# Safety parameters for descent hitches



## Bradley Ford (Jan 20, 2004)

What safety parameters must be met by a hitch used for descent?

Some questions to consider:

What is the maximum weight that the hitch must be able to "control"?

How is "control" defined?

What is the maximum force required to release the hitch while holding the maximum controlled weight?


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## Tom Dunlap (Jan 20, 2004)

My cousin in Wales, Paolo Baveresco has done some research on climbing hitches. When he has the data available, I'll post it. 

There was some research done in Auestralia a while ago. I have the file somewhere in my computer. If I can root it out, I'll post.

Canadian OSHA [?] has done some drop tests too but I only have those in paper form.

Tom


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## Bradley Ford (Jan 22, 2004)

Do you hold your descent hitch (or device) to the same 10:1 safety factor as the other components of your climbing system? If your climbing weight is 200 lbs., do you require your descent hitch to be able to control 2000 lbs.? (For comparison, Petzl reports the normal working load for its I'D descender as 30-150 kg, or 66-331 lbs; 250 kg, or 551 lbs., in exceptional cases.) How much weight must your descent hitch control in order to be "safe"?


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## tjk (Jan 22, 2004)

do'nt forget if you are using a doubled rope system, your hitch only holds half your wieght.


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## tjk (Jan 22, 2004)

The research that I have read shows that a closed ended hitch will slip before it breaks. I have used a distal as an in line anchor on a five to one rig while doing some felling, we had 3 men on the rope and eventually the distal would slide on the host rope.


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## NickfromWI (Jan 22, 2004)

The simple answer is....

It must never break or become untied in use.
It must stop you when you want to be stopped.
It must let you down when you want to go down.
It must hold you if you take a very hard fall on it.

I, like Rocky, like using the 2500lb mark as a guideline, and it's usually very, very easy to obtain. With the great lines that many manufacturers are making, a person could concievably use a line around 3/16ths in diameter and still be beyond the 2500 mark.

This is a good question. One that could use a lot of developing. 

I am assuming that we consider the 2500lb mark acceptable for closed-hitch systems, like if you're using a Distel or VT.

Should open hitches (Tautline, blakes) be held to 5,000lbs? I think so.

love
nick


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## tjk (Jan 22, 2004)

Well said Nick. When I was competing in Montreal I saw some shady things that I think should be point deductions or even DQs. While waiting in the top of the work climb I watched 2 top Euros make thier runs. While they where coming back in after a limb walk thier hitches stayed wide open and self fed. They were using a harder lay cord. They had to "set" thier hitch before wieghting it or they would have begun a very rapid decent.


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## NeTree (Jan 23, 2004)

> _Originally posted by NickfromWI _
> *
> Should open hitches (Tautline, blakes) be held to 5,000lbs? I think so.
> 
> ...



It would make sense.


I only use my hitch for short descents, under 30 feet roughly. Anything more and I set an 8. I can get down faster without burning or putting undue wear on my split-tail.


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## Bradley Ford (Jan 23, 2004)

> _Originally posted by RockyJSquirrel _
> *First, I do not think in terms of 'descent' hitches. My friction hitch is a positioning device suitable for ascent, descent and positioning.
> 
> Second, I do not think in terms of 'how much weight can this hitch hold'. I think in terms of cordage tensile strength and proper tying of a hitch.
> *


I thought knowing how much weight your hitch can control in descent (versus ascent because I thought descent is more challenging than ascent for the hitch) would be just as important as knowing how strong the rope or cord forming your hitch is.



> _Originally posted by tjk _
> *do'nt forget if you are using a doubled rope system, your hitch only holds half your wieght. *


So for the descent control capability of a hitch to meet the 10:1 safety factor in a dynamic rope system with a 200 pound climber, the hitch must control the descent of 1000 pounds ( 200 X 10 / 2 , assuming no friction from the TIP), right?


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## TheTreeSpyder (Jan 23, 2004)

i think we should walk/talk more conservatively; any error in calcs; could multiply on the next error, a string of these errors/assumptions would not put us where we claim to be.

When did rope strength /synthetics requirement drop to 5000?

Is a line wrapped around, rubbing itself (as basket doesn't do) still the same as basket strength?

Samson told me that it wasn't as strong as 2 lines (rope slung over support to hitch load in basket lacing); that they calculate strength in that position at 1.65x tensile not 2x. Saying that the round sling qoted as 2x has more legs, and that is more of a convention to quote 2x, than science.

if we wrap a 5/16" line around anything, wouldn't we still want at least 4x diameter for the host it constricts; which would be over 1"; really to quote at 100%; host should be 8x diameter; and some chords might be a lil'stiff for that general formulae?

So what is the compounding mistake of all these 'errors'?
Everything is being assumed at full strength; yet is prolly comrpomised here and there.

Taking 1/2 of the metal strength; assuming full basket strength even though baskets don't bend over themselves rubbing, assuming a line as a roundsling will be calculated at 2x strength assuming no loss from bend: all could have compounding error; on perhaps the piece taking the most friction?

i'm not saying that they aren't safe, just that a publically proclaimed 2500# isn't conservative/high enough to say that you are staying with the whole rest of the philosophy of SWL; in the smallest, thinnest, newest piece of synthetic gear we may have; that might take the most friction abuse in the smallest area. i think that (at least publically quoted) shold be more towards 3500-4000; why not? Brian's chord recomendation hits that,and is smaller diameter, so could retain more strength wrapping around a 1/2" host.

i believe as Bradley does, that descending on a hitch tests it more than sitting ascending. True sit/ascend has to grip harder and hold so muenter though a descending hitch, and up to those riggers, is not good enuff for the sit/ascend; but i general if it can take the rigors of descending is the true strength and sturdy test to me.

i think that a system is as strong as it's weakest link; if we will cut corners here, why not lower the strength of the whole system?

i think for a lot of non-JP type climbers; the SWL ratio for lifeline gear ends up closer to 20/1. Even though the arguement can be made chord is a temp; i think we should maintain/raise/lower the standards in a planned way across the board.


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## Kneejerk Bombas (Jan 23, 2004)

A good hitch would run when overloaded, then slowly grab, to reduce shock loading in case of a fall.


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## RescueMan (Jan 23, 2004)

TreeSpyder,

The whole reason we use a 10:1 static system safety factor (or 8:1 in Australia, 15:1 in US fire service) is to allow for the weakening of ropes and webbing by knots and tight turns around TIPs. This keeps it simple and conservatively strong.

The alternative is to calculate exactly how much strength is lost in a particular system and size your gear so it can still handle the expected live load.

But instead of wracking your brain with all that engineering, just use the SSSF of 10:1 and you're covered.

- Robert


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## Eagle1 (Jan 24, 2004)

Nick. just curious??

Do you think one can desend soley on a Blake?


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## RescueMan (Jan 24, 2004)

*Descending on a hitch*

Eagle1,

You addressed your question to Nick, but I'll attempt an answer. I assume you mean on SRT (single rope) rather than DdRT (doubled rope).

I've been running this question around myself: is it possible to safely descend on a single rope with a friction hitch. I had previously answered this with a resounding NO, but I'm reconsidering.

The problem with most friction hitches is that they are very compact (this is a good thing, generally), which gives them a grab-or-release operation. This is helpful for ascending a fixed line: once broken they slide relatively easily - once released they grab quickly and reliably.

In order to function as a descender, a hitch would have to offer variable and controllable friction instead of an either/or. I think this is possible with the longer, braided friction hitches such as the VT or the similar hitch used in rope rescue, the Dog-'n-tails (see attached picture).

In the cave rescue community, we've been experimenting with the Dog-'n-tails as a means (actually the ONLY means) of descending a loaded rope (a rope with a casualty hanging on it), as any mechanical rappel device requires slack below the device.

I would be very interested in anyone's experience in descending a fixed single line with a friction hitch.

- Robert


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## Eagle1 (Jan 24, 2004)

Robert. I asked that question because i do believe, and practice decending on a single line, with a hitch (Blake).
I am sure that some would say it is not advisable. I always have a "8" stopper at the end, and I keep my rope in good contition.

