Extending a Cam Sling: Sling on Sling   May 21, 2007

Now this is just me—when I rack for a multipitch trad climb, I rack like this:

• Cams (with a biner on each cam), set of stoppers on my harness
• Quickdraws and a few spare biners on my harness
• Over-the-shoulder runners with one biner on each—over my shoulder (well duh...)

If I need to place a cam, I grab one, place it, clip it and go.

If I need to place a cam and extend the sling, I place a cam—then either use one of my quickdraws and clip through the sling like this:

Or grab a shoulder sling and extend all the way like this:

Not rocket science.

FYI: if I place a stopper I either use a quickdraw, a shoulder sling with the biner that’s on it PLUS a spare biner, or a quickdraw AND a shoulder sling for extra length.

So a while ago when I was down in the desert climbing a tower with a buddy, and I came up to several cam placements like this—I was confused.

  

I saw him fiddling at all of these cam placements and was wondering what in the world was going on up there—he’s taking forever farting around with gear—maybe it’s because he’s so strong he doesn’t get it—but for me, I need to place the piece and keep moving before I flame out. So as I’m seconding his pitches and having to deal with this unfamiliar conglomeration of slings on slings on cams, etc—I’m wondering:

• Why is he doing this? and
• How much does this affect the strength?
• And, I am getting pumped out of my mind.

I mean nylon on nylon or Spectra on Spectra, etc—sounds like bad juju to me—and I’m not talking about girth hitching anything here—just looping it through…

I get to the belay and ask my partner what’s up with the method—and then it all clicks—ahhhh "old school alpinist," light is right, save a biner, etc, etc—and old habits are hard to break.   Regardless—I got back from the weekend, explained the situation to the crew in the QA lab and we proceeded to do a few quick tests.

The Tests

We slung some 8 mm Spectra through a typical cam sling and did a few pulls in the tensile tester and a few drops in the drop tower. We compared the results to a cam sling only. 

Here are the results:

Tensile Tests:

15.6 kN

16.2 kN

15.5 kN

Average: 15.8 kN

Actual historical average for cam sling ONLY: 25.5 kN

Therefore sling on sling method provided results 61.8% of historical average—or another way to look at it, it reduced the strength of the cam sling by almost 40%.

Drop Tests (note: these are NOT UIAA drop tests)

In both test configurations (i.e. cam sling only, and cam sling threaded with 8 mm spectra), the rope broke after over six successive factor two drops (80 kg mass) with peak loads of over 10 kN.  The cam sling, or sling on sling method was NEVER the failure mode in drop test scenarios.

Conclusions

The sling on sling method of extending a cam sling does save the use of a biner but in my opinion is cumbersome for both the leader and the second. It also appears to reduce the ultimate strength of the system, however, in most cases not so much as to be the weakest link in a real-world climbing situation. 

Bottom Line

When you’re extending a cam sling, use a biner and make everyone’s life a bit easier. If you’re a super light-and-fast type of guy, the sling-on-sling method works, but know that it does weaken the system. Also note that none of the tests we performed took into account possible wearing from rubbing and friction—possibly even reducing the overall strength of the connection even more.

Climb Safe,

KP

March 9, 2007—Girth Hitching a Stopper

A buddy of mine emailed me the other day—he was out at a crag and saw someone girth hitch a #4 stopper to a bolt hanger, then clip a biner to the end, clip his rope and continue on. Hmmmm?? Maybe short a biner? Not sure. Regardless—he asked if I could do a quick test just out of curiosity to see how strong it would be.

We did a few pulls in the tensile tester. Note: Due to the way the particular bolt hanger we used was stamped, one edge was slightly rounded, whereas the other was definitely more sharp (see photo)—therefore we girth hitched the stopper both ways, getting data with the load bearing strands on the rounded edge AND on the sharper edge. (see photos)

We tested three samples in each configuration. Here is a summary of the results:

Tensile Tests

Test configuration	Average
Load strands over rounded edge	1845 lbf (8.2 kN)
Load strands over sharp edge	1270 lbf (5.6 kN)

Note: Just for reference—a #4 Stopper is rated to 6 kN (1349 lbf); and a quickdraw typically is rated to 22 kN.

