Author Topic: Load release on a bight?  (Read 3515 times)

Thoreon

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Load release on a bight?
« on: March 31, 2015, 04:58:35 PM »
Hi All,

new to this forum and despite being the "knot-guy" in my rock climbing group I apparently seriously underestimated the amount of things one can know about knots... *nod of the head*

Anyway, I've been playing around with rope swings. Hang someone (in a harness!) from a high branch, pull them sideways and upwards and let go; easy. But if you scales things up you quickly need hauling systems. Just letting go then causes the rope to fly trough pulleys at alarming speeds and whipping people in the face etc...

So if you have a look at the representation in attachment. I want a knot that releases person 3 when person 2 pulls on the B end of the red rope. I know there are many load releasing options for this; and that I could just let person 3 do the letting go himself with the possible aid of a belay device; but I want the red rope to cleanly and completely let go of the carabiner that attaches it to person 3. I want to avoid it running through the carabiner causing drag and rope burn. I have yet to find and option that does not run through the carabiner and is strong enough to take the forces involved... Any ideas?

I came up with (or it might already exist but i didn't find it) a working option; basicly a double stranded super munter where the (now bight) tail end is held in place by a tumble hitch using one of the standing ends that now functions as a release.(pic in attach). It works; and releases cleanly, but it's a cumbersome and delicate knot to tie...there has to be a better option...?

cheers!


http://www.animatedknots.com/muntersuper/index.php?Categ=typeslidegrip&LogoImage=LogoGrog.jpg&Website=www.animatedknots.com

roo

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Re: Load release on a bight?
« Reply #1 on: March 31, 2015, 07:34:52 PM »
I want to avoid it running through the carabiner causing drag ...

Maybe just outside of the carabiner you could place a Trigger Bend:

http://notableknotindex.webs.com/triggerbend.html

If you let the suspended person pull it themselves, it'd reduce rope length substantially.  There will still be some initial drag, but short of using a special device, there may not be a way around it.
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SS369

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Re: Load release on a bight?
« Reply #2 on: March 31, 2015, 11:05:34 PM »
Hello Threon and welcome.

If man A is doing the work and the other ground man is the trigger man, then I could suggest a highwayman's hitch. http://www.surreyknots.org.uk/50-highwayman's-hitch.htm

Or you could use a stone knot with a fiddlesticks. http://www.canyoneeringusa.com/techtips/fiddlestick/

Basically a tethered toggle. It wouldn't necessarily have to be tethered, as the harnessed swinger could pull the pin at his choice of time.

SS

Thoreon

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Re: Load release on a bight?
« Reply #3 on: April 01, 2015, 12:58:04 AM »
Cool, thx for the ideas guys. I've tried the highway man's hitch before, but it doesn't hold well enough to hold body weight at large angles between the ropes when you are easily putting 200+kg on it. Maybe with a different carabiner shape/rope diameter. Some kind of stone knot + fiddlestick like object probably works but I'd like to keep it "gear that is usually in my climbing backpack anyway".

Ill try the trigger bend and see how it holds up under larger loads. I'll experiment a bit with different rope diameters etc and let you know. It does mean using a second short rope to connect the harness to the hauling rope via the trigger bend (so that the hauling rope can also provide the triggering end)... Not a problem as such, I just can't believe there is no good knot that does it with 1 rope while the trigger man is on the ground!  (Not that I've ever hauled someone up a tree that was then to afraid to trigger; while we were unable to unlock our hauling mechanism while loaded... or anything... ever... definitely not ::)

Thoreon

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Re: Load release on a bight?
« Reply #4 on: April 02, 2015, 01:47:54 AM »
So I tried tumble and highwayman hitches, unfortunately they fail with heavy and moving (read: screaming?;) ) loads. Again, maybe it's me not tying them properly or the limitations of having to tie them on a carabiner.... Stone knot with a triggering object works well enough but I'd like to avoid it. Trigger bend also works well with the thinner rope wrapped around a thicker rope. they are kind of prussik like after all. But it's a pain in the behind to tie when you want a long trigger end like I do.

So after some reading on the forum, it turns out that the name of what I am looking for is an "exploding hitch" at least according to Knot4U.
 
Quote
I put the Highwayman and the Tumble in a special category of "exploding" hitches. They are beyond merely quick release. As you know, an exploding hitch is a hitch that causes the rope to be completely removed from the object when the slip is pulled out.
 ? Re: Siberian Hitch Reply #10 on: July 03, 2012, 09:32:07 PM ?

Quote
I would never use an exploding hitch for a critical application. So, I'm not obsessed with finding an exploding hitch that's highly stable. Unfortunately, the more stable exploding hitches (e.g., Tumble and Tumble Timber) are also more complex. I figure an exploding hitch is something to tie super quickly and untie super quickly.
? Re: Siberian Hitch
? Reply #12 on: July 03, 2012, 09:32:07 PM ?