I never saw or herd of a blake just "failing" when tied properly. I also would love input on this. 

Rock,---fire away!!


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## John Paul Sanborn (Jan 24, 2004)

*Re: Descending on a hitch*



> _Originally posted by RescueMan _
> *
> In the cave rescue community, we've been experimenting with the Dog-'n-tails as a means (actually the ONLY means) of descending a loaded rope (a rope with a casualty hanging on it), as any mechanical rappel device requires slack below the device.
> 
> ...



I have tried using a VT on single rope, and it was not very fun.

In the scenario you put forward I would want to be belayed on a second rope too (f at all possible)

I think it would be a tool of last resort, vs. SOP. 

How do you think that would work in cave applications set up in a VT form?


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## RescueMan (Jan 24, 2004)

I think the VT, if tied long with lots of braid, is structurally the same as the Dog-'n-tails and would function the same.

I would not descend, however, on the shortened version of the VT I've seen pictured on arborist sites and in these forums.

The attached picture is an incorrectly-labled MT Prusik (actually a VT without the initial round turns - an MT is tied with a closed-loop). And this doesn't have enough braids for me to feel comfortable using as a descent hitch.

We use twelve crosses on the DnT.

- Robert


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## RescueMan (Jan 24, 2004)

*WHOOPS*

Here's the picture:


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## rahtreelimbs (Jan 24, 2004)

> _Originally posted by Eagle1 _
> *Nick. just curious??
> 
> Do you think one can desend soley on a Blake? *



Why not?


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## Eagle1 (Jan 24, 2004)

Wow. An acknowledgement from Rocky. Do you really think that you have to question the fact to another what rope tech. I am refferring to??***-****


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## NeTree (Jan 24, 2004)

So... does anybody besides me actually use a figure-8 at ALL?


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## Bradley Ford (Feb 2, 2004)

> _Originally posted by TheTreeSpyder _
> *i think that a system is as strong as it's weakest link; if we will cut corners here, why not lower the strength of the whole system?*


I believe that when I descend with a dynamic rope system my hitch is the weakest link in my system.



> _Originally posted by RescueMan _
> *In the cave rescue community, we've been experimenting with the Dog-'n-tails as a means (actually the ONLY means) of descending a loaded rope (a rope with a casualty hanging on it), as any mechanical rappel device requires slack below the device.
> *


What criteria does the cave rescue community use to judge the Dog-'n-tails (or any other) hitch?


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## NickfromWI (Feb 2, 2004)

> _Originally posted by Eagle1 _
> *Nick. just curious??
> 
> Do you think one can desend soley on a Blake? *




Well, if you're talking about SRT, I'm tempted to say yes. Now, could a person tie a Blakes out of 1/2" climbing line on SRT and descend safely??? I doubt it, but it may be worth trying. If anything, I bet it'd be a jerky descent.

Now, if you were climbing on an 11mm line, and you tied the blakes out of like a 13mm technora or vectran line, hmmmm maybe you could. 

Someone's gotta try it out, I guess. On belay the whole time, of course.

love
nick


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## Koa Man (Feb 5, 2004)

> _Originally posted by netree _
> *So... does anybody besides me actually use a figure-8 at ALL? *



I do, usually only when I want to make an impressive drop out of a tall coconut palm.


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## Bradley Ford (Feb 5, 2004)

> _Originally posted by RockyJSquirrel _
> *To be honest, I'm not even concerned with how my hitch handles 300 lbs. I have it dialed in for my weight, not JPS's weight. Advanced hitches can be weight sensitive. Therefore you must adjust the number of wraps or braids in order to dial them in for your weight. *


Because your hitch is "dialed in" for your weight, is the hitch the weakest link in your climbing system? (If not, what is?)


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## Eagle1 (Feb 5, 2004)

Using a Blakes, I descend all the time. I use 1/2 rope. It is very smooth believe it or not. You just have to keep your hand under the hitch to control speed. I trust it. I really dont make a habit of it though. Normally if i descend the stick I still have the lanyard, if I have to come down fast, as long as I have a crotch, I have no problem coming down on the Blake.


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## Lumberjack (Feb 5, 2004)

> _Originally posted by netree _
> *So... does anybody besides me actually use a figure-8 at ALL? *



I use it for repeling when I am not on the i'D or i am repeling for fun. I still like the 8, it is smooth and sweet. The i'D is ok (I wouldnt remove it to put on the 8) but for repeling I perfer the 8.


Carl


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## NeTree (Feb 5, 2004)

Glad to see I'm not a COMPLETE dinosaur.


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## Burnham (Feb 6, 2004)

No way, NE, or I'm a dino too. I almost always rappel on an eight. Do you use a deaf 8, one of the small models? Or a large rescue style, w/ ears? How about you, Carl? 

Any of you using a rescue 8, have you seen or used one of the type with ears on the side, versus on the top?


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## NeTree (Feb 6, 2004)

I use a classic "8"... no ears.

Tried the Resue 8 with the ears, but it just leaves something to get snegged on while you're carrying it around, whereas the smooth profile of the classic avoids that.

JMH Preferance...


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## Lumberjack (Feb 6, 2004)

I perfer the Rescue 8, when it is applicable. The ears do get caught up on alot of things, so I put it in the bag on the back of my saddle, if it becomes a problem. I like the deaf 8's small size, but I started using the Rescue when I first started repellin. 

In an emergency (drop the 8 i'D and whatever else) I can and have used the kong bent gates on the side of my saddle (used to hold my junk) to come down on a munter hitch. I have done it before, but just to try it out. Never know when I might need it.


Carl


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## NickfromWI (Feb 6, 2004)

In my streamline state of mine, I don't think the 8 is worth carrying around. When ever I rappel down (as opposed to descending on a friction hitch) I tie a munter. I'll either leave the spliced eye clipped and munter where my friction hitch just was, or I will double the climbing line over my TIP and tie the munter with both hanging ends of the climbing line. 







It might sound bulky, but it works nicely. It's not as smooth as using an 8, and the 8 doesn't put as many twists in the line, but it only takes a few seconds to ket the twists out after rappel and it's one less thing to carry around.

love
nick

ps- I would prefer the 8 if I was doing longer rappels...more material to dissipate the heat.


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## Burnham (Feb 6, 2004)

That's a drawback to the rescue 8, for sure, NE. I would carry mine binered by the large upper hole instead of the regular rigging hole, which seemed to help reduce snagging. Then I got one of Surety's RQ3 Q-8 rescue 8s, which has ears on the side. Actually they are shaped more like horns, or a cleat on a boat deck. Way nicer to use, with easy adjustable friction levels available, and very controllable lock/unlock manuever. But either way you carry it, it can snag. I hang it from a gear sling behind my hip, and for some moves I'll tuck it inside the leg pad on my New Tribe (Ness) saddle. That keeps it out of the way quite well.

You ought to give one of these a try, Carl. It's a big improvement over the usual 8 w/ ears.

I'll try posting a picture.


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## Burnham (Feb 6, 2004)

Here we go...


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## Lumberjack (Feb 6, 2004)

> _Originally posted by NickfromWI _
> *It might sound bulky, but it works nicely. It's not as smooth as using an 8, and the 8 doesn't put as many twists in the line, but it only takes a few seconds to ket the twists out after rappel and it's one less thing to carry around.
> 
> love
> ...




The munter is easy to use, I just perfer having 8's heat sink on all the repels, but the munter is fun. The first time I used it my groundy said "You got a million ways to go up and down the rope"

Also the munter is more involved to lock off than an 8. 

Aint options great?

Carl


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## NeTree (Feb 6, 2004)

As I said, I use an 8 for longer descents, like anything over 30 feet maybe. Otherwise, I just slide down my Blake's.


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## Lumberjack (Feb 6, 2004)

Yea to me the munter is fine to 30-40 foot, if its the easyist to go down on. I wouldn't take off the i'D to use a munter or an 8, unless it is over say 100 foot, then I perfer the 8.