Drop Tests

We decided to perform similar tests (i.e. load strands over the rounded edge and load strands over the sharp edge) but in a dynamic (i.e. drop) scenario. The results were very similar:

Test configuration	Value at Failure
Load strands over rounded edge	1755 lbf (7.8 kN)
Load strands over sharp edge	1424 lbf (6.3 kN)

Observations  & Conclusions

• The way the stopper wire was threaded had a significant impact on the ultimate strength of the system (variation of approx. 30%).
• Similar results were found in tensile tests and dynamic tests.
• Significantly weaker than if a proper quickdraw was used (approx 30% of “full strength” (i.e. 22 kN).
• Girth hitching a stopper to a bolt hanger results in a system strength such that the loads at which these set-ups will fail are within the loads that can be seen in real climbing situations in the field.
• It most definitely is possible that if the climber in question here had whipped onto that bolt, the stopper wire could have cut and he/she would have plummeted to the next piece. 

Bottom Line

Sometimes if you’re in a situation, you do whatever it takes—because sometimes “something is better than nothing.” I’ve used my gear sling to girth a shrub, clipped my ice tool and left it there as my last piece as I’ve topped out, stuffed a knotted sling and even a carabiner into a crack as a stopper as well as a host of other not-so-smart-but-in-times-of-desperation-perhaps-better-than-nothing things. I’ve heard of guys rapping off of boot laces, using tent poles as a dead-man to rap off of and even jamming a camera lens in a crack using it as a chockstone to bail off a route. The reality is that sometimes you do what you need to—but in most cases this is not necessary, and gear should be used as it is intended, otherwise the strength, and ultimately your safety, can be compromised. 

Use carabiners when clipping to a bolt, or between a cam, piton or stoppers and slings. Clip your rope through a carabiner, never through a runner. Don’t girth hitch stoppers to bolts, slings to bolts, slings to stoppers, or even slings to slings, etc. Understand how to properly use your gear, read the instructions and seek instruction from a qualified guide if you are unsure.

Climb safe out there,

KP

January 19, 2007—Retiring Old Ropes

We’ve all seen it at the cliffs, and I’m a major offender myself—climbing on old ratty ropes. Yeah, ropes are expensive and that’s the main reason people push their ropes to the limit—trying to squeeze every last ounce of use out of them until they become a dog leash or door mat. I’m not going to lie—I get sweet deals on cords, but still, I don’t like to be wasteful and usually end up climbing on my ropes a little too long.

Ropes can develop a sentimental value to some people—maybe it’s the cord you sent the “proj” with, or had a great trip up a Valley wall with—so you just don’t want to retire it. I had such a case—a special 9.4mm. I kept climbing and climbing and climbing on it. It was beat. It started out as a 70 m, then after endless days of constant whippers, it became a 65 m, then 60 m, then 55 m. I just didn’t want to see it go. 

So one weekend I was taking REPEATED MONSTER whippers off the VERY LAST move of one of the many nemesis routes of mine. I had to skip the last clip because I’m too weak to clip it—and go for a huge chuck to the finishing bucket. I would sail onto the end of my trusty 9.4 mm time and time again. The last 10 ft or so of the cord were absolutely throttled—at the end of that weekend, it was time to say goodbye.

Of course, I brought it into the lab and figured I’d do some testing.

Testing

I decided just to test the ultimate tensile strength of the rope in different areas, and compare it to a brand new rope of the same model and make.  We didn’t do anything fancy—just a figure 8 on each end, and pulled to failure in the tensile tester. We were just doing this quick and dirty for comparison's and curiosity's sake.

When tested like this, breakage at the knot is almost always the failure mode—and remember—figure eight knots can reduce the strength of a rope somewhere in the neighborhood of 25-30%.

Results

The first test we did was a piece from one of the totally worn-out ends. It broke at around 6 kN—and NOT at the knot.

Yowsa, I had just been whipping all over the place on that cord—and it broke at 6 kN, and NOT at the knot—scary stuff. Though the sporto falls I was taking were super soft (my wife was belaying and is light, and I am fat)—chances are the tension seen in the rope wasn’t anywhere near 6 kN, but if I had gotten slammed hard, low to the ground, etc??? It’s definitely possible to see these kinds of loads in the field.

We decided to do more tests on my cord—on the ends, and in the middle, as well as on a brand new 9.4 mm for comparison purposes. In all subsequent tests, the sample broke at the knot as expected, but we still saw some frighteningly low values.

