Absurdly good gear since 1983

Webbing Info


Basic Strengths from the manufacturers catalog:

 Type Common Name Used by us as  Breaking Strength Lbs
 1/2" tubular nylon  tie off  grab loops 1000
 9/16" tubular nylon  super tie off  super tie off  1500
 9/16" tubal nylon  super tape  hook slings  2400
 3/4" tubular nylon  3/4" tube not used 2300
 11/16" tubular nylon 11/16" tube slings, daisys 3900
 1" tubular nylon  1" tube aider steps, slings  4000
 2" tubular nylon 70's swami belts not used 7000
 3" tubular nylon 3" tube, light leg loops 3200
 3/4" flat nylon 3/4" flat, heavy aiders, some daisys 2600
 1" flat nylon 1" flat, heavy aiders, haul straps 3700
 3/4" flat nylon 3/4" flat, thin grab loop, trim 900
 1" flat nylon 1" flat, thin ledge susp, trim 1300
 2" flat nylon 2" flat medium shoulder straps etc 4500
2" flat nylon 2" seatbelt haul straps, harness 6500
 1" type II nylon seam tape trim, rumpsak 600

Standard nylon slings made of 11/16" webbing are rated to 4900 lbs approx.
Note: kn = 224.8 lbs +/-

Subject: water-knot slip failures

From: Tom Moyer <tmoyer@xxxxxxxxxxx>
Newsgroups: rec.climbing
Date: Wed, 24 Mar 1999 12:59:14 -0700

Hey all -

here's a report I just got around to writing on some water-knot testing
I did a while ago. This testing was very interesting and takes care of a
lot of concerns I had about strange and unconfirmable failures of this
knot. I posted it to the MRA and SAR lists - thought others might want
to have a look, too.

- Tom Moyer

Anecdotal evidence exists to suggest that water knots - commonly used to
join webbing into a sling - sometimes fail by slipping. I have found
through testing on a load frame that this knot gradually slips when
cycled repeatedly with loads as low as body weight. When the tails have
slipped all the way into the knot, it fails. This resolves the concern I
have had about "mysterious" failures of this knot. I believe it is
completely safe to use as long as it is checked and found to have
sufficient tails before loading.

I have been told many anecdotal stories of accidents caused by the
failure of water knots (aka ring bends or overhand follow-through knots)
by slipping. Understanding these failures is of some concern to mountain
rescuers who use this as a standard knot for tying two ends of a webbing
sling together. Many climbing and rescue texts recommend leaving plenty
of tail with this knot and pretensioning it carefully to avoid possible
slipping, but none of them provides any detail on failures. Past
pull-testing I have done on water knots (with sufficient tails) showed
no slipping failures - no matter how poorly the knot was dressed or how
poorly it was pretensioned. This caused me some consternation. If a knot
occasionally has mysterious failures that I can't duplicate, should we
be using that knot for rescue work? Suggestions by other climbers (and
the temporary availability of a programmable load frame) prompted me to
look at the possibility that these knots were slipping over time under
repeated loading and unloading cycles, rather than by slipping when
loaded for the first time.

Test Methods
I used a small MTS load frame to pull on a loop of 9/16" tubular webbing
tied with a water knot. The load was cycled from 0 to 250 lbs at a
fairly slow loading and unloading rate (about two seconds per cycle).
Loads and extensions were measured directly by the load frame. The test
was halted automatically upon failure of the knot.

The test showed consistent slipping of one of the tails into the knot at
an average rate of 0.0035 inches per cycle. A knot that started with
tails almost three inches long failed in 806 cycles. It was interesting
to note that only one of the tails slipped into the knot - the one on
the "top" side of the knot.

A second test with overhand safeties on the water knot gradually slipped
through 1.75 inches of tail at about the same slip rate (0.0028 inches
per cycle), and then cinched and did not slip any further.

A loop tied with a water knot was loaded with a static pull of 200 lbs
to check whether the knot was slipping by creeping. The test was run for
thirteen minutes. During the first eight minutes, the loop elongated by
0.025 inches. After that, it had no significant elongation. The water
knot seems to be affected by loading and unloading, not by a static

A third cycle test was done on a loop tied with a single fisherman's
knot. Over the first 750 cycles, the loop elongated by 0.247 inches.
After that, no further elongation occurred. The test was discontinued at
1630 cycles.

Water knots definitely fail by slipping under cyclic loading. Low loads,
such as body weight, are sufficient to cause failure. Other knots (such
as a single fisherman's) tied in the same material do not exhibit this
kind of failure. Overhand safeties tied on top of a water knot may
prevent the failure, but do not guarantee it.

