for standing rigging, or artillery linings... I would have thought Vectran was more suitable for rigging due to low creep.

I had vectran rigging on my moth before last. stretched like crazy, and even at 4mm I managed to snap one of the shrouds... Wire is the way, or PBO as Stan says.