New 9.4 mm	KP’s 9.4 mm middle	KP’s 9.4 mm end
15.6 kN	9 kN	6 kN*
13.8 kN	9.8 kN	8 kN
		7.7 kN

*broke in the middle of the test sample

We tracked down another beat 9.4 mm from one of the QA guys—and put it through the ringer as well:

New 9.4 mm	Used 9.4 mm middle	Used 9.4 mm end
12.9 kN	11.9 kN	8 kN
13.6 kN	11.9 kN	9.8 kN
	11.6 kN	8.6 kN

Still curious and given the results we’d seen—the boys in the lab and I decided to do the same with some other tattered ropes that were around.  We did similar tests with more Beal ropes as well as Sterling, Edelweiss, Mammut, etc.  We found very similar results:

• The worn out, frayed, end pieces of any rope we tested were consistently significantly weaker than the middle sections of the same cord.
• We DID manage to find other samples that broke in the middle (as opposed to at the knot) – and at relatively low loads—less than 7kN.
• The end pieces, and middle pieces were consistently weaker than a section of a brand new cord.

Bottom Line

• Ropes, like all climbing gear, don’t last forever—the ends of your rope take a beating—be wary of super frayed, worn, puffed out, beat up tattered cords. Yes, ropes aren’t cheap, but they’re also your lifeline—literally—so take care of them.
• When the ends of your cord get all beat and tattered from dogging up routes, cut the ends off, or a buy a new rope.
• I always cut equal lengths off BOTH ends so the middle mark is always in the middle.
• Be sure to mark the new length on BOTH ends so you and your partners know what you’re dealing with.
• And while you’re at it—tie a knot in one end—too often you hear of someone being lowered off the end of their rope—definitely not cool.
• For me the most important thing… to train harder and get stronger, so I won’t be whipping in the first place.

Be careful out there,

KP

 

December 18, 2006 “Is my rope still OK to use if I accidentally peed on it?”

It’s almost disturbing how many emails I get with the almost identical: “Uhhh, hmmmm, I kinda peed on my rope, do you think it’s still ok?,” or “A dog peed on my rope at the crag, should I retire it?,” or “My girlfriend peed on my rope, is it still ok to use?”

I hate to sound like a broken record, but when this sort of thing happens, no one can be exactly sure what effect it had on your rope or equipment. I always have to play the conservative card and say, “If in doubt, retire it.”

Other than wondering what actually is going on out in the field with all of these people peeing on each other’s ropes, I wondered what kind of affect does it really have. No, I didn’t go pee on a rope of mine and test it, but as "luck" would have it, I got an email from a person something to the effect of:

“My cat peed on my brand new 9.1 mm, it sat there for over a week, when I got home to discover this I washed it several times in baking soda to get rid of the smell, and I have two questions for you:

• Is the rope ok to use?
• What kind of hat should I make out of my cat? Note: he really did ask this…

I had the guy send the now non-stinky rope in and we performed some tests on it.

So again, of course, by no means are these experiments conclusive—just some interesting information if you happen to have a cat pee on your brand new rope and then wash it in baking soda three times.

The Tests

We performed all tests on the ‘Cat Pee’ rope alongside a baseline test of a brand new 9.1 mm of the same brand—so that we could compare relative results.

Static Tensile Tests

• Full Strength—Pulled five samples of each rope in tension in the tensile test machine—ropes wrapped around drum jigs to force the failure mode to the single strand.
• Strength over a Carabiner—Pulled two samples of each rope in tension in the tensile test machine—over a carabiner—using figure 8 knots on each end.

Drop Tower Tests (note: these tests are not in any way even close to the UIAA drop test)

• 4 ft length of rope—figure 8 knots in each end—factor 1.35 fall—over a carabiner
• 8 ft length of rope—figure 8 knots on each end—factor 1.2 fall—over a carabiner
• 4 ft length of rope—figure 8 knots on each end—factor 2 fall—direct onto anchor
• 8 ft length of rope—figure 8 knots on each end—factor 2 fall—direct onto anchor

The Results

Tensile Tests

In all cases the failure mode was the rope breaking at the fixture. So this isn’t a totally accurate test as the desired mode would be the sample breaking in the middle, however, for our purposes it does give us a relative comparison to some extent.

• Full Strength Test—The ‘Cat Pee’ rope averaged approximated 94% of full strength of a brand new rope.