This is not all bad news for water knots. I now understand the mechanism
of failure and know how to prevent it. This is a lot more comforting
than using a knot about which I have suspicions. I will always check the
length of the tails on every water knot - and particularly every fixed
rappel anchor tied with a water knot - before trusting my life to it. We
will continue to use water knots in Salt Lake County SAR, and continue
to require long tails on this knot as we always have.

Subject: test report, knots in spectra and nylon
From: matt.dimeo@xxxxxxxxxxxx
Newsgroups: rec.climbing
Date: Thu, 08 Jul 1999 20:17:56 GMT

Chris Harmston at Black Diamond showed his typical generosity and
pull-tested some samples for me, so I'm passing on the results
to add to the general knowledge base.

First some background: some months back there was a rec.climbing
discussion about Webolettes and their application. At the time,
I brought up the possibility of making your own out of spectra
cord with loops tied in the ends. This test was meant to check
the feasibility of that.

I figured that if I could tie a spectra-cord "webolette" with strength
comparable to a 7mm nylon cordelette, I'd do so, preferring cord
to webbing for self-rescue reasons.

As it turns out (see results below), it's not even close. Nylon
cord is stronger than I had remembered, for one thing, and having
a single strand of cord cuts the strength nearly in half over a loop.
I actually figured that out before I sent the samples off, but after
I had already bought and cut the cord. This probably would have
been obvious to many of you.

I sent three samples each of the following configurations, and
got these results:

Configuration #1: spectra cord loop, tied with triple fisherman's
(i.e. a normal cordellete)
Samples all broke @pin, at 3717, 3467, and 4034 lbf.

Configuration #2: 7mm Nylon cord loop tied with double fisherman's
Samples all broke @pin, at 3286, 3605, and 3299 lbf.

Configuration #3: spectra cord with figure eights tied at each end.
Backup knots were used, but made no difference (they didn't come
tight). This is the webolette configuration.
Samples all broke @knot, at 1779, 1793, 1884 lbf.

Configuration #4: As #3, but with a triple-fisherman loop in each
end (see below).
Broke at knot, at 1745, 1725, 1709 lbf.

The knot tied in #4 was created by feeding a triple fisherman knot
through itself. To tie it, start tying a 3-fish around a pencil,
then feed the short end back through along the pencil, pull out
the pencil, and tie the other half of the 3-fish. You end up with
a small loop.

Conclusions and observations:
1. nylon cordelletes didn't break much weaker than spectra, so if
you use spectra cordelletes because you think they're stronger, you
might be wasting your money.
2. The triple fisherman loop I sort-of invented didn't break any
stronger than the figure eights. Actually a little weaker.

all cord used was new. The spectra was 5.5mm blue water. The
nylon was 7mm, don't know the manufacturor. The test rig used 10mm
pins at 4"/minute.

Send email if you have any questions about the above.

Claimer and Disclaimer:
Any mistakes above are mine, not Chris's, and not Black Diamond's.
If you make safety decisions based on any of the above data, and
your head pops off as a result, it's your own damn fault.

Subject: Biner Orientation for Sport Draws
From: Chris Harmston <chrish@xxxxxxxxxxxxx>
Newsgroups: rec.climbing
Date: Tue, 4 May 1999 09:45:53 -0600

I have to dissagree with the recommendations of having the gates face the
same way or the opposite way, every situation is different and may
require different techniques. I recommend setting up draws with a
selection of different length of runners with the biners oriented in the
same direction and the opposite direction. I only recommend fixing the
bottom biner. Here are my reasons in order of importance (based on
likelyhood of failure in my opinion):

Note, I think through these issues EVERY TIME I clip a piece of pro on
every route. Learn to do this quickly. Assess every piece of pro every
time. I do not believe that there is one technique that works in every

