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Main specification

I need a knot to attach the self blocking non-releasable part of the pulley used to my slackline setup with a small piece of cord. Therefore the knot should be secure for high loads and against accidental releasing. On the other hand it needs to be releasable safely (without fingers getting crushed) while the slackline is still under tension. The release does not have to be controlled however, it is allowed to release fully immediately.

Use Case

I try to find a suitable minimal slackline setup and the method explained here has too much friction for my use case. So I went for a slightly less minimal variant where I use a cord (static 6mm) to setup a pulley. So I needed a one-directional blocking knot/device for this cord instead of the flat webbing. All methods I know from climbing are not releasable under tension (except Grigri which does not block with the 6mm at all and is not really minimal).

Alternative

If you happen to know a knot that blocks in one direction, is releasable under tension and is "minimal" (i.e. using two general purpose climbing carabiners would be fine, using a dedicated device not), that would also solve my problem.

Illustration

As always when I try to explain something, it gets messy and hard to understand. I hope the following schematic drawing can shed some light. Please excuse my poor writing and drawing skills.

enter image description here

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    I'm not sure that I understand what are you doing, but speaking of high loads, releasable and safe, I'm thinking about Munter Mule system or Mule + rappel device. – Usurer Aug 11 '16 at 13:52
  • A munter alone might not be sufficient. A basic rule of anchor-building is to minimize the angles between the arms, otherwise the forces on each arm can be multiplied far beyond the expected load. With slacklines the exact opposite is attempted, and thus the forces involved can be quite large. (I've added a few alternate suggestions to the wiki answer that may be better for larger loads.) – requiem Aug 11 '16 at 15:50
  • I'm a little confused. Is this to tension the slack line or simply to hold the pulley in place? Why does it need to releasable under tension? Couldn't you just release the tension before releasing the knot? – user2766 Aug 11 '16 at 16:46
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    @Liam The pulley is to tension the slackline. The pulley itself has no way to release under tension. So the knot (in place of e.g. just a biner) that attaches the pulley to the anchor needs to be releasable under tension, because there is no other way to "just release the tension". – imsodin Aug 11 '16 at 16:53
  • Waittaminute... a MicroTraxion? Go read this: lorenz-messtechnik.de/english/files/measurements/170243.pdf and then check the safe limits and breaking limits of a MicroTrax. It would be bad if it were to explode on you or shred your rope. – requiem Aug 11 '16 at 17:19
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This is a community wiki to add appropriate knots that will work since there will be several.

  • Munter Mule

  • Tensionless Hitch - Assuming you have a long tail after tensioning your line this "no knot" method may work for you.

  • Radium Release Hitch - This incorporates a munter but also builds in a 3:1 load-lifting system, so unlike a munter it's suitable for "rescue loads".

  • The Mariner's Hitch is releasable under load, but may slip a bit when weighted. This might not be what you want if maintaining tension is desired.

  • The Super Munter tie-off - Builds on the munter to provide increased friction for heavier loads. (Scroll further down the linked page for information.) Alternatively, a mule knot with a Super Munter may work.

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    This is a great idea. However there should be more information like what are the pros and cons of each. Otherwise this becomes a pretty meaningless list of knots. And the Super Munter by itself does not qualify, as it still needs to be blocked somehow (Super Munter Mule), but then a simple munter is ok too (I don't need friction). And rescue loads are not really in scope of the question. – imsodin Aug 11 '16 at 16:07
  • @imsodin I fixed the super munter entry to have the tied-off form. The issues I had in mind (e.g. heavier loads) had more to do with whether a human hand could hold the brake strand and thus might not be an issue for the tie-off knot. Now I'm curious... – requiem Aug 11 '16 at 16:56
  • @requiem In this case a human hand never has to hold the load. When you release the tension it is perfectly sound and safe if you cannot hold the tension, you want to release it anyway. – imsodin Aug 11 '16 at 17:54

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