~Full Strength
Joker 9.1		Joker w/ Cat Pee
	Strength (lbf)		Strength (lbf)
1	4739	1	4329
2	4361	2	4058
3	4547	3	4362
4	4421	4	4373
5	4671	5	4295
		6	4285
avg.	4547.8	avg.	4283.7
% full	100	% full	94.2

• Over a carabiner—The ‘Cat Pee’ rope averaged approximately 95% of the strength of the brand new rope.

Strength Over Carabiner
Joker 9.1		Joker w/ Cat Pee
	Strength (lbf)		Strength (lbf)
1	6406	1	6014
2	6324	2	6081
avg.	6365.0	avg.	6047.5
% full	100	% full	95.0

Drop Tower Tests

• 4 ft length of rope—figure 8 knots in each end—factor 1.35 fall—over a carabiner.

New Joker 9.1 mm		“Cat Pee 9.1 mm”
# Falls Held	Max Load Seen	# Falls Held	Max Load Seen
14	3968	9	3982

Factor ~ 1.35 over a BD Airlock2
Joker 9.1		Joker w/ Cat Pee
Drop	Max Force (lbf)	Drop	Max Force (lbf)
1	1411	1	1680
2	2264	2	2402
3	2699	3	2972
4	2968	4	3265
5	3189	5	3446
6	3336	6	3681
7	3458	7	3748
8	3572	8	3895
9	3570	9	3982
10	3698	10	3239 X
11	3765
12	3870
13	3912
14	3968
15	3470 X

• 8 ft length of rope—figure 8 knots on each end—factor 1.2 fall—over a carabiner.

New Joker 9.1 mm		“Cat Pee 9.1 mm”
# Falls Held	Max Load Seen	# Falls Held	Max Load Seen
6	4148	5	4045

Factor ~ 1.2 over a Omega Steel
Joker 9.1		Joker w/ Cat Pee
Drop	Max Force (lbf)	Drop	Max Force (lbf)
1	2189	1	2279
2	3007	2	3081
3	3465	3	3536
4	3763	4	3878
5	3979	5	4045
6	4148	6	3592 X
7	4029 X

• 4 ft length of rope—figure 8 knots on each end—factor 2 fall—direct onto anchor.

New Joker 9.1 mm		“Cat Pee 9.1 mm”
# Falls Held	Max Load Seen	# Falls Held	Max Load Seen
5	2759	3	2357

Factor ~ 2 w/ Figure 8 in Both Ends
Joker 9.1		Joker w/ Cat Pee
Drop	Max Force (lbf)	Drop	Max Force (lbf)
1	1248	1	1364
2	1891	2	2041
3	2260	3	2357
4	2488	4	No Drop X
5	2759
6	2316 X

• 8 ft length of rope—figure 8 knots on each end—factor 2 fall—direct onto anchor.

New Joker 9.1 mm		“Cat Pee 9.1 mm”
# Falls Held	Max Load Seen	# Falls Held	Max Load Seen
3	2583	2	2687

Joker 9.1		Joker w/ Cat Pee
Drop	Max Force (lbf)	Drop	Max Force (lbf)
1	1708	1	1754
2	2380	2	2470
3	2583	3	2687 X
4	No Drop X

Observations

• The "Cat Pee” rope was approximately 95% of the static strength of a new rope.
• You can see during the first drop tower test that the "Cat Pee” rope saw higher loads faster.  This means that it did not have equal elastic properties to the brand new rope. 
• The "Cat Pee” rope withheld slightly fewer falls in all other drop tower tests.
  

Further Information

I contacted Pit Schubert who is an expert in climbing gear accidents and testing and asked if he had done any tests regarding urine and ropes.  His response is below:

“I made test with ropes and human urine—I put rope samples in a pot with urine over night and sent them to the university of Stuttgart for testing according to EN 892—the result: reduction of the number of falls 30%—after this I had the idea, that a rope in a pot of urine over night is not realistic—so I put only a lot of urine drops on the rope samples, but morning urine (because morning urine is stronger than day urine)—the result: reduction of the number of falls 13%.

I hope this is helpful for you.

I published this in my book 'Sicherheit und Risiko in Fels und Eis', Volume 2, (only in German, translated in Spain, Czech, Netherlands and Japanese language, but not in English—sorry).