1) Bottom biner must not be loaded over an edge or buldge. Use different
length of draw if needed. If this is not possible then use a locking
biner. Look for rotational effects. The buldge or edge may not be
located directly below the bolt but could be off to the side. Make sure
you think about how the draw will move when you fall from different places
on the route above you. Often times a route will force you to climb both
to the right and to the left of the piece below you. Remember this when
clipping your pro. Try to assess where you might be most likely to fall
from and set up your pro accordingly.
2) Top biner must not be loaded over an edge or buldge. On bolted sport
routes this does occur fairly often. Use a locking biner for these
situations, two biners, add a backup tie off, or better yet if you think
you might fall on this bolt-BAIL. Then slap the first ascentionist
repeatedly until they fix their fuckup. Often times you can simply rotate
the biner with the gate opening downwards to reduce the likelyhood of the
buldge opening the gate. In general I try to make sure that the gate
faces away from the bolt head. It can interfere with the biner gate in
some rare situations. Top biners are much less likely to unclip if they
are not fixed to the quickdraw, therefore I do not fix the top biner to
the draw.
3) Bottom biner must not be back clipped. Unclip and reclip the rope
until it is clipped correctly.
4) Bottom biner gate must face away from the direction you are climbing
5) Orientation of either biner is independent of where you are clipping
from. They are dependent on where you are going and the variables above.
Be able to clip with either hand with the biners facing either direction.
Setting up your draws and clipping them in one direction just because you
have poor technique is a bad excuse that could have harsh consequences
given the right circumstances. Learn the pinch clip and the index clip
and the palm clip and and and. Be proficient at any clip! There are times
when this is not feasible. When climbing at your limit you may need to
force a certain type of direction to make the clip easier. Be aware that
this may not be the best situation when falling from above.
6) Carry 1 or two draws with locking biners on both ends for those
situations where you can't avoid biner interaction with buldges or edges
or when faced with a hard crux or runout where gear failure would be

These are my personal opinions from my own experiences in climbing not
from testing that I have done.

Chris Harmston (chrishxxxxxxxxxxxxxx).
Quality Assurance Manager. Materials Engineer BS, ME.
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552

Webbing Loop Strength Q:
From: Chris Harmston <chrish@xxxxxxxxxxxxx>
Newsgroups: rec.climbing
Subject: Re: Another webbing strength question
Date: Mon, 26 Jul 1999 09:47:48 -0600

On Sun, 25 Jul 1999, Bob Austin wrote:
>Question. I have a piece of 9/16" tubular webbing that is rated at 12kn. I
>tie an overhand knot in it at one end. How strong is the loop that I've
>just created? At what approximate point would it fail?

Good question. I had never tried this before. I went to the lab and
performed this test. I used two runners, one with a overhand knot in the
center and one in the normal configuration. These were 11 inches long and
were 5/8" spectra. Both were new. I did not test nylon runners.

Loop Rating: 22 kN = 4946 lbf.

Loop strength: 26.6 kN = 5974 lbf.
Loop with overhand in center: 15 kN = 3367 lbf.

Nearly a 50% reduction in strength.

So, to answer Bob's question I would say that his runner would break
somewhere around 7 kN. Now, this is assuming that he was asking the
question about runners, not single strand webbing. To answer the question
on single strand with a knot in one end he would have to be explicit
about the test setup. Chris

Chris Harmston (chrish@xxxxxxxxxxxxxxx).
Quality Assurance Manager. Materials Engineer BS, ME.
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552

DISCLAIMER: Unless otherwise indicated, this correspondence is personal
opinion and NOT an official statement of Black Diamond Equipment Ltd.

Subject: Re: reslinging cams
From: John Byrnes <byrnes@xxxxxxxxxxxxxxxxxxxx>
Newsgroups: rec.climbing
Date: Tue, 12 Jan 1999 14:48:33 -0700

Karl Lew wrote:
> OK, so I'm stupid. I just realized that I've been using quickdraws to
> extend my cam slings. DOH!

Yup. I see this all the time.

> I'm gonna buy some 12" Blue Water sewn open
> runners and girth hitch them to my cam slings.

There's a better way.
All my cams are set up with 5.5mm spectra/kevlar/whatever to form
an 8 to 10" loop. Position the knot (double or triple fishermans)
about 3/4ths of the way from the cam. Put a thin piece of tape
about 1/2" from the stem to short-circuit the loop and form an "8"
with a big loop and a small loop. Leave just enough room to be
able to clip a biner between the tape and the stem in case you
want to use it as a quickdraw in a pinch. The tape keeps the loop
from shifting, the knot out of the way, and keeps things hanging
neatly on the rack. Eventually, the cord will take a "set" which
you'll find beneficial.

Color-code the cord to match the color of the Mfg's sling.
This way, you'll still have a "Yellow Camalot" for your less
retentive partners. Use soft cord.

I've found that the smaller the cam, the longer the sling should
be (at least for free climbing) because the smaller springs allow
the cam to walk more easily. Smaller persons may find having cams
bashing them in the knees to be a problem. Ignore their whining.

