UKC Forums - Prussic knot on twin / double ropes

Prussic knot on twin / double ropes

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AndyWatt83 25 Apr 2010

Hopefully a quick 'n' easy question for you old trad-heads out there:

Protecting an abseil down a twin rope, should you:

A: Use two prussic knots, one per rope
B: Use one prussic around both ropes
c: Other

Cheers

DWilliamson 25 Apr 2010

In reply to TonyThePrawn:

I've always used B without problems, and I can't find any dissenting viewpoints in a quick Google search. A separate prussik on each rope sounds overly fiddly and difficult for efficient abbing to me.

Andy Nisbet 25 Apr 2010

In reply to TonyThePrawn:

B: Use one prussic around both ropes

Separate prussicks wouldn't work (for sure), as each one could press against the other and stop them locking

Mark Stevenson 25 Apr 2010

In reply to TonyThePrawn: B.

Ideally you should use 5mm cord with thin c.8mm ropes. 6mm will still work ok but the 7mm cord I've seen some people have for prussik loops is too thick to be really confident it will always lock-up on thin ropes.

Alex Buisse 25 Apr 2010

In reply to TonyThePrawn:

As others have said, B. The ratio of prusik diameter to rope diameter should be as high as possible to offer the most friction.

David Coley 25 Apr 2010

In reply to Alex Buisse:

> (In reply to TonyThePrawn)
>
> As others have said, B. The ratio of prusik diameter to rope diameter should be as high as possible to offer the most friction.

Are you sure about that? That would mean one would use 16mm pussic with 8mm rope (16/8=2), maybe you meant as low as possible, eg, 4/8=0.5)

Alex Buisse 25 Apr 2010

In reply to David Coley:

Right, my bad. I still think most reasonable people understood what I meant, though.

gg4419 25 Apr 2010

Klemheist using a small sling? Found this was a good solution for a similar scenario when escaping the system when the anchors were out of reach.

franksnb 25 Apr 2010

In reply to TonyThePrawn: B, with thinner cord than climbing rope ie 7mm prussic cord is not good for 8mm climbing rope

Anonymous 25 Apr 2010

In reply to TonyThePrawn:

> ... question for you old trad-heads out there:
>

Most 'old trad-heads' wouldn't use an abseil prusik at all.

bpmclimb 25 Apr 2010

In reply to gg4419:

Klemheist can't be released when loaded, unlike the French prussik - which is why the latter is the usual choice for protecting an abseil.