Kind regards,

Pit"

Conclusions

It would appear that urine on a rope DOES affect the ultimate strength and the number of falls held. The extent to which it affects the properties of a rope and how it would relate to real world climbing situations is variable, undetermined and ultimately unknown given the many factors specific to each situation (amount of urine, age of rope when exposed, how long exposed to urine, type of loading scenario, etc). It also appears that either the urine alone and/or the washing in baking soda affected the elastic properties of the rope, making it less dynamic and causing increased force on the anchor during the drop tests. Though the results seen here don’t necessarily show that urine on a rope can be catastrophic, it is always ultimately up to the climber him/herself to make the decision regarding the use of their own equipment, especially after peculiar and sometimes unknown circumstances.

A Final Word

Even if the testing here isn’t conclusive to show possible catastrophic circumstances if your rope is exposed to urine—don’t pee on your rope. It’s kinda gross.

Be safe,

KP

November 29, 2006—Gear from Ukraine

I received an email a while ago from a gentleman who had some old gear laying around. He said it was from Ukraine, most with no manufacturers markings, ratings, etc—it had been sitting around for quite a while and he was never about to use it so asked if I would be interested in breaking it—just to see how strong it was. I thought, why not?

The Gear

There were some cams from the Ukraine, unknown cams, a handful of stoppers and a few carabiners.

Tests

We tested the gear in the tensile testing machine using the same fixtures we would when testing comparable BD gear. Cams were tested at 50% retracted; biners were tested in Closed Gate; Stoppers were tested in standard wedge jig. We also compared the results to similar size of BD product for relative comparative purposes.

Results

Description	Rating (kg or kN)		Tested Strength (kN)	Failure Mode	BD Compare	Rating (kN)
Cam—Large Ukraine	1800 kg	17.65	15.72	Cable Midspan	#1 Camalot	14
Cam—Small Ukraine	1800 kg	17.65	13.70	Axle Shear	#.5 Camalot	12
Cam—Titan	15 kN	15	11.07	Runner	#.75 Camalot	14
			15.81	Runner
			17.84	Ball Swage Failure
Cam – Small Unknown	NA		13.59	Axle Bend / Cam Shear	.4 Camalot	10
Biner – D	2200 kg	21.57	28.76	Nose Hook Failure	Light D	24
Biner – D	2200 kg	21.57	28.76	Nose Hook Failure	Light D	24
Chock—Silver Taper	NA		11.02	Swage Pullout	#9 Stopper	10
Chock—Pink Taper	NA		7.40	Swage Pullout	#9 Stopper	10
Chock—Large Curved	NA		8.76	Cable at Nut	#11 Stopper	10
Chock—Medium Curved	NA		9.61	Cable at Nut	#10 Stopper	10
Chock—Small Yellow	NA		3.79	Cable at Nut	#5 Stopper	6
Chock—Small Purple	NA		4.32	Cable at Nut	#4 Stopper	6

Observations & Comments

Cams

• None of the cams met their rating. In two of the three cases, the failure mode was peculiar and undesirable (cable failure midspan, and axle shear).
• The Titan cam runner broke below rating, we tested with another piece of tied cord, it broke there again, then we tested without any webbing in the system and got the ball swage to fail at above the product rating.

These undesirable failure modes could be a result of age of the product, material selection, previous abuse, or a combination of all three.

Biners

The biners were burly strong—stronger than their rating, and exhibited typical failure modes for these types of biners.

Stoppers

• Stoppers usually fail “Cable at Nut”Two of the six failed by the cable pulling out of the swage—though one above a comparable sized BD stopper’s rating, and one significantly lower. This failure mode is probably the result of poor swaging.The medium and larger size stoppers were slightly weaker than a comparable size BD stopper.
• The smaller stoppers were significantly weaker that a comparable size BD stopper.

Bottom Line

Climbing is a serious game—buy your equipment from reputable manufacturers. Be careful of knock-offs and small-time garage-shop gear. I’m not saying that there can’t be good small-shop gear out there—but in most cases these companies don’t go through the certification processes and have the quality systems in place in order to ensure repeatable manufacturing processes and that the gear they are producing consistently meets its intended ratings.Thanks to Jim Thompson for sacrificing his old, unknown, questionable gear so we could maybe all learn something.Be safe in the hills,KP

 

November 9, 2006 – Connecting Two Slings Together

Hi there,

So sometimes I like looking into and investigating different climbing gear or situations because I’m curious, sometimes people ask me or email me a question, sometimes I see some sketchy stuff out at the cliffs and sometimes something happens out in the field that I end up hearing about and decide to spend some time looking into it to maybe answer some questions, or maybe even end up posing more.