Now you can place a cam without having to put a draw on it. You
can carry fewer draws. Your rack will be lighter. You can place,
clip and be moving sooner. You might start to consider dumping
all those wired stoppers and replacing them with roped stoppers...

- Lord Slime, those slings they come with are worthless.

Subject: Re: reslinging cams
From: "Karl Lew" <karl_lew@xxxxxxxxxxxx>
Newsgroups: rec.climbing
Date: Wed, 13 Jan 1999 11:51:55 -0800

>Chris from Black Diamond posted some data a while back suggesting that
>spectra slings girth hitched together are much weaker than a biner

Thanks for the warning. I found the post (see below). Looks like
girth-hitched spectra runners fail at 14kN or less. That's something to
watch out for.
(FISH Note: 14kn = 3147 lbs. What are we watching out for again?)

From: Chris Harmston <chrish@blkdiamd.com>
Date: 1995/03/21
Newsgroups: rec.climbing

Just for your information.
I just tested two sets of SEWN samples in our test lab.

Sample 1: 2- 5/8" Spectra Runners Girth hitched: Failed at 3678 lbs,
at the Girth Hitch knot. This is 1492 lbs below our 3 Sigma rating of 5170

Sample 2: 2- 9/16" Nylon Runners Girth hitched: Failed at 3191 lbs, at
the Girth Hitch knot. This is 630 lbs below our 3 Sigma rating of 3821

Note: these runners are new and do not reflect the strengths of runners
which have been in use (they will be weaker!). One sample is not
statistically valid. You can expect that many samples would fail below
this load I measured if we were to test many samples.

Warning: This test is not an indication that girth hitching your runners
is "safe". Girth hitching is not recommended by Black Diamond. If you
use this technique to extend your runner length then you are responsible
for it. Girth hitching is weaker than using biners to connect the runners.

Chris (Quality Assurance Manager)

Chris Harmston (chrish@xxxxxxxxxxxcom)
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552

Re: Cordelette prefs? 
Author: Clyde Soles
Email:   csoles@xxxxxxxxxxx
Date: 1997/01/16
Forums: rec.climbing

tdonalek <tdonalek@nospam.com> wrote: "rabbit runners"? "four strands"? explain please!

Showing my age. A rabbit runner was an old Forrest product that was
simply a sling with biner loops at both ends. Before Spectra webbing
came along, they didn't instill much confidence. For an anchor, clip one
loop to each outside piece, bring the middle up to the center piece
(there are now four strands), tie an overhand. I'm sure Chris "ASCII
artist" Weaver can illustrate this for you.

Re: re-slinging Lowe Tri-Cams 
Author: Clyde Soles
Email:   csoles@xxxxxxxxxxxx
Date: 1998/04/25
Forums: rec.climbing

Rawdomg <rawdomg@xxxxxxxxxx> wrote:
> I got a slick tip about a year ago that has worked well for me. Drive the
> steel roll pin 3/4 of the way out with a drift pin or flat-tip punch, then
> slide in a spectra quick draw. Press the pin back in and voila. I use Blue
> Water 6 inch draws which have a rated strength of 3000 kg, way above the
> original 3/8 in flat nylon loop.

Um, bad tip. Lowe was especially concerned about that procedure because
of high potential for stress fracturing the fairly thin aluminum. When I
tested some old tricams, that's where they all broke...not the ratty
looking sling.

Re: Rigging my new Hexes 
Author: Clyde Soles
Email:   csoles@xxxxxxxxxxxxxxxx
Date: 1998/04/15
Forums: rec.climbing

Kenneth Cline <cline+@xxxxxxxxxxxxxx> wrote:
> A double fisherman's knot in spectra is certainly
> stronger than using 5mm nylon (why do people still call it perlon?)
> for slinging hexes, and your suggestion to the contrary is ludicrous.

Yep, this is all rather pedantic. But since you asked, it goes back to
WWII (I don't have my reference materials handy so I've probably got
this wrong). Dupont invented a synthetic polyamide type 6 molecule chain
called Nylon that changed the world. The Germans(?) later developed a
type 6,6 molecule chain (Perlon) which produced a fiber with higher
tensile strength.

> And yes... There are good alternatives. Gemini works well for
> slinging hexes, but too stiff for cordalettes. Vectran is knottable
> and good for all-around use. I am considering switching to Vectran
> for my cordalette when I retire the Spectra.

