UKC

What's the best way (i've nto needed to do this before)? abb down as normal, prussic below belay, stop, put another prussic above belay, put lower prussik and belay on again below knot, lower weight onto this, take top one off...?

In reply to abarro81: p.s. sorry if this has been asked recently - as i'm sure it must have been - did a quick search but couldnt really see anything.

In reply to abarro81:

The easiest way is to tie the ropes together to allow you to clip into a loop at the changeover point. See http://www.aqvi55.dsl.pipex.com/knots/long_ab_slide.htm for how to do the knot.

The basic sequence is:

abseil down to knot
clip short sling or screwgate into loop
move safety prusik to below knot
move weight to sling/screwgate (may need to have extra prusik to stand in to do this)
remove abseil device from first rope and put on lower rope
Remove sling/screwgate from loop
Continue down

The hardest part is the "reverse" prusiking to move your weight below the join.

boB

In reply to abarro81: Sounds as good a way as any. Why though would you want to ab past a knot? 4 ropes tied together? 120m ab? I can't see any possible application for this except preparing/cleaning a very long route with no decent belays.

If we are just talking about a long decent, I would rather do it in 2 pitches as there is a big chance of getting your ropes stuck if you are using 4 ropes.

In reply to RWH:

Big sea cliffs or if one rope gets partially damaged or anywhere where high up where it all goes tits up and you need to get out fast.

In reply to RWH: would be for sea cliff abbs over 50m when we've got 2 old sport ropes to use as abb ropes and dont wanna buy a super-long static one

In reply to RWH:

Getting to the start of American Beauty on Lundy is the first instance that springs to my mind..

Lots of others .. if you think this is so unusual, perhaps you need to get out a bit more..

CJ.

In reply to abarro81: OK sea cliffs point taken. Sorry am 6 largers the wrong side of sober.

In reply to abarro81: have you got any mates who work in rope access? they could probabley gey you an old 100m static for free. My mate in access got me one.

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In reply to abarro81:

Always remember a French prussik can be cipped into a krab, then a sling threaded through to makem a useful stirrup to take your weight off the rope and move past a knot. Also useful for getting a casualty out of the system.

In reply to Tom Ripley Mountain Guide: not really though a few 'friends of friends' do it so i'll have to find out, good idea.

UKC: starting out? i'm insulted

In reply to abarro81:

You could end up decsending on a rope which has damage to it and need to isolate the damaged area with an overhand or apline butterfly.

Have your prussik (french prussik) above your ab device on a quick draw so its easily in reach.
Abseil to the knot
Load the prussik
Pull up some slack from the bottom rope and clip it into your belay loop with a clove hitch (back-up)
Move your belay plate (or ab device) past the knot and re attach
Put another prussik on lower rope and clip to leg loop
Pull the top prussik down (releases under tension) until weight on belay plate
Undo clove hitch and away you go.

Otherwise use a really big fig of 8 which the joining knot will slide through. I've done this on 9mm ropes before.

Bryn

In reply to abarro81:

Byrn is right - or at least, that's the way I do it.

You can do it without the second loop below, if you get the lenght of the first one just right.

I didn't understand Rob's version - it sounded liek the weight would still be on the rope below the ab device and therefore make it impossible to remove.

There's heaps of places you need to do this - sea cliffs, rescues, Lost Arrow Spire...

J

In reply to bryn:

A neat development of Bryn's method is to use an 8' sling to attach yourself to the upper prussik krab with a locked off italian hitch. This enables you to lower yourself onto your repositioned belay plate smoothly, by unlocking and releasing the italian hitch, which will avoid any potential sudden drop from releasing the top prussik. Once reattached below the knot, retrieve upper prussik, remove clove hitch and continue.

Its worth stating the obvious that you need to be very clear about what you are doing here, and to avoid being only attached via a french prussik at any one time. Therefore, as Bryn suggests, tie into the rope below the knot at the earliest opportunity, and only proceed to untie this knot once you are fully ready to proceed.