Investigating joining two slings together and how strong they are is a combination of all of the above. I had kind of been wondering about all these skinny slings on the market; I had a student send in a comparison on different methods of joining slings together asking which way was the best; and there was an incident with John Sherman recently where he had a sling on his anchor break when he used two slings girth-hitched together—luckily no one was hurt. For details on John’s incident you’ll have to sift through info HERE.

Therefore, all of these things prompted me and my crack crew of QA Engineering guys to throw a quick list of experiments together and do some testing. Please note: This is NOT intended as a in-depth investigation into John's recent incident, rather just as information related to the joining of two slings together in general. So grab yourself a beverage of choice, because this one could get a bit long-winded.

INITIAL THOUGHTS

Personally if I have to join two slings together, I generally use the Strop Bend (close to a girth hitch, more later)—because it’s clean and symmetrical. When it comes to forces, loads, etc., we engineering-types like symmetry. Also, I just make sure the two strands are the same width—no one ever told me that, I just thought it made sense. Think about wrapping a piece of fishing line around your finger and pulling—ouch—the different diameters really cut into you. But one finger wrapped around another and pulling—no bigs. 

But I just did things that way because I did, and luckily I never really needed to test it out by accidentally taking monster whippers onto girthed together slings. I was hoping we’d learn some good info both for ourselves and to share with other climbers out there.

It’s worth noting that surfing around the web for a while will bring up all kinds of info on this topic— some accurate, some not-so-accurate. One interesting tidbit of good information we found was a blurb by my predecessor here at BD, Chris Harmston. 

It appears that he had already done some testing several years ago—but things have changed slightly since then—thinner and thinner webbing is now on the market. We would repeat some of his tests, and add some new ones to the mix.

So what did we do?

Well I have a spreadsheet about 20 tabs deep with all of the raw data, summary, statistical analysis, comparison, rankings, percentage differences, etc., etc.—as well as just as many more of photos pre testing, test set-ups, post testing, etc.  But I’m not sure if we have enough bandwidth to post all of this data, plus I doubt anyone would look at it; so let me do my best to summarize.

THE TESTS

Tests we performed included:

Tensile Strength (static)

Pulling slings connected to failure in a tensile test machine—measuring ultimate load

Tensile Strength (dynamic)

Using Black Diamond’s drop tower, drop a mass onto two connected slings

• Slings were girth hitched together for all tests
• Mass was 80 kg
• Fall factor was ~2
• Drops were repeated using the same rope per sling specimen, with loads increasing with each drop (because the elastic properties were being taken out of the rope)
• Loads on each drop, and number of drops recorded until sling failed
• New dynamic climbing rope (11 mm) per specimen

Cyclic

Using a pneumatic cylinder, we cycled connected slings to a load of ~3.5 kN (~800 lbf). Note: This is approximately the load we could generate when performing a gnarly bounce test as if aid climbing, or a bit more than a typical toprope anchor sees during ‘normal’ toprope belay situations.

Note: It’s worth noting that loads on toprope anchors can easily exceed this. For more, read Tyler Stableford’s excellent article in Rock & Ice Issue #133, June 2004, "Climb Safe: Taking it from the Top."

 

THE SAMPLES

Materials

Of course there are many many types of slings out there—we used the following materials:

• 11/16” nylon (think cam sling material)
• 12 mm Black Diamond Dynex
• New 10 mm Black Diamond Dynex

Note: Black Diamond currently sells 12 mm Dynex, but is coming out with 10 mm Dynex

Note: Several other manufacturers are currently selling 10 mm Spectra, 8 mm Spectra and even 6 mm Spectra slings. Some of these were tested as well.

Note: For our purposes, Dynex, Spectra, & Dyneema can be considered the same material

Methods of Connecting

We used three main knots to join the two slings:

• girth hitch
• strop bend
• climber’s hitch

Girth Hitch

Strop Bend

Climber’s Hitch

Note: The girth hitch and strop bend are VERY close. I believe that most people use the term "girth hitch" loosely and it in effect covers both the true Girth Hitch as well as the Strop Bend. In these experiments we will treat them differently.