Carl


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## RescueMan (Feb 6, 2004)

> Also the munter is more involved to lock off than an 8



Actually, the munter is relatively simple to lock of with a mule knot.


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## NickfromWI (Feb 6, 2004)

Thank you, RescueMan....never underestimate the power of the slip knot!

I have the book that that image is from.....it's a shorty but a goodie!

love
nick


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## Lumberjack (Feb 6, 2004)

> _Originally posted by RescueMan _
> *Actually, the munter is relatively simple to lock of with a mule knot. *




Yea, the mule can be extremely helpful in some rigging situations. When you get ready to go, just pull the tail and off you go!

Thanks, I had forgotten how to tie it, but remembered the name.


Carl


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## Bradley Ford (Feb 9, 2004)

> _Originally posted by Bradley Ford _
> *I believe that when I descend with a dynamic rope system my hitch is the weakest link in my system.*


Is this a statement of the obvious or just hooey? Assume a safe TIP, new condition arborist rope and work saddle, and perfectly TSD-ed knots.


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## Bradley Ford (Feb 10, 2004)

> _Originally posted by RockyJSquirrel _
> *I do not think of my hitch as the weakest point in my system at all. From what I've been taught, my lifeline would break before my hitch.*


These “ballpark” numbers are my guesses:

My hitch would fail to control descent at a load of 1000 lbs.
My rope would break at a load of half its rated strength (due to knots), or 3500 lbs.
What should these numbers be?


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## RescueMan (Feb 10, 2004)

*Hitch slippage*



> I do not think of my hitch as the weakest point in my system at all. From what I've been taught, my lifeline would break before my hitch.



I don't think the issue was breaking but rather braking, the ability of the hitch to handle the load (friction capacity).



> My hitch would fail to control descent at a load of 1000 lbs. My rope would break at a load of half its rated strength (due to knots), or 3500 lbs.



Most knots weaken a rope by 20-35% - using a 50% stregth reduction factor is very conservative - takes into account normal wear-and-tear of rope as well. 

Don't forget that a fall on a slack rope creates a shock load which can multiply your body weight. This is why a 10:1 or even 15:1 safety factor is typically used for lifeline.

I haven't seen any test results on any friction hitch besides the 3-wrap prusik. But that hitch, properly sized (about 3/4 of the mainline diameter) generally slips at about 1200 lbs force.

The 3-wrap prussik uses smaller diameter cord for better "bite" into the host rope, and a total of 6 turns around the host rope. I would think that a Blake's or tautline, with four turns and made of cord similar in diameter to the mainline, would slip at considerably less than 1200 lbs.

Anyone have any data on the Blake's or tautline?

- Robert


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## Burnham (Feb 10, 2004)

RescueMan, in your field do you accumulate theoretical strength losses to a rope with multiple knots? Or is the knot that has the greatest strength reduction the measure used for the system in question? Or is there some other way of evaluating this question?


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## RescueMan (Feb 10, 2004)

*Strength Loss due to Knots*



> RescueMan, in your field do you accumulate theoretical strength losses to a rope with multiple knots? Or is the knot that has the greatest strength reduction the measure used for the system in question? Or is there some other way of evaluating this question?



Fortunately for those of us who hang our lives on rope, strength loss due to knots (and other tight-radius turns) is NOT additive. Think of the rope as a chain made up of rope segments, each with some kind of knot. The weakest of the links is the only one we need to worry about.

Natural-fiber ropes (which had NO inherent stretch) were weakened in a knot because the fibers on the outside of each turn were taking all the tension, so the weakening was proportional to the tightness of each radius.

With synthetic fibers (at least the plastics like nylon, polyesther, or polypropylene), which have inherent stretch, the weakening is due to the internal friction within the yarns which builds up heat when under load, also correlated with the tightness of the radius and with how many turns are sharing the load (figure-8 better than overhand, eg).

A general rule of thumb to avoid rope weakening is for any loaded turn (around a TIP, carabiner or pulley, eg) to have a radius at least 4 times the diameter of the rope (2" for 1/2" rope, eg).

These are some strength reduction factors due to knots:

BENDS 
double fisherman's bend - 21%	
figure 8 bend - 19%	

LOOPS
figure 8 on a bight - 20%
butterfly - 25%	
bowline - 33%

ROPE WITH A LOOP (pulled end-to-end)	
figure 8 on a bight - 35%	
inline figure 8 - 41%
butterfly - 31%	

KNOTS IN WEBBING
water knot (ring bend) - 36%
overhand on a bight - 35%


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## Bradley Ford (Feb 10, 2004)

> _Originally posted by RescueMan _
> *Don't forget that a fall on a slack rope creates a shock load which can multiply your body weight. This is why a 10:1 or even 15:1 safety factor is typically used for lifeline.
> 
> I haven't seen any test results on any friction hitch besides the 3-wrap prusik. But that hitch, properly sized (about 3/4 of the mainline diameter) generally slips at about 1200 lbs force.*


I think the hitch is weakest when it is used to control descent (versus being used to belay, or hold in place). 1200 lbs. is the 3-wrap Prusik's belay limit, and its controlled descent limit would be significantly less, right?


> _Originally posted by Bradley Ford _
> *Do you hold your descent hitch (or device) to the same 10:1 safety factor as the other components of your climbing system?*


If so, then the minimum capability for your descent hitch is (200 lbs. climber) X (10 safety factor) / (2 support legs of your dynamic climbing system), or 1000 lbs, right? (Note this is about twice as much as the 551 lbs. that Petzl reports its I'D descender can handle under exceptional circumstances.)


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## Burnham (Feb 10, 2004)

So, Bradley, I've been following this thread with interest, and we've covered some good ground, but I find myself wondering again...what is your point?


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## RescueMan (Feb 10, 2004)

> I think the hitch is weakest when it is used to control descent (versus being used to belay, or hold in place). 1200 lbs. is the 3-wrap Prusik's belay limit, and its controlled descent limit would be significantly less, right?



In climbing and in rescue, the prusik is never used as a descent or lowering device. It is a catch-or-release hitch used for ascending or belaying. I know of no friction hitch other than the dog-n-tials (similar to the VT) which is usable as a descent hitch on SRT, though the autoblock as an adjunct on the brake side of a figure-8 descender can be useful to help control speed as well as to lock off.



> If so, then the minimum capability for your descent hitch is (200 lbs. climber) X (10 safety factor) / (2 support legs of your dynamic climbing system), or 1000 lbs, right? (Note this is about twice as much as the 551 lbs. that Petzl reports its I'D descender can handle under exceptional circumstances.)



You're confusing MBS (minimum breaking strength) with SWL (safe working load). The 10:1 safety factor is applied to the MBS of "software" (rope and webbing) to get the SWL. The 551 lbs for an I'D is the SWL. The SWL of a prusik is something less than the 1200 lbs at which is will begin to slip. If tied from 8mm cord on a doubled sling, it would have a MBS of about 6,000 lbs after reducing for the knot and a SWL of 600 lbs.

- Robert


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## Bradley Ford (Feb 11, 2004)

> _Originally posted by Burnham _
> *...what is your point? *


Will any commonly used friction hitch provide safe, controlled descending for 2000 lbs. on a static rope? If so, which? If not, which comes closest?


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## Bradley Ford (Feb 11, 2004)

How much force can Joe Climber be expected to be able to apply to release, for the purpose of descending, the holding friction in his hitch?


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## NickfromWI (Feb 11, 2004)

Perhaps you are planning on using a friction hitch in another application? I am sure you could find a combination of line and hitch cord that would meet your needs, but it would probably take a lot of trial and error.

So why do you need a 2,000lb hitch?

love
nick


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## Bradley Ford (Feb 12, 2004)

> _Originally posted by RockyJSquirrel _
> *What does it matter? In almost 15 years of climbing, I have yet to put anywhere near 2000 lbs of force on my lifeline.*


I choose to climb on a rope with a breaking strength rated well over 7000 lbs.--much more than I'll probably ever need--rather than on less capable ropes. Arguably the most important parameter for choosing a hitch (it has to at least handle the fraction of your weight placed on it by your climbing system) is how much weight it can control in descent. Ideally, my hitch would control the descent of much more than I'll ever need, too. 2000 lbs. was my arbitrary (actually 200 lb. Joe Climber mutilplied by 10), much more than I'll ever need, descending load.



