UKC

Hi, just taken intro course in lead climbing and have bought my first dynamic rope. On the spec it says it will stretch not more than 25% on first fall. It’s a 40m rope, does that seriously mean it will stretch up to 10m on first fall?? Should I climb above 10m and jump so it’s prestretched & a subsequent fall from say 7m wont result in me hitting the deck?

It will only stretch to its maximum in a severe fall ie factor 2. The stretch will be much less with lower fall factors when runners have been placed.  No prestretching needed or desired as this would reduce the strength of the rope, at least for a time 

The stretch in the rope is to absorb energy from the fall in the rope rather than in your body where it would do bad things to you.

Thanks oldie, so it would be safe to fall from 5m on a new rope?

No.  Say the last anchor you clipped was at 10m and you fell off.  There's maybe 12m of rope between the belayer and the anchor and another 2 or 3 metres between the anchor and the climber.  When the rope goes tight there's a lot of friction between the anchor and the rope so it won't just freely flow from one side of the anchor to the other.   Some of the force of the fall is taken by the anchor rather than the belayer.  So you'll get more force and more stretch in the rope between the climber and the anchor than the rope between the anchor and the belayer.   

Bottom line is nothing like 40m of rope is stretching.  

Yes, if you fell with no runners (ie factor 2) from 5m above your belayer the length of fall would be 5m  from above + 5m below your belayer +1.25 m if the rope stretched 25% ie 11.25m (if my maths is correct!). Leaving you about 6.25m below the belayer.

However it is always far better to start placing runners as soon as possible since this reduces the fall factor and thus the impact force on both you and your belayer and it is easier for them to arrest your fall,  I'm sure you will know this from your course.

The force will actually be further reduced, for example by some rope run through many belay devices, and you will be cushioned by your harness,

After a severe fall the part of the rope involved will take some time to regain full elasticity (although they are certified to hold several such falls).

Only if it's clipped into something

Don't worry about the stretch, new ropes are safe to use straight out of the bag. It will be a lot slippier than ropes you may be familiar with though so bear that in mind.

jk

Shouldn't be much of a problem when leading, as there's normally a lot less rope between you and your belayer. But be aware that if you decide to top-rope a 20 m route and fall from the first 5 m or so you will hit the ground.

Which rope is it, 25% sounds an awful lot

Looked up Mammut ropes - 31% stretch on first fall!

Sounds mad I've never noticed much more than normal stretch with a new rope. Interested to hear industry explanation

A quick Google (ie may be wrong) indicates the UIAA maximum permitted elongation is 40%.

You should try pulling a climbing rope to destruction, it's amazing how far they stretch and  how much energy they store.

Beal go up to 38% 'first fall'. Is 'first fall' industry lingo for 'how far it will stretch before snapping'

No, they are are telling you how stretchy the rope is, and, with 38%, that the rope will be unsuitable for top roping a heavy chap like me on a 30 metre route. On the other hand just what you need on a long run out high on a route above rubbish gear, the impact force will be quite low. (But don't fall low down!)

I get why we have stretchy ropes but I don't get this. What is the relevance of 'first' and what kind of fall is it modelled on

This is quite a handy and simple explanation:

http://www.hamradio.si/~s51kq/photo_album/Climbing_and_Mountaineering/pdf_c...

The manufacturer knows what the characteristics of the rope are when they deliver it to you, new and without any falls. They do not know how the rope is used after the first fall so cannot predict the behaviour, which changes with use.

Testing:- https://www.theuiaa.org/documents/safety-standards/UIAA_101_7_ropes_may_201...   enjoy!

I don't think that says anything about it

This isn't particularly clear but maybe they're emulating a 80kg climber falling from 2.3m above belayer, FF2?

Not exactly intuitive!

I would say don't worry overmuch about stretch - it'll cushion the impact of a fall a bit, which is good. Concern yourself rather with climbing with a competent and attentive belayer