Material Combinations

We tested many different connecting methods in combination with material combinations in order to try to shed some light on the subject:

Note: Photo only shows some of the combinations and materials tested.

RESULTS

To try to give all our results would take pages and pages, here is the as-short-as-I-could-make-it version:

Note: For ease of comparison, strength values and reductions are compared to 22 kN—which is the CE minimum requirement for a NEW sling—so these numbers aren’t actual reduction in strength of the slings, because it’s possible that they are stronger than 22 kN when new—follow?

Tensile Tests

Chart shows percentage of when new, sling strength (i.e. 22 kN):

	Girth Hitch	Strop Bend	Climber’s Hitch	Comments
11/16 Nylon & 11/16 Nylon	70%	80%	88%	Nylon failed
12mm Dynex & 12mm Dynex	70%	85%	Not tested
12mm Dynex & 11/16” Nylon	55%	55%	Not tested	Nylon failed
10mm Dynex & 10mm Dynex	53%	58%	57%	Dynex failed
10mm Dynex to 11/16” Nylon	54%	54%	54%	Nylon failed
11/16” Nylon to 10mm Dynex	46%	54% (symmetry)	54% (symmetry)	Nylon failed
8mm Dynex & 8mm Dynex	57%	53%	56%	Spectra failed
8mm Dynex to 11/16” Nylon	56%	57% (symmetry)	53%	Nylon failed
11/16” Nylon to 8mm Dynex	43%	57%	53% (symmetry)	Nylon Failed

Note: the Strop Bend and Climber’s Hitch are symmetrical, and therefore the results for using 10 mm Strop Bend to 11/16” Nylon is the same as using 11/16” Nylon Strop Bend to 10 mm, etc.

10 mm Dynex Girth Hitched to 11/16" Nylon—Static Tensile Test

10 mm Dynex Strop Bend to 10 mm Dynex—Static Tensile Test

8 mm Dynex Climber’s Hitch to 11/16" Nylon—Static Tensile Test

Observations

• Joining two slings reduces the ultimate strength—and in some cases by up to and over 50%
• When nylon and a Dynex or Spectra material were combined, the nylon failed in all configurations
• In general terms, the narrower the material used, the greater the reduction in strength
• Also in general terms, mixing widths of materials when joining slings results in a greater reduction of strength

Drop Tests

(all samples joined using a Girth Hitch)

	Number of Drops	Ultimate Failure Load	Comments
11/16 Nylon & 11/16 Nylon	14	~14 kN	Nylon broke
12mm Dynex & 12mm Dynex	>10	~14 kN	Broke 2 ropes
12mm Dynex & 11/16 Nylon	>10 >7	~13 kN ~12 kN	Broke 2 ropes Broke 2 ropes
10mm Dynex & 10mm Dynex	5 4	~11 kN ~11 kN	10 mm Dynex broke 10 mm Dynex broke
10mm Dynex & 11/16 Nylon	4 3	~12 kN ~11 kN	10 mm Dynex broke 10 mm Dynex broke
8mm Dynex & 8mm Dynex	2 3	~10 kN ~11 kN	8 mm Dynex broke 8 mm Dynex broke
8mm Dynex & 11/16 Nylon	2 5 3	~9.5 kN ~11 kN ~11 kN	Nylon broke 8 mm broke 8 mm broke
6mm Dyneema & 6mm Dyneema	2 2	~9 kN ~9 kN	6 mm broke 6 mm broke
6mm Dyneema & 11/16 Nylon	3 2	~11 kN ~9 kN	6 mm broke 6 mm broke

 

8 mm Dynex STROP bend to 11/16" nylon—drop test— before failure

10 mm Dynex Girth Hitched to 11/16” nylon—drop test

8 mm Dynex Girth Hitched to 8 mm Dynex—drop test

Observations

• When webbing sizes are mixed, and under dynamic loading situations, the narrower strand typically fails (in all but one of our tests)
• During one test a girth hitch slipped to a strop bend—this sample ultimately went many drops more than as if it had been girth hitched 
• More testing required to verify if a strop bend performs significantly better than a girth hitch in dynamic loading situations—we tested two more samples with intentional strop bends

	Number of Drops	Ultimate Failure Load	Comments
10 mm Dynex (STROP BEND)	6	~13 kN	Nylon broke
11/16 Dynex (STROP BEND)	6	~12 kN	Nylon broke

• It appears that the slings joined with the strop bend performed significantly better in dynamic loading scenarios than slings joined with a girth hitch (compare to data above) held approx 50-75% more drops, as well changed the failure mode to the nylon sling
• In all tests performed, it took more than one relatively severe drop to induce failure into the system

Cyclic Tests

All configurations and samples tested (11/16” nylon to 11/16” nylon, 10 mm Dynex to 11/16” nylon, 8 mm Spectra to 11/16” nylon) using Girth Hitch, Strop Bend and Climber’s Hitch all surpassed 5000 cycles at a repeated cyclic load of 800 lbf.