> _Originally posted by NickfromWI _
> *I am sure you could find a combination of line and hitch cord that would meet your needs, but it would probably take a lot of trial and error.*


With enough wraps and braids, I think some form of one of the "advanced friction hitches" would work. Since these types of hitches are so responsive, could Joe Climber break the holding friction in the hitch even under a 2000 lb. load?


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## NickfromWI (Feb 12, 2004)

I think Joe Climber could break the hitch, if the hitch-cord/climbing line combination was right.

If you notice with a smaller hitch with less wraps (say a 5/16ths 3/1 shwabisch) you have to pull kinda hard to break that...to get it to slide. All the friction (while it's holding) is on few wraps. If you use a larger diameter hitch cord and more wraps, the friction is spread over a larger surface area, which ends of needing less of a yank to get you descending.

Maybe if you tied something like a 8 over 8 VT out of 12mm vectran, you might get close to that....but this is all speculation. 

I see where you're getting that 2000lb number. Makes a bit of sense, but probably not accurate for this purpose. I wonder how hard it'd be to descend If I had another person's body-weight hanging from my saddle....

love
nick


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## Bradley Ford (Feb 12, 2004)

> _Originally posted by RescueMan _
> *In the cave rescue community, we've been experimenting with the Dog-'n-tails as a means (actually the ONLY means) of descending a loaded rope (a rope with a casualty hanging on it), as any mechanical rappel device requires slack below the device.
> *


What criteria does the cave rescue community use to judge the Dog-'n-tails (or any other) hitch? Specifically, what load was used on the Dog-'n-tails hitch in these experiments?


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## RescueMan (Feb 12, 2004)

Bradley Ford:


> Arguably the most important parameter for choosing a hitch (it has to at least handle the fraction of your weight placed on it by your climbing system) is how much weight it can control in descent.


Actually, more force is exerted on a hitch in ascent because of the dymanic element of bouncing. It is not hard to place a 500 lb load on a hitch during ascent, depending on how smooth your technique is.



> Ideally, my hitch would control the descent of much more than I'll ever need, too. 2000 lbs. was my arbitrary (actually 200 lb. Joe Climber mutilplied by 10), much more than I'll ever need, descending load


You're still missing the distinction between MBS (minimum breaking strength) for rope and SWL (safe working load) for hitches and ascent/descent devices. MBS is often 10 or 15 times the working load because of all the weakening potential of knots, tight radii, wear & tear, aging, and dynamic loading. SWL only has to be equal to or slightly greater than the load (your weight and the weight of equipment) that you expect to hang on it.



> ...could Joe Climber break the holding friction in the hitch even under a 2000 lb. load?


I haven't seen any test data on arborist hitches, but of all the rock climbing hitches, the prusik can control the most weight (as much as 2300 lbs in some applications), with a 4-wrap Bachman close behind, and the autoblock and kleimheist down at 400-600 lbs. But, because the prusik "bites" so well, it is also the most difficult to release under load (in fact all but impossible - which is why we have to use load-release hitches in series with them in rescue). So I don't believe that any hitch that could control 2000 lbs (lowering a major stem section?) could possibly be released under load. And then, the better the hitch "bites", the less suitable it is for gradual lowering or descent.

NickfromWI:


> Maybe if you tied something like a 8 over 8 VT out of 12mm vectran


You keep touting technora and vectran, two of the new breed of "super synthetic" cordage. I'd be interested in knowing why?

In rescue, these fibers are generally verboten. Independent test results for all the high-strength cords, presented at the 2000 International Technical Rescue Symposium, showed that there is nothing better than good old nylon rope.

While Technora, an aramid like Kevlar but without the self-abrasion problem, is significantly stronger then nylon in tensile strength, Vectran, a liquid-crystal polymer, is actually a bit weaker. And, while nylon weakens only 8% with a figure-8 knot in it, Vecrtran and Technora weaken by 48% and 40% respectively - making them both significantly weaker than nylon once knotted. In a loop tied with a double fisherman's knot, none of the super-cords were as strong as nylon. 

Anecdotally, there have been reports of sudden catastrophic failure of high-strength cords under shock loading, particularly the Kevlar cords which are used today only for fire-fighter's emergency escape lines because of their high melting point and are for single use only.


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## NickfromWI (Feb 12, 2004)

> _Originally posted by RescueMan _
> *You keep touting technora and vectran, two of the new breed of "super synthetic" cordage. I'd be interested in knowing why?
> 
> ...while nylon weakens only 8% with a figure-8 knot in it, Vecrtran and Technora weaken by 48% and 40% respectively - making them both significantly weaker than nylon once knotted. In a loop tied with a double fisherman's knot, none of the super-cords were as strong as nylon. *



RescueMan, I keep bringing up these lines because I want people to think about them and to think about the applications where they can be useful.

Using your numbers...

Yalex (which is polyester, not nylon...but they are comparable) has an ABS of 6,000lbs, at 3/8th" diameter. If you cut down 8% of that (which sounds very generous, if you ask me), you end up with a strength of about 5,520lbs. 

Vectrus, a rope of almost identical construction has an ABS of 16,000lbs at the same size. Subtract the 48%, and you have a strength of about 8,320lbs.

So using your numbers, if breaking strength is your only concern, then high tech fibers still win.

Unfortunately, strength is not the only issue. One of the most important factors that plays in to the high tech lines losing so much strength in a knot is stretch. Nylon, as many know, is quite stretchy. Imagine 2 parallel strands. You lay the two strands parallel and tie them to something. Start pulling on the other end. Chances are, when you tied them, one of the strands ended up a hair shorter than the other. 

When you start pulling, the shortest one will take the load first, then stretch until it is the same length of the longer strand. Now keep pulling and soon both strands will be sharing the load.

This is what happens in rope, but with more strands.

Now same scenario, but with Vectran. You tie, and pull. The shortest one takes the load...you keep pulling. It has such little stretch, it cannot elongate itself until the longer one can help out! Soon, it just breaks, leaving the longer strand to take the load, but it's the same load the just broke the first strand, so it, too, breaks!

This is what leads to the catastrophic failures you mention.

It needs to be remembered that these lines are not just STRONG ROPE. They are different and need to be treated as such. Splices are practically ALWAYS reccomended as the form of attachment, not knots. Proper splicing allows all strands to share the load, maximizing the useful strength of the rope.

Now, if we are talking about a vectran friction hitch...I use it! I have some that are knotted with a double fisherpersons knots and some that have spliced eyes. Either is fine. Even if it lost 75% of the strength, it'd still be stronger than what some people are using for hitch cord.

You raise a good point. That being that in the wrong hands, these high tech lines could be quite dangerous. Be careful what you buy and how you use it.

love
nick


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## RescueMan (Feb 12, 2004)

Nick,

I just looked up the breaking strength of Vectrus, and it IS insanely strong. But that's braided rope and none of the testing I refered to was on arborist-type rope. It was on specific brands of kernmantle rope used in climbing and rescue, so the results are not transposable to the rope you're using.

If you're curious about the testing, go to:

Comparative Testing of High Strength Cord 

Another caution about high-strength cords is that if you fall on them with any slack in the line, it's like falling tied to a steel cable. Because there's no stretch to absorb the force of the fall, a tumble on as little as 4' of slack can create enough force to fracture your spine.

- Robert


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## Lumberjack (Feb 12, 2004)

> _Originally posted by RescueMan _
> *Another caution about high-strength cords is that if you fall on them with any slack in the line, it's like falling tied to a steel cable. Because there's no stretch to absorb the force of the fall, a tumble on as little as 4' of slack can create enough force to fracture your spine.
> 
> - Robert *



I never have 4' of slack in my rope. 

But even if I did, how much does your tress cord really stretch in comparison to the many feet plus feet of rope that it is tied to?

