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