Comments

• Repeating these tests with a combination of an increased load and/or varying the rate of load may differentiate between stronger vs. weaker joining methods and materials combinations for repeated cyclic scenarios

CONCLUSIONS & FINAL THOUGHTS

As always, I must state a disclaimer that these findings are somewhat unofficial—just some information to think about. I’m not a climbing guide and don’t even play one on TV. These experiments are NOT all inclusive or totally encompassing by any means—much more testing would be required in order to come to any firm conclusions. It is important that all climbers use their best judgment out in the hills.

First off, our results were very comparable to Chris Harmston’s findings, and I agree with his recommendations—before you join two slings together think about the following:

• Is it possible to use a longer sling altogether?
• If you need to join to slings, using a carabiner is stronger

And in addition:

• If you must join two slings, use the same materials and width
• Symmetrical knots (like the Strop Bend and Climber’s Hitch) appear to perform better than a standard Girth Hitch when joining two slings together

General

• It’s interesting to note that when webbing sizes are mixed and tested in slow static pulls, the nylon failed, however under drop tower dynamic situations, the thin webbing failed. That just verifies that the rate at which loads are imposed on a system can make a difference in ultimate failure load and mode.

So why did John Sherman’s thin sling cut when loaded in the way it was?

• Looking at the photo of the anchor set-up, I question how ‘equalized’ this anchor was.  It appears to me that the anchor point in question took the majority of the load in this situation, however, the loads seen in his toprope, rappelling scenario should still have been well within the limits of the material used.

John Sherman comments: "The anchor photo was shot the next day after I had re-rigged the anchor to finish my work the day before (the only re-rigging was to use the static line instead of the broken sling), then re-rigged it back to the previous (or close to) for the photo. I don't disagree that the failure side might have taken more weight (though I tried to avoid this), but the photo could be misleading as the clove hitch could be an inch or two off. Also when weighted the rope took a slightly different angle (the slings lift a few inches when the system straightens)."

• It’s interesting that his narrow web cut. As stated above, in all of our experiments, the only time that the narrow web cut was during the drop tests. This leads me to believe that perhaps his loading scenario was much more dynamic than originally suspected; or perhaps his girth hitch was not "dressed" (i.e. web folding over itself causing increased stresses).

"The girth hitch had a half twist in it—did this increase tension? Also the knot shows a distinct V-groove in the middle of the dyneema—it looks like there was extra tension along the center of the webbing making it act as if it were a smaller width. The knot pinched one length of dyneema against the other as the two strands exited the knot. One stand failed, the other was damaged as well at the same spot in the knot."

• It’s also worth noting that the cut of his narrow sling appears to be very clean—on all of the tests we performed, there was much fraying, etc of the ends after the breakage. Also, all of our narrow web failures went diagonally across the web, whereas John’s appears to be very perpendicular to the web.  Could it be possible that there was already a slight ‘nick’ in his thin web which allowed the break propagation during loading?

John Sherman’s clean cut thin web

Typical frayed ends of webbing after breakage

• So what is the exact reason, according to the laws of physics why John’s sling cut the way it did? I don’t know—but maybe someone has it out for him?? (Watch your back John.)

"BTW There's more than a few people who have it out for me—however only two climbers have ever been to the cliff where this happened and we were both on rappel at the time the sling broke. And any saboteur would have to be helluv clever to cut the dyneema then also nick the spectra on the backside of the knot. And why not just slice my rope? Furthermore my dog was chillin' atop the cliff and would have probably barked if a poacher or other person approached. (My dog is 12 and her teeth are worn down so she's not a suspect.)"

Hopefully his incident as well as the experiments and results described above will at least get you thinking a little bit the next time you need to join two slings together.

Climb safe out there,

KP