Author Topic: When a slip is knot  (Read 2697 times)

KC

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When a slip is knot
« on: February 19, 2016, 01:49:25 AM »
Over the c(o)urse of decades of getting by with whatever immediately in reach thru hot, heavy, nasty; and a lot of mistakes;
i have re-learned much of the already obvious, and perhaps then some.
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i've found that even a slipped half-hitch (HH) doesn't always slip free.
If you snatch and stretch nylon a lot, it can fuse/melt.
1 working way to do this is pulling with machinery/vehicle as a mule to pull logs, pipe, muscle trees over (to steer and also force stronger/ more  supporting hinge in response) etc.
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Another complication to same is a round ball hitch; especially with stronger sloped base.
You can jam a slipped HH real tight with pull if sloped side of ball etc. pinches together the loaded, shrinking(stretched) line right,
then stop pulling, line can be wedged in there pretty good(bad); especially when tension comes off and stretched line seems to expand some in that wedgie, add a little heat fusion and it won't slip out like book says!
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You should really pull from point in line with frame anyway(rather than ball) to not leverage bumper, as force goes to frame(unless angled supports run off frame to hitch) anyway you work it.  It is best to have some turn(s) to take brunt of loading, then slipped HH or if on ball_hitch, Bowline eye.  It is okay to load to turns on rounded tow hook inline with frame, and then Bowline on ball because that is inline and buffered force line at that point.  Even trusty Bowline hard to untie if just throw over ball or  hook and snatch hard and drag, really work hard.
« Last Edit: February 19, 2016, 02:17:20 AM by KC »
"Nature, to be commanded, must be obeyed" -Sir Francis Bacon
We now return you to the safety of normal thinking peoples.
~ Please excuse the interruption; thanx -the mgmt.~

Dan_Lehman

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Re: When a slip is knot
« Reply #1 on: February 19, 2016, 07:09:23 AM »
i've found that even a slipped half-hitch (HH) doesn't always slip free.
If you snatch and stretch nylon a lot, it can fuse/melt.
I've long argued against the naive belief often expressed
(& published) that somehow slipping a knot --often said
about the constrictor-- ensures easy untying.  In fact,
pulling out the last bit of slip-bight can run into the
trouble of a bulge of material and the resistance to
bending in the material --as well as needing to overcome
all the friction that makes untying the unslipped knot
difficult.

Quote
You should really pull from point in line with frame anyway(rather than ball)
I distinctly recall someone's reporting an incident in which
some off-road rally/fun-making (men ruining the environment
sort of "fun") vehicles tried to free one vehicle that was
stuck/hung-up : some stout webbing (IIRC) was attached
to the >>ball<< and winched or pulled and ... BAM,
the ball broke off and got embedded in the pulling vehicle's
engine !!  That's an eye OPENER!   :o
(And this might've been some chatter from an arborists' site.)   :)

--dl*
====

DerekSmith

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Re: When a slip is knot
« Reply #2 on: February 21, 2016, 08:25:48 PM »
A few days ago, I took down a large Ash bough which extended out horizontally over the neighbours garden.

The whole bough was over 30ft long and I estimated it to be ca 500lb.

Where it joined the trunk it was about 8" diameter, so I supported this end with a 2,400lb BS rope.  But I needed to ensure the bough would swing back across the fence and not crash down into the neighbours garden.  Thinking that the bulk of the weight was going to be taken by the 2,400lb rope, I used a 1,200lb rope tied as far out along the bough as I could safely get it, to support the branches as they swung back.  This lighter rope was taken over a high branch and then taken down and fastened around a stought old Elderberry trunk.  I used a Truckers hitch so as to be able to pretension the rope and ensure the bough would start to swing away from the neighbours garden as soon as the cut was made.

All set up, the face cut was made to 'fell' the bough in the direction of the rope pull.  The back cut was made and the bough made a copybook 'fall' away from the neighbours garden and fence.  As the bough came back over the fence, the hinge finally broke and the mass of the bough settled onto the 2,400lb rope.

The intention then was to release the truckers hitch and lower the branches, then lower the bough using a friction plate.

BUT, I had misjudged the placing of the lighter rope.  There was actually very little load on the heavy rope and the lighter rope was tight as a drum.

I had tied off the Truckers hitch with a slipped half hitch, and without thinking I heaved on the end to pull the slip out from under the HH.  Yes, you guessed it, as soon as the loop closed at the HH, it refused to go any further...  an there I was - knot jammed solid and 500lb of timber swinging gently in the breeze on a rope that was way overloaded.

I finished up bracing the the branches with a ladder to take a large proportion of the weight off the rope, then I had to use a spike to lever the hitch open in the unloaded rope, then remove the ladder prop and lowered the branches to the ground.

Two lessons learned -
1.  Don't misjudge the weight of twiggy branches, and
2.  use a couple of turns around the anchor before using a slipped hitch so as to keep load off the slipped HH.

Derek

KC

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Re: When a slip is knot
« Reply #3 on: February 24, 2016, 11:06:21 AM »
Wish i was there to help.
Tough calling balance points and line tensions, it does take lots of experience.
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i'm not favoring any slip for overhead load, especially moving.
i think RT +2 HH is pretty simple and clean; easily upgradable to Dbl.RT.
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i'm kinda a Running DBY rigger myself, sometimes with preceding HH on spar for quickie.
More pro would be modular: eye in line to krab and sling on load.
Generally steel krab in eye of line for carrying thru tree all day and as throw weight.
Also cheat by leading HH('s) on load to 'running krab'; this is 'illegal' as you are leveraging a flat krab across round surface;
BUT; with leading HH('s) taking hit; risk effectively neutralized IMO.
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On slips always have to evaluate if load might bump something and strain come off lacing and if pull end of slip gets snagged;
either could have disastrous results in overhead loading.
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Hinging wise: In most conditions would look to use single line at good point that pulls load over/around;
and think of hinge as a 2nd rope that is a butt tie, that assists moving load into position, and handing off to rig line;
then cut hinge free like untying a slip once load right on rig line.
"Nature, to be commanded, must be obeyed" -Sir Francis Bacon
We now return you to the safety of normal thinking peoples.
~ Please excuse the interruption; thanx -the mgmt.~