Jem

In reply to abarro81:

Firstly, if at all possible arrange the changeover to happen at a ledge system or at least some sort of foothold.

Changeovers on a free hng are hard work ! Two things to rememmber are to leave a tie in loop at the change over point and have a short cows tail on your harness when you set off. Did I mention hard work ?

In reply to abarro81:

PS I have heard of people abseiling using a figure 8 simply abseiling past the knot - which presumably has to be a compact knot,

In reply to GrahamD:

over hand knot on 9mm goes through standard fig of 8's. any bulky knots jam up!

bryn

In reply to abarro81:

Start by tying the ropes together as in ths picture
http://www-sop.inria.fr/agos-sophia/sis/Techniques/Knots/doubfish.gif

Abseiling past the knot: using a fig of 8 but you can swop for any device for descent as you desire. Prussiks can also be subistuted with Jumars, ropemen, tiblocs etc

1. Abseil down to knot


2. Clip long cowstail (a long quick draw with screw krabs) into the loop tied in the tail emerging from the knot (see picture above)


3. Put an extended prussik (use a 8' tape )on the rope a few inches above figure of eight.


4. Stand in the top prussik and attach a second prussik to rope between first prussik and figure of eight


5. Release the load on the top prussik off the rope.


6. Down-prusik to knot


7. Transfer prussiks(the shorter one first then foot prussik) from above to below the knot


8. Put descent device on the rope below your prussiks and lock it off


9. Stand in long footloop to unweight the short prussik and untie it from the rope


10. Sit back down and transfer weight to figure of eight, make sure its threaded correctly


11. Remove extended prussik from rope


12. Unclip long cowstail from the rope loop


13. Unlock figure of eight and continue abseiling



hope this clarifies matters a little

In reply to RWH:


Useful where you have to leave the ab rope in and go more than 60m. Lost Arrow Spire in the US is a good example but I'm sure there are a few seacliffs over here where you might want to leave the ab rope in.

Useful in caving too when you accidentally take the wrong rigging sacks on your trip

jk

In reply to jkarran:

American Beuty on Lundy and Mercury at Carn Gowla are two that spring to mind.

In reply to GrahamD:
Crossing a knot is an essential technique in caving, for example big pits like Harwoods Hole in New Zealand (which I have abbed down) and Golandrinaz in Mexico (which I havent) have free pitches of well over 100M in depth.
If you have ever done this you will know that one of the big problems is spin. All ropes spin, and on a long free drop like Harwoods Hole this can be incredibly disorientating.
I would certainly suggest getting lots of practice at this technique in a gym, ideally with someone twisting you around and around, and with a hose pipe pouring ice cold water down your neck, before subjecting yourself to a big abseil off a sea cliff or pothole.
Advanced self rescue techniques are also handy in case you/your mate screws up and can't get out of the knot....plan it ahead very carefully. If someone is immobile in a harness, (say hit by a rock) the circulation to the legs gets cut off very quickly, its potentially a very dangerous situation.

In reply to abarro81: forgive me if this seems like a noob reply but, wouldnt it be just as easy to tie a loop into the rope (similar to the one used to tie a few people into the same rope)on both ropes one above and one below the joining not, when you get to it use two quickdraws to clip[ both into the harness while you unclip the belay from one rope and clip it into the other?

This may not work, if not please be gentle with me.

In reply to I'd rather be climbing:

N.B. Obviously i meant tie the loops before lowering the rope to abb.

In reply to I'd rather be climbing:

Both the technique that I described and the one from Ian McNeill do this - the loop is part of the knot used to tie the two ropes together. The hard part is "down prusiking" to get your weight past the knot.

boB

In reply to GrahamD:


The impression I've been given is that its (Mingulay) going to be steep enough that that won't be an option! I was advised to buy a really long static to avoid having to change over in free space whilst away from the cliff spinning to and fro in the breeze...........

AJM