IMO you could tie it with steel rope, and there wouldn't be any appreciatable difference. 

The only diff. in material would be, IMO, their tendencies to slip at a givin weight.

IMHO

Carl


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## NeTree (Feb 12, 2004)

Using a low-stretch line as a tress cord or split-tail would be inconsequential.

Using a low-stretch line as your lifeline could easily break you in half in a fall.

Isn't that why we don't climb on static line?


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## Bradley Ford (Feb 12, 2004)

> _Originally posted by RescueMan _
> *Actually, more force is exerted on a hitch in ascent because of the dymanic element of bouncing. It is not hard to place a 500 lb load on a hitch during ascent, depending on how smooth your technique is.*


I do not think I bounce when I ascend, but maybe I don't understand what bouncing means. Please explain.
I still think it will be more difficult to find a hitch that controls descent of 2000 lbs. than one that will allow ascent for the same load (e.g., as you mentioned, 2000 lbs. could ascend with a prusik, but it could not descend with one).



> _Originally posted by RescueMan _
> *SWL only has to be equal to or slightly greater than the load (your weight and the weight of equipment) that you expect to hang on it.*


I do not think that a hitch that can only support my weight or a little more is safe. If I did "bounce" on such a hitch, wouldn't it fail? And if that was all that was required to be safe, then:


> _Originally posted by Eagle1 _
> *I asked that question because i do believe, and practice decending on a single line, with a hitch (Blake).*


climbers of Eagle1's weight or less could safely use a Blake's hitch for descending a static rope.


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## Bradley Ford (Feb 13, 2004)

*the hitch for descending SRT*

I use "static" and "dynamic" below to indicate whether or not the rope moves through the tie in point (TIP) of the climbing system, not to describe the rope.

If a hitch could control descent on a static rope system of twice the maximum weight capability of either the Tautline (TLH) or Blake's (BH) hitch on the same rope (2 X (min(max TLH, max BH))), then would descending a static rope with this hitch be at least as safe as descending a dynamic rope system with a "frictionless" TIP and the corresponding TLH or BH? (Jepson implied that the answer is absolutely not: OK.....Let's Get Into The Meat Of SRT !!!!)

Ever measured the force required to pull a TLH or BH, complete with stopper knots, to failure on a static line? This force would provide an upper limit to how much the hitch can control in descent. So how much force did it take?

2000 lbs. was an arbitrary weight that I thought might be a safe parameter. I'm guessing the (2 X (min(max TLH, max BH))) weight is less than 2000 lbs, i.e. that the TLH can't control descent of 1000 lbs. on a static rope system.


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## Tom Dunlap (Feb 13, 2004)

All of you arbos need to broaden your views. The rest of the rope world has done a fantastic amount of research into climbing and rigging systems. Even uisng a basic search engine like Google will bring loads of info to your finger tips.

I read a test report about the bounce from ascending. If I remmeber right, Robert will help me here, the climbers were using full on SRT systems. If they would have added a footlock ascent the bounce would have been much higher. Every time you sit on the rope you'll do a mini slam-dunk on the anchor point. It would be pretty simple to setup a test like this. 

Tom


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## Bradley Ford (Feb 13, 2004)

On page 98 of 166 (page numbered 93) from Industrial rope access - Investigation into items of personal protective equipment, a Blake's hitch is reported to have held a 4 kilonewton = 899 pound-force load. This makes me think a Blake's hitch could control the descent of a 2000 lb. load on a dynamic rope system where the load on the hitch is ~1/2 the actual load. This also provides some rational for my earlier, arbitrary use of the 2000 lb. value.

Tom,

I tried googling "ascend bounce test climb SRT", but I didn't see the link to which you referred. Please help.


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## Tom Dunlap (Feb 13, 2004)

be creative with Google. If I were on a payroll I would find theinformation. To me, the search is sometimes more important that the find.

Go to SARBC and root around in the links, it might be there, don't know for sure. 

Tom


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## RescueMan (Feb 13, 2004)

Bradley Ford:


> a Blake's hitch is reported to have held a 4 kilonewton = 899 pound-force load. This makes me think a Blake's hitch could control the descent of a 2000 lb. load on a dynamic rope system


That test was for a static pull to determine ONLY the holding power of a variety of friction hitches. That says NOTHING at all about using a hitch as a decent device.

Some figures on forces from ascending a rope can be found at:Anchor Loads 

There is also a reference to these forces in the test data I posted earlier at the top of page 6 of:
High Strength Cord
- Robert


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## Eagle1 (Feb 13, 2004)

Word up Rock!
I have been reading this 5 page topic for some time now, still have not understood the true question and or why?


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## NeTree (Feb 13, 2004)

Maybe he's expecting a mssaive weight gain?


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## rbtree (Feb 13, 2004)

> _Originally posted by netree _
> *Using a low-stretch line as a tress cord or split-tail would be inconsequential.
> 
> Using a low-stretch line as your lifeline could easily break you in half in a fall.
> ...



Eric, that's where you're wrong. Arbo lines, both climb and bull, are low stretch static lines. Most have 50-70 less stretch than kernmantle static line. 

So, do not fall fall on arbo line, it might hurt. But the limited stretch should save your hide, as opposed to the near zero stretch of synthetic fiber high tech lines like Spectra, kevlar, and Vectran


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## MasterBlaster (Feb 13, 2004)

> _Originally posted by rbtree _
> *
> 
> So, do not fall fall on arbo line, it might hurt. *




The three hard falls I've had suprised me with their lack of violence. Each time, my rope/saddle snapped me upright and I didn't even drop my saw.
This was on safety blue.


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## NeTree (Feb 14, 2004)

> _Originally posted by rbtree _
> *Eric, that's where you're wrong. Arbo lines, both climb and bull, are low stretch static lines. Most have 50-70 less stretch than kernmantle static line.
> 
> So, do not fall fall on arbo line, it might hurt. But the limited stretch should save your hide, as opposed to the near zero stretch of synthetic fiber high tech lines like Spectra, kevlar, and Vectran *




Say what??


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## Lumberjack (Feb 14, 2004)

RB, I still don't understand where you get that static kernmantle ropes are more strechy than arbo lines.

You got a site or something with the info on it?



Carl


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## RescueMan (Feb 14, 2004)

*Rope Stretch*



> I still don't understand where you get that static kernmantle ropes are more strechy than arbo lines


The National Cordage Institute defines three categories of rope according to their stretch characteristics:

Dynamic - >10% @ 10% MBS (= 1 SWL) 
Low Stretch - 6-10% @ 10% MBS (= 1 SWL) 
Static - <6% @ 10% MBS (= 1 SWL) 

The stretch characteristic of arborist rope varies considerably from the relatively stretchy NE Safety Blue to the very static 32-strand double-braid (about 1%).

Paolo Bavaresco in “Landscaper” magazine 2000, writes: "Don’t choose a rope that mimics Steel or Bungee properties! Under no circumstances should high strength fibres like Kevlar be used as a climbing or rigging line. It requires very high bending radii to operate safely, and has extremely poor energy absorption properties, therefore eliminating its safe use in any operation other than pulling! High stretch ropes will not provide sufficient control in close proximity to targets. Stretch in a rope is not recoverable after severe shock loading – it will stay stretched rendering it useless for energy absorption. Loading a braided polyester rope over 40% of breaking strength will result in permanent stretch (damage)."

see: 

SELECTION AND USE OF ARBORIST ROPE 

- Robert


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## NeTree (Feb 14, 2004)

yea... but who climbs on DOUBLE BRAID?

When I said "Low Stretch", I was referring to static line in relation to climbing line. I should have said "no stretch".

I was comparing "static lines" in relation to arborist CLIMBING lines in specific.


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## Lumberjack (Feb 14, 2004)

I have climbbed on super braid before, and it really wasn't that bad, I liked the lack of strech for work positioning, but it would be a bugger on a fall. I also will repel down it, so I don't have to use another method of pulling my climbing rope down.

I also remember someone on here saying that super braid was the rope of choice for a climning rope.

