UKC

Can anyone provide answers to the following please:

1) What is it about a rope, other than that it is designed to be used as a half/single, that makes it a half/single rope? It's not simply the diameter, as some single ropes are thinner than some halves.

2) I always assumed that, partly due to their thinness, half ropes typically have more stretch than singles. So a half will put less force on the gear in a fall than a single, but you will fall further. Is this correct?

In reply to Michael Gordon:
I'm not sure that your assumptions are correct.

As far as I was aware, half ropes are simply thinner and therefore lighter. You are using two so you want them to be lighter. Also, they are trad ropes so are likely to take less punishment that a single rope which is likely to get fallen on day in day out. So being thinner probably means they'd be outlasted by a single rope if used in the same way.

But one half rope is plenty enough to take a full fall. In theory you're spreading the load a little across the ropes, but I would think in reality, whichever rope you last clipped into gear is going to take nearly all of the load in a fall.

I've done plenty of winter climbing on just one half rope, and have taken one big fall in trad where only one of the half ropes came into play, and coped admirably.

As for more stretch, I don't imagine that to be the case. I could be wrong but I can't see why that would be the case.

In reply to Michael Gordon:

You can have a long lasting hard wearing rope, a light rope, a cheap rope, or a rope that won't absorb water, but you can't have them all in one rope.

The thin singles and triple rated ropes have a lower sheath to core ratio than a half rope of the same diameter, since the core is the part of the rope that provides the majority of the strength. The trade off is that you get less sheath which is what protects the core, less sheath means with like for like use it wouldn't be expected to last as long.

In reply to Michael Gordon:

I presume you've read this thread?
http://www.ukclimbing.com/forums/t.php?n=599567

Single/half/twin are UIAA definitions.

In reply to Michael Gordon:

No sooner had I posted my reply than this appeared on my Facebook wall:

http://www.highinfatuation.com/blog/straight-from-the-mammoths-mouth-things...


Lots of good info there.

In reply to neilwiltshire:

Good clear article, thanks for that!

I get the impression that the key thing in rope construction for singles/halves is what the ropes are typically used for (sport vs trad/winter/alpine) rather than whether they are designed to be used on their own or not. Of course, the advantages of using two ropes for trad are more than just as a back-up for one getting badly cut/abraded (e.g. reduction of rope drag).

As for the question of stretch, I'd have thought that for 2 ropes of similar specification but different diameter, the thinner one will stretch further under the same force (under the assumption it takes more force to stretch something thick than something thin)?

In reply to EddInaBox:

Thanks

In reply to Jamie Wakeham:

I did, thanks

In reply to Michael Gordon:


That depends on the construction of the rope. Nylon is not, on its own, particularly stretchy - the stretch comes from how the fibres are laid down (with a certain 'springiness' built in). I suspect most of the stretch comes from the core rather than the sheath? As such, the sheath/core fraction probably affects the springiness. It is also not true that rope density (grams/metre) is the same for ropes of the same diameter - some ropes seem to just be 'fluffier' (lower density) than others, and this may affect the springiness? (just guessing).

In reply to andrewmcleod:


I also thought that might be the case. But we're both speculating!

In reply to Michael Gordon:

Obviously ropes are all made of fibres or filaments, the filaments are twisted together to make thin yarns or threads. For the core a number of these threads are twisted again (in the opposite direction to the twist of the filaments in the thread) to form thicker strands, there are perhaps seven or so or these strands in the core (about half of the strands are twisted clockwise and half anti-clockwise to balance each other out) it is the tightness of the twist in these strands that determines how stretchy the rope is.

In reply to EddInaBox:

The tighter the twist, the less stretch?

I wondered what the difference was between dynamic and static ropes, concluding the fibres were perhaps different material. But that's maybe not the case?

In reply to Michael Gordon:

It is slightly more complicated than that, the more twists the greater the stretch (think of two springs, each the same length and same diameter, if the first spring has five twists and the second has 10 twists then a longer wire is needed to make the second spring and it will stretch more) but to get more twists you twist tighter, which makes the rope stiffer so handling and the ability to knot it suffers.

Static ropes either have a braided core or parallel rather than twisted strands in the core.

In reply to EddInaBox:

That's interesting! Cheers