Knotting rope at 1mtr before pitch length to prevent sheath slippage.

[ronaldjprice]

I am not talking about end knotting rope to prevent abbing off it.

On a recent trip someone insisted on knotting the rope about 1m up from bottom of pitch, to prevent hitting the deck if sheath should fail.


Never done it before or since, just curious as to the need, with modern SRT rope.

Thanks
Ron

 

[langcliffe]

On a recent trip someone insisted on knotting the rope about 1m up from bottom of pitch, to prevent hitting the deck if sheath should fail.

Never done it before or since, just curious as to the need, with modern SRT rope.

Steph Gough had the sheath "fail" on some Bluewater when reconnoitring the big pitch in Rathole, but that was because it got sliced by a flake. When he tried to prussik past the damaged section, the sheath slipped about a metre, so he abseiled back down to the ledge. I gather that there was no slippage on the descent.

I remember Dave Checkley telling me that some Russian ropes have very loose sheaths, so you can finish up at the bottom with a vast amount of sheath wrapped up in the descender.

I would say that with the ropes commonly in use in the UK, using reasonable rigging to avoid the sheath being damaged, there is little chance of failure, and that judging from Steph's experience you wouldn't get very far if it did.

 

[Les W]

Knotting a rope 1m above the ground on any pitch of consequence will not prevent hitting the deck anyway.
If we assume 6% stretch of a semi-static rope then that equates to 6cm per metre of rope. If the pitch is greater than about 17m (16.666) then the amount of stretch available will be greater than 1m, so you will hit the bottom in a shock load situation such as free fall onto the knot. This will obviously depend on lots of variables (actual amount of stretch in a rope, weight of person falling, distance of falling, amount of rope available, velocity, etc.) but I'm pretty sure a knot 1m up will not prevent somebody hitting the ground on anything but a short pitch.

I have seen people tying a slip knot as high as they can reach (2.4m ish) to protect novices from out of control descents when learning to abseil, but never to prevent sheath slippage.

 

[langcliffe]

Knotting a rope 1m above the ground on any pitch of consequence will not prevent hitting the deck anyway.

I suspect that the thinking is that the sheath will slip gradually and accumulate at the knot, so shock loading wouldn't come into it. On the other hand, if that were the case, one might as well gracefully slide to the bottom anyway!

 

[ronaldjprice]

Glad to hear that.
Thanks guys,

 

[Burt]

I've had a little experience of this. Whilst abseiling a group one of them decided to pendulum and almost instantly the sheath broke on the static rope. Turns out it rubbed over a particularly sharp edge- and made a hell of a tearing noise. Anyway, the inner held and the client was lowered on the safety rope. Concerning, but nobody hurt. The sheath on the ab rope concertinered up and bunched under the fig 8 but due to the safety rope catching the fall, it didn't go very far. I suspect that it would not go much further than about a meter as it bunches up lots.

In this case the sheath had been damaged by an edge. I have never heard of a rope sheath breaking due to simply abseiling on it - unless it had previous damage. In which case why didn't you check your rope when you put it away last time?

Knotting the rope may slow down a sliding abseilier but as Les says the stretch in the rope will bounce the victim into the ground. If the sheath broke 2-3 m above ground then the victim would be protected by the knot, but not if he was say 10m up. However, if he was just above the 2m knot then the sheath broke, it would be bloody hard to get him off the rope cos the knot's in the way!

I can think of plenty of reasons to knot the rope at the end to prevent abbing off it but not many for knotting it 2-3m above pitch bottom.

 

[Cave_Troll]

i had a sheath breakage incident down the berger. i only slipped  < 0.5m while going up.

 

[shotlighter]

i had a sheath breakage incident down the berger. i only slipped  < 0.5m while going up.

I've heard of stranger places to do it, but must admit I didn't realise you're so well endowed - how's the poor lass, are you a father as a result!
Sorry but couldn't resist!