Carl


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## NeTree (Feb 14, 2004)

I dunno, I've tried all kinds of line, and I still like Safety Blu HI-V best. Maybe I'm just ATTACHED....

get it?



attached?


HA! I crack myself up!


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## Stumper (Feb 14, 2004)

BradleyFord, I have read this thread with interest but I understand Brian's frustration with your question. Slippage in a friction hitch does not equate to failure. One of the theoretical benefits of the V.T. is the fact that it can be expected to slip at 800-1200lbs of load(dependent upon cordage diameter and material). The theory is that slammming a V.T will result in a shock absorbing slippage without breaking the rope or (hopefully not) killing the climber. You'll have to look a while to find anyone who has tested the theory though!. If any friction hitch controls the climber and his gear without slipping during normal use then it is an adequate /safe hitch. A study comparing the point at which various hitchs slip would be useful but looking for the hitch that will support 2000 lbs without slipping is looking at the wrong end of the spectrum for maximum safety. The hitch that slips at just a little more than the climber's weight is the "safest" in the event of a fall since it will absorb the shock by slipping. As Brian has pointed out-good tree climbing techniques preclude setting oneself up for a free fall so in the final analysis whatever holds us in normal use makes the grade.


I think that Mike Maas reported testing an Open Prussik/Improved Tautline To 4000lbs a couple of years ago-The only friction hitch that didn't slip at around 1000lbs of those tested--but I may be remembering incorrectly or Mike might have had that hitch aroud our legs.


RB, I think that you may have confused things a bit. Dynamic kernmantle is very stretchy. Static kernmantle is very stretch resistant-it varies but the numbers are very small for 200-400lb. loads. I have read references to Arbo lines as "Semi-static". They stretch but not a lot. I agree that falling onto slack lines is a very bad idea.


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## Kneejerk Bombas (Feb 14, 2004)

An interesting thing that happens with a prussic is the more weight applied, the tighter it grabs. Then, the more pressure it takes to break it loose. 
That's why JPS (350 lb.s) and Kenny (90 lb.s) can both climb on the same set up and it will work great for both. 
When we climb on a doubled line, the hitch only takes a small percentage of our weight, and works great. Install a friction saver and things start getting tighter, hitches grab more and are harder to release. 
Try the same hitch on a single line and it grabs and holds, but you can't get it to slide, and if you do, it burns and is hard to control. 
To hold and control 2000 lb.s would not work with a rope hitch. Now, if you just want it to handle a fall, a prussic will slip if it encounters a 2000 lb. load, then grab once the shock is ended.

I did do some pulling last year on a few different prussic hitches on arborist ropes, the results were interesting, but most importantly they all started to slip at some point, they don't hold until the line breaks.


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## Bradley Ford (Feb 17, 2004)

> _Originally posted by RockyJSquirrel _
> *You have yet to explain why you find it imperative to have a hitch capable of LOWERING 2000 lbs on a static system (or is it a dynamic system today?).*


I do not find it imperative to find a "2000 lb." hitch; in fact I'm open to the possibility that such a hitch would not be safe (referring to my next post). I would like to objectively define a "safe" hitch with a set of criteria that each hitch could be measured against. Such criteria would allow one to judge hitch A safe to use, or hitch A safer than hitch B. The criteria should be applicable to both dynamic and static rope climbing systems. I added "descent" to the thread title because I'm not as interested in hitches used only for ascent.


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## Bradley Ford (Feb 17, 2004)

> _Originally posted by Mike Maas _
> *A good hitch would run when overloaded, then slowly grab, to reduce shock loading in case of a fall. *



Does a "safe" hitch have a maximum weight holding ability so that by slipping it can help absorb some of the shock load from a fall? How would this maximum weight be determined?


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## RescueMan (Feb 17, 2004)

> Does a "safe" hitch have a maximum weight holding ability so that by slipping it can help absorb some of the shock load from a fall?


This is exactly the reason that tandem 3-wrap prusiks have become the belay of choice in the rescue community (for handling up to 600 lb loads and the possibility of some shock loading).

Mechanical rope grabs have been shown, in drop testing, to severely damage or sever a static kernmantle rope. Prusiks - which tend to slip and then heat up, partially melt and grab - can safely catch a 200kg load in a facter 1/3 drop (1 meter drop on 3 meters of rope). 

But the weight-holding ability of a prusik (or any other hitch) depends on the type of cord and type of rope used (both the material and the "hand" or stiffness), the relative diameters of the cord and rope, whether the host rope is new or used, wet or dry, etc...



> How would this maximum weight be determined?


By carefully controlled static pull testing and dynamic drop testing with various combinations of cord/rope.


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## Kneejerk Bombas (Feb 18, 2004)

> _Originally posted by RescueMan _
> *
> 
> By carefully controlled static pull testing and dynamic drop testing with various combinations of cord/rope. *



And here is the problem, there are almost infinite numbers of possible combinations of ropes, sizes, hitches and weather to be able to say such and such hitch reacts this way when loaded. 
Perhaps the best way to figure it out is to find the combination you like to use, then test it.


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## NeTree (Feb 18, 2004)

Not to mention contaminants such as oils from your hands, dirt, etc. 

Sounds like a cool project for MythBusters!


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## knudeNoggin (Feb 21, 2004)

> I haven't seen any test data on arborist hitches,
> but of all the rock-climbing hitches,

Let's be careful here: what's "all"? --name names! E.g.,
was the 2-wrap Hedden H. tried? --how about a 3-wrap one?
(You can see that this is an infinite progression, going
well past practicality, yes, but not initially.) And how
about the series of reversed Half-Hitches, as shown and
briefly discussed on Gary Storrick's site?! Cf.
http://storrick.cnchost.com/VerticalDevicesPage/Ascender/AscenderKnots.html

The point is: there is much "information" about knots about that has the form
"is the strongest ..." which fails to describe the universe of knots that have
been considered--which might turn out to be few!

> the [P]rusik can control the most weight (as much as 2300 lbs
> in some applications), with a 4-wrap Bachman[n] close behind,
> and the autoblock and kleimheist down at 400-600 lbs. 

How about using some friction hitches in sequence?
(But given the heat generation for a really big load such as 2000#, one might
want them to be of Vectran or even a more heat-resistant aramid!)

> You keep touting technora and vectran, ...
> In rescue, these fibers are generally verboten. Independent test results
> for all the high-strength cords, presented at the 2000 International
> Technical Rescue Symposium, showed that there is nothing better than good
> old nylon rope.

Was polyester among the fibers tested? (no, not if you're thinking of Moyer)
Actually, in the marine world, there is much use of poly-combo/"Poly-DAC" ropes.
Among the various sorts are those in which the PS surrounds core PP fibers
(and arborists have some like this). I should think that some of these, which
have both flexibility but also some bit of *spring* might serve well in friction
hitches, where the spring would help on release. (But I've not played around
much w/them.)

> While Technora, an aramid like Kevlar but without the self-abrasion problem,
> is significantly stronger than nylon in tensile strength, Vectran, a
> liquid-crystal polymer, is actually a bit weaker.

Whoa! --no way, maybe not even after flexing (though that's an open issue).
It is simplistic to call the cords tested by Moyer "Technora", "Vectran",
"Kevlar/Spectra", "Spectra", because they are kernmantle constructions with
these hi-mod fibers limited to the core, which is a fraction of the rope size.
AND, the cord size was smaller than the nylon cord's size. So, you're comparing
the apple-y Sterling 7mm nylon kern (where core and sheath both provide strength!)
to the orange-y Sterling Nylon-sheathed Vectran (where core alone provides the
strength, unless it's slipping internally to load the sheath--something that
does happen and isn't always recognized by test reporters!). So that's about
a 6/32" Vectran (or less) vs. 11/32" nylon. Moreover, it's just ONE test.
(That said, a striking result was that the Sterling Vectran-cored cord broke
at less than its advertised loop strength (strength of a sling made by tying
ends w/Grapevine or Triple Fisherman's is of common relevance to climbers
--nevermind the nominal tensile of material)! I think that Sterling and other
climbing cord vendors are avoiding Vectran, now.)