Contrary to Knot4U though, I AM looking for a knot to use with "critical" loads (not really, since a failure will lead to a premature swing rather then a fall; but still, I want to trust them.)
So does anyone know of any "exploding hitches" (by Knot4U's definition) that are stable? Or does anyone have an ideas on how to improve on my super munter on a bight + double slip knot tie off combination? The problem is mostly that you have to keep it constantly tight while tying it or it will slip a lot.

As an easier representation of what I am looking for: a knot that can tie a piano to the ceiling, and if I pull the tail end of the rope from the ground the piano unties from the rope, falls, and leaves me with a rope in my hands that is still attached to the ceiling... I assure you I have no evil intentions or cartoon re-enactment fetishes.;)

cheers
T

roo

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Re: Load release on a bight?
« Reply #5 on: April 02, 2015, 02:10:25 AM »
Trigger bend also works well with the thinner rope wrapped around a thicker rope. they are kind of prussik like after all. But it's a pain in the behind to tie when you want a long trigger end like I do.
While it can be tied in the bight if you organize the steps of tying (form the on-the-bight coils first), I'm unclear as to why the suspended person cannot pull the trigger themselves. 

You might look over andy753421's  instructions.png here:
http://igkt.net/sm/index.php?topic=1621.msg11100#msg11100



It probably doesn't need a lot of layering.  It's too bad he's not around to ask him what it should be called. 
« Last Edit: April 03, 2015, 07:53:19 PM by roo »
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Thoreon

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Re: Load release on a bight?
« Reply #6 on: April 02, 2015, 03:18:23 PM »
Eureka guys! It works!

So tried the tumble hitch; highwayman hitch and andy753421's hitch. I attached a 9mm static rope to a tree with these 3 knots and I tensioned to another tree with a 5:1 mechanical advantage, pulling with 2 adults. Then we both sat on it to further tighten the knots. No dynamo meters available, but we would have went well over 400kg/882lbs. They all held this time, but the tumble and highwayman both settles into twisted and awkward positions, the andy753421 did fine. However, as was to be expected, in every case the release slip got VERY tight and it took some VERY decisive full body weight janking to get a release.

The solution was to incorporate a munter hitch into andy753421. Instead of just the loop in step 0, wrap the loop around the standing end and back through the carabiner before proceeding to step 1.



The munter reduced to load on the slip by considerable factor (just like the munter-mule) and made release easy! Unlike the andy753421 the tumble hitch and  highway man use two loops to go around the objects, making a munter combination with them troublesome.

@roo
Quote
I'm unclear as to why the suspended person cannot pull the trigger themselves. 
Admittedly it's a bit of a gimmick to have the release from the ground option in this set-up, it ads a bit of fun and drama, but that's it... Of course now you can also use it to drop a dead weight cleanly...  if you are a myth buster or something, can't think of any other realistic situations:p

xarax

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Re: Load release on a bight?
« Reply #7 on: April 02, 2015, 04:41:12 PM »
This is not a knot.

Dan_Lehman

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Re: Load release on a bight?
« Reply #8 on: April 03, 2015, 05:31:52 PM »
. I've tried the highway man's hitch before, but ...

I'm  quite dismayed that any "knot tyer" would recommend
the treacherous highwayman's hitch --that knot's problems
were revealed over a decade ago and given some promulgation.
Expressly on account of that, I developed (and saw published)
a simple variant that takes the full force of the S.Part off of the
"toggle bight" and so both avoids the risk of capsizing from
that force and offers some easier freeing of the knot under load.
Cf. http://notableknotindex.webs.com/tumblehitch.html
and note the rationale:
Quote
This hitch's stability makes it far superior to the related Highwayman's Hitch,
[which] rightly draws the scorn of knot tyers, tending to capsize to the point
where the draw loop no longer functions, or coming undone under strain
or motion, depending on conditions.

Now, I see that you have come to this (and the offending) hitch,
and found it wanting.  I'm not terribly surprised, depending upon
the relative diameter of the tree to which you hitched --the greater,
the more problematic.  But I wonder also how well you set the hitch,
for with the slip-bight/toggle part drawn firmly, there shouldn't be
much room for the twisting "into awkward positions" !?  (I should
remark that Grog & I had an exchange about the stability and
effect of this "slip-free" hitch and he remained unhappy with its
behavior in some cases, and maybe he doesn't present it --I forget
where we left off.)

Quote
So tried the tumble hitch, highwayman hitch, and andy753421's hitch.
I attached a 9mm static rope to a tree with these 3 knots and I tensioned
... well over 400kg/882lbs.  They all held this time, but the tumble and
highwayman both settles into twisted and awkward positions, ...

But you are anyway right about the force against spilling the knots
when desired --a common mistaken belief : that putting in a slip-tuck
renders the knot easily untied(!)--, and are on the right approach
to redress this by building a structure that first reduces force/tension
in the rope, and then working in the release.  (This is like the
parachute-release mechanism in which a stout ring is pulled back
and held by a smaller ring, which itself is similarly held by a ring
smaller and with then only mild force involved --and releasing this
smallest ring is thus easy, and from it go the others.)


--dl*
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