(For a good overview of the history of synthetic cordage fibers, see the
impending book _The Outdoor Knots Book_ by Clyde Soles (Mountaineers Press),
due out ca. April.)

> And, while nylon weakens only 8% with a figure-8 knot in it,

Robert, you elsewhere sling about CMC's test data, also for nylon, so note
that their Fig.8s weaken at about double this figure!? (And the 70-80%
range for the knot seems a pretty common reading--though one never knows
1) how the knot is tied & loaded, and 2) how pure tensile was determined.
(Moyer, e.g., did his own testing, of 5 samples for everything; his images
of the actual Fig.8 knots--he tied top one way, bottom knot another--aren't
entirely clear, but seem to be of a non-symmetric form; his data, however,
are remarkably similar, with a std.dev. approx. 100#.))

> Vectran and Technora weaken by 48% and 40% respectively

These precise results are for one testing of a few samples of particular ropes.

Here, again, note that we're talking about core components of a cord; one
might conjecture that pure hi-mod will be weaker, yet. Indeed, in an article
for SAIL mag., Brion Toss reported testing of hi-mods in which the highest
figure of any knots--and this was for a hitch--was about 45%; the Bowline
got no higher than 27% or so. However, his report leaves many questions
(such as Why didn't you test a Dble.Bwl and a Fig.8 loopknot?); e.g., I
tried to get the slippage in a Bwl he asserted obtained at about 15% in
Vectrus (Yale), and with a (???? skinny!) "1/4-inch" rope and a 5-to-1
pulley, bouncing my 180#, I could see no threat of slippage!? YMMV ?
(5 x 180 = 900 = 25% of 4500, approx. nominal tensile) Brion's results
seem dubious in light of those by Moyer and others (and even some of the
laughable Practical Sailor copycat testing (Prac.Sailor Sept.2001) suggests
quite different results).

> Paolo Bavaresco in "Landscaper" magazine 2000, writes: ...
> Loading a braided polyester rope over 40% of breaking strength
> will result in permanent stretch (damage)."

This is contradicted by an Oil Companies Int. Marine Forum (OCIMF) break-test
method which stipulates that a rope be cycled ten times to 50% of its
estimated breaking strength before stretching it to rupture--the cycling is
done to ensure that fibers are settled, as a sort of acceleration of the
normal in-use conditioning. This process tends to reduce data scatter
(as opposed to testing uncycled new rope). [Cordage Institute tech.man.]

> And here is the problem, there are almost infinite numbers of possible
> combinations of ropes, sizes, hitches [and how they are drawn & set!]
> and weather to be able to say such and such hitch reacts this way when loaded.

This is a key point. But, it might be that some careful analysis of hitches and
close variations, and the slight or greater changes in behavior, can reveal some
helpful principles. E.g., Heinz Prohaska, (1st) originater of the ProhKlem Hitch,
aka (Jason) Blake's Hitch (HP pub'd in '81 & '90; Blake in '94), advises to add
an extra lower wrap to improve gripping in stiff Prusik rope if it otherwise slips,
and to add a turn at the top end (which turns around only the object rope) if the
slippage is attributable to load alone. Given some guidance by principle, then
perhaps the vast array of possible test cases could be traversed by intelligent
sampling (doing fuller testing here or there only when sample results didn't
fall within expected ranges). (This is a problem for more than friction hitches.)

Knotting seems fertile ground for myths.
I hope to cut through a lot of them.

Cheers,
knudeNoggin*


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## Eagle1 (Feb 21, 2004)

WOW


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## Stumper (Feb 21, 2004)

What Eagle said only spelled backward-WOW.


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## NeTree (Feb 21, 2004)

Welcome to the site, Noggin'.


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## RescueMan (Feb 21, 2004)

*Myths?*



> Knotting seems fertile ground for myths. I hope to cut through a lot of them.



knudeNoggin,

Cutting down other's research is easy. Building up useful information and data on rope and knot characteristics is a much larger challenge, and your lengthy obfuscation doesn't contribute to that.

All test data has a limited scope and applicability. Good researchers (such as Moyer) indicate those limitations and offer their results as pieces of a larger puzzle.

Taking the puzzle apart and scattering the pieces doesn't help anyone's understanding.

How about contributing something positive to the discussion, rather than just tearing down what you consider to be "myths".

- Robert


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## knudeNoggin (Feb 25, 2004)

> How about contributing something positive to the discussion,
> rather than just tearing down what you consider to be "myths".

RescueMan, save us--toss us a line! What in the world are you saying?
My msg. was pretty clear, and, to my thinking and I think others' too,
a contribution that shed light on this topic; so, you'll have to help us
understand how you see it as "obfuscation"!?

> Cutting down other's research is easy. ...
> Taking the puzzle apart and scattering the pieces ...

Huh? First of all, research is intended to be examined and, if found
wanting, cut down (like a bad tree that might otherwise lead to injury).
And if it were so "easy", there'd be less bad research & other nonsense
published (we should hope). Rather, it seems that most people are lazy
and willing to accept conclusions w/o scrutiny. In the realm of knots
and cordage, this seems especially true. Otherwise, how could something
like the Practical Sailor issue (Sept'01) stand the light of day? How
could knot books repeatedly put forth the things they do--errors not
only not corrected, but copied!?

You made some quite particular assertions about materials & knots,
some of which were clearly wrong (Vectran weaker than nylon), and
others that needed some perspective (Fig.8 loopknot weakens nylon
by (only) 8%). So, I contributed information to improve understanding
(such as CMC's test results showing the Fig.8 reducing by 18%, and I
might add the Lyon report (of three static & one dynamic kernmantles)
range of 23..34%. How is this obfuscation? --or scattering of pieces?
Perhaps in that neither CMC nor Lyon tested hi-mod ropes, to have
their take on that (maybe they'd have shown reductions more severe
than did Moyer?!) Well, I did cite the Sail issue's test report on the
quite severe results, though that article was less than overwhelming
with data. But a key point was to see that one can find quite different
figures out there, and just pulling out one that seems to suit you is
less than playing fair (in your challenge to Nick's championing hi-mod
stuff (though he has in other situations taken the low-tech side )).

As for "cutting down", removing deadwood IS positive. Consider the
Lyon report (www.hse.gov.uk/research/crr_htm/2001/crr01364.htm)
and its assertion/conclusion about the relative strength of the
Overhand loop's two possible loadings; Lyon says "In all cases,
failure occurs ... wher the loaded rope first rounds the loop.
Whether it rounds the loop above or below the loose end can
affect strength by up to 10%. In the overhand knot, it is stronger
if the working rope lies above the rope end." We can wonder what
"above"/"below" mean, but a natural interpretation would be that
if the loaded part lies above the end, it bears against it (rather
than pulls away from it). We can also remark at "by up to 10%":
the natural interpretation in this context is "10 percentage points"
--something easily seen in result figures (as opposed to 66% vs.
60%, it would be 66 vs. 56). In any case, in the appendix with
test data, Lyon's wording is "live rope on {top/bottom} as it
entered the knot"--which I'd take to equate "top" with "above",
etc.. But in that case, their data if anything give a contrary
conclusion, with "on top" cases having a slight edge. Here's
their results, converted to percentages; they tested the loops
with knots on both ends, two specimens having the same of
whichever orientation (on top or on bottom), and the middle
case one of each(!). For the 3 low-elongation & 1 dynamic
ropes they got:
66-69-68 ; 64-60-66 ; 59-59-62 ; 59-59-63
Now, should we let this stand w/o question? I don't see
either the bias for the stated orientation (but there is some
dubious description in terms), and certainly don't see the
"10%" in any sure way! And with so few test cases, there
really isn't good ground to stand on in drawing conclusions.

knudeNoggin


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## Tom Dunlap (Feb 25, 2004)

Knud,

Can you direct me to more information about this:

E.g., Heinz Prohaska, (1st) originater of the ProhKlem Hitch,
aka (Jason) Blake's Hitch (HP pub'd in '81 & '90; Blake in '94), advises to add
an extra lower wrap to improve gripping in stiff Prusik rope if it otherwise slips,
and to add a turn at the top end (which turns around only the object rope) if the
slippage is attributable to load alone. 

If you want to email me off forum that would be great.

Thanks,

Tom


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## Bradley Ford (Feb 25, 2004)

Based on feedback from Mike Maas and RescueMan, a safe hitch should slip (and then grab when the load is sufficiently reduced) at some shock load to help prevent injury. Can this shock load be defined relative to Joe Climber's weight? For example, is it reasonable to suggest that if, after all load absorbing effects have occurred, the remaining load is (this percentage is just made up) 150% of Joe Climber's weight, his hitch should slip to prevent Joe from absorbing any more of the shock load? If so, what is a safe percentage?


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## Lumberjack (Feb 25, 2004)

I would say 3x's the weight of the climber, possibly 4. At only 1.5x's his weight, the hitch would slip too much, IMO. 3-4g's is a good number IMO, alowing some stiff stops (repeling, or parachuting to a spot on the tree) but it isnt enought to hurt the climber.


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## RescueMan (Feb 25, 2004)

The "limit of survivability" for a human body is considered to be 12 kiloNewtons (2650 lbs. force). Dynamic ropes are required to limit maximum shock loads to 12 kN, and long falls on dynamic rope generally do not generate more than 9 kN (about 2000 lbs).

The actual shock load on the climber depends on the fall factor (the distance fallen divided by the amount of rope available to absorb the shock), the modulus of elasticity of the rope, and the amount of intermediate friction or dyamic slippage in the system.

Just bouncing on a fixed rope can create 2g's of force (double the climber's weight). A fall factor of 1 (e.g. falling 5 ft on 5 ft of rope) on static rope can generate 15 g's of force.

I'd agree with Lumberjack that a hitch should be able to hold 3-4 times the climber's weight if it's going to absorb the usual bouncing of ascending. And that would still be well within a safe zone for shock load to the climber.

- Robert


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## Bradley Ford (Feb 26, 2004)

A safe hitch should start to "slip and grab" when loaded with a 4g shock load. So for 200 lb. Joe Climber, a safe hitch slips at 800 lbs., but for 50 lb. Joe Jr., a safe hitch slips at 200 lbs.



> _Originally posted by Mike Maas _
> *That's why JPS (350 lb.s) and Kenny (90 lb.s) can both climb on the same set up and it will work great for both.
> 
> *


If a safe hitch is dependent on the climber's weight, will JPS and Kenny require different hitches in order to both be safe? Or will the same set up slip at 4g's for both 350 lbs. (at 1400 lbs.) and 90 lbs. (at 360 lbs.) due to the actual load difference?


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## Lumberjack (Feb 26, 2004)

> _Originally posted by Bradley Ford _
> *A safe hitch should start to "slip and grab" when loaded with a 4g shock load. So for 200 lb. Joe Climber, a safe hitch slips at 800 lbs., but for 50 lb. Joe Jr., a safe hitch slips at 200 lbs.
> 
> If a safe hitch is dependent on the climber's weight, will JPS and Kenny require different hitches in order to both be safe? Or will the same set up slip at 4g's for both 350 lbs. (at 1400 lbs.) and 90 lbs. (at 360 lbs.) due to the actual load difference? *



I would doubt it. I would require a different number of wraps and crosses (VT and such). The added weight would make some difference in the amount it grabbed, but not enough to take the climbers weight, so a variation would be required.


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## TheTreeSpyder (Feb 26, 2004)

> _Originally posted by Mike Maas _
> *.....That's why JPS (350 lb.s) and Kenny (90 lb.s) can both climb on the same set up and it will work great for both. ...
> *



Jest when ya think ya squeaked by, i'm catching up on mah'reading!! After the line about thighs as huge as my waist, m'Lady and i been wondering about an ol'pair of his Levi's for a dual sleeping (mostly) bag......

Fantastic thread, surely a "5" on the ratings!! One view might be to inquire why someone can ride a friction hitch on a DdRT; yet it jams on someone half the original climber's weight on an SRT.

Part of the stabilization of a setup over differnet weight ranges might be in the stabilization of speed in 2 falling logs of different weight, yet hitting the ground at the same time. The heavier one hits harder, because it has more raw force potential; but yet does not acces that to speed up. IMLHO, that same weight that gives it the heavier log/body more force; also takes more force to move/change speed; so the 2 items bound as principals (more force yet more reluctant to change)invoked by the weight cancel each other out (assuming same shape/air resistance, wind etc.); and the 2 items fall at the same speed (?)

i think that the most clear point is that there are a lot of things going on, in directions and views that surprise most all and have lead to lots of thinking ! Just more reasons for keeping the requirements for strengths etc. high; just bumped up some to cover everything etc. In the same spirit as they have been handed down to us. Knowing that whatever is said and written; variations, mistakes etc.; and someone outrightly just going with less than is said everytime. The guidelines set should cover all these things and still have safe ranges i think.

The fancy fibers and their stiffness etc. have yet to prove themselves to me; many i think are weak on the bend. Like some super carbon fiber threads that can hold tons, yet can be snapped easily by hand once tied in a Knot . But, then i don't burn out chords and tails descending...............

RescueRob (et al)- How much more strength do you quote on a double bowline w/Y tie off? And on hitches whose strength would be dependant on host item; when that is a carabiner; does that tilt things towards 8's and bowlines causing less interuption in the line? What of (i guess ) the "Stevedore" and + of an '8' brought to a '9' or '10' (?) strengthwise; and the strength loss in arching the wrong way with that strategy? 

Enquiring Minds Knead to Know!
:alien:


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## Bradley Ford (Mar 1, 2004)

> _Originally posted by Bradley Ford _
> *A safe hitch should start to "slip and grab" when loaded with a 4g shock load. *


Has anyone tested their climbing system for this functionality? How did you do it?


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## Bradley Ford (Mar 5, 2004)

Do all hitches slip in response to a shock load? Do the Tautline and Blake's hitches slip or do they just grab? Do all of the French Prusik family hitches slip?

Can all hitches be categorized into either "slips and grabs" or "just grabs" in response to a shock load, or are there other responses to consider? (Careful with those "just slips" hitches.)

Is a properly configured "slips and grabs" hitch inherently safer than a properly configured "just grabs" hitch? Or is it vice-versa?


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## RescueMan (Mar 5, 2004)

> Do all hitches slip in response to a shock load?



All hitches slip, not just in response to a shock load but whenever the load exceeds the friction of the hitch on the host line. And the friction of any hitch on a host line depends on the composition, the stiffness, the texture, the size, and the surface condition (new/old, wet/dry/frozen, coated/uncoated, etc.) of both the hitch cord and the host line.

The results of slippage depends on the extent and the speed of the slippage. The sudden dramatic slippage from a shock load can cause melting of the hitch cord (the host rope is moving through the hitch and so does not overheat at any one point) and consequent fusing to the host or possible failure of the hitch.

The friction capacity of any hitch/host combination will vary from the low of a Munter hitch (about 600 lbs. force) to the high of a 3-wrap prusik (up to 2400 lbs. force).

I suspect that most of the arborist climbing hitches would have friction capacities toward the lower end of that spectrum.

- Robert


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## knudeNoggin (Mar 8, 2004)

> _Originally posted by Bradley Ford _
> *Do all hitches slip in response to a shock load? Do the Tautline and Blake's hitches slip or do they just grab? Do all of the French Prusik family hitches slip? ... *



FYI, check out: http://cmru.peak.org/Rigging/july97_drop_test.htm

knudeNoggin


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## RescueMan (Mar 8, 2004)

*Another Correction*

knudeNoggin,

That link shows an interesting drop test, the only one I've ever seen that included the dog-n-tails (similar to the VT hitch but with just braids).

However (and here's the editor in me again), there's a typo on the picture for drop test #10 which indicates "wet" when the chart correctly identifies that test as "dry".

I emailed Corvallis Mountain Rescue a while ago to find out which condition was correct. They said the chart is the one to go by.

- Robert


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