I like Web-o-lettes from Mountain Gear (a long rabbit runner) since they
aren't as bulky.
Clyde Soles

Re: Slinging Camalot Jr.s
Author: Chris Harmston
Email:   chrish@xxxxxxxxxxxxx
Date: 1995/06/06
Forums: rec.climbing

On 4 Jun 1995, Neal Weiss wrote:
> I've given qll my Camalot Jr's (4) and several old unslung Aliens an after
> market sling job at Ragged Mountain in New Hampshire. Don't know how BD
> is slinging the Jr's, but Ragged Mountain did a great, straightforward
> job; 4" or 6" nylon slings (choice of color)for about $3 each. Spectra
> slightly more. All professionally and competantly bar tacked.
> Neal Weiss
> weiss@xxxxxxxxxxxx

Slinging Camalot Jr's requires that the webbing be doubled where it
contacts the plastic thumb bar. The inner webbing is not structural but
protects the outer from the cable. A simple loop sling is not adequate
and will fail at loads well below the 12 kN rating.

Chris Harmston (chrish@xxxxxxxxxxxxxx)
Quality Assurance Manager/Materials Engineer
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552

Re: Reslinging cams 
Author: Chris Harmston
Email:   chrish@xxxxxxxxxxxxxx
Date: 1995/11/13
Forums: rec.climbing

On 12 Nov 1995, Steven W. Tregay wrote:
> For old style camalots you can cut about 1/4" off each side of the black plasic
> and then fit a camalot Jr thumb piece and then sling. This only works on 1 and
> 2's. This was in a quick clip in climbing some time this past spring.

This may have been in quick clips, but this is not recommended by Black
Diamond in any way. The following is a letter I sent to Climbing magazine
following another letter to them regarding slinging Camalots.

April 21 1995

In reference to the Quick Clips (#151) by John MacDonald regarding the
retrofitting of double stem Camalots with Camalot Jr. thumb loops and
slings I am writing to state that this practice is not endorsed by Black
Diamond Equipment. We feel that this situation described and depicted in
Quick Clips is potentially dangerous.

1) Cutting the Nylatron Thumb Bar down to make room for the Jr. Thumb
Loop may create two potential problems. First, if in cutting the
Nylatron Thumb Bar you are to damage the cable in any way, this could
affect the strength of the Cam. Second, the Thumb Bar and trigger
assembly are designed to each other. Cutting the Thumb Bar short may
cause the trigger to bottom out on the Thumb Bar and not enable full
retraction of the cams.

2) Sewing slings on the Jr. Thumb Loop requires overlapped webbing. A
single layer of webbing as depicted in the diagram is insufficient. When
testing these situations we have found that the Thumb Loop will break
near 1000 lbs. After that the webbing is in contact with the cable. For
the single webbing situation the webbing is cut by the cable at loads
between 1500 and 2000 lbs. These forces are relatively easy to achieve
in normal climbing situations. Therefore, it will be possible to see
sling failure and possible injury from this situation. Black Diamond now
sews its Camalot Jr's. with runners that have a double layer of webbing
around the cable and Thumb Bar. The Thumb Bar still breaks at about 1000
lbs, but the runners do not break until near 3000 lbs. In fact, about
half of the batch test samples fail at the cable and the other half fails
at the runner. We do not recommend that you put runners on old style
double stem Camalots. If you need a runner on you Camalot Jr. then send
them to Black Diamond for a retrofit.

3) A doubled or girth hitched sling on either Camalot is also not
recommended by Black Diamond. The reason for this is that the runner
still has no protection from the cable. For the Camalot Jr. sling the
inner webbing is not structural, it is there to protect the outer webbing
which is the structural component. The sling is sewn in such a manner to
prevent the structural outside webbing from ever contacting the cable.
The inner webbing is sewn to the outer and this keeps them both in place
(i.e., the inner against the cable and the outer away from it).

Chris Harmston (chrish@xxxxxxxxxxxxxxxx)
Quality Assurance Manager
Materials Engineer BS, ME
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124
phone: 801-278-5552

Re: New slings for Camalots? 
Author: Chris Harmston
Email:   chrish@xxxxxxxxxxxx
Date: 1998/01/08
Forums: rec.climbing

See below for some more information you all may find enlightening.

On 7 Jan 1998, Stefan Axelsson wrote:
> In article <01bd1ae5$2f449a60$7d260ea7@cweaver>,
> Chris Weaver <cweaver@xxxxxxxxxxx> wrote:
> >While I admit that I didn't know BD's official opinion was this, it doesn't
> >address the point I was making. The point is that the tied sling is fine -
> >it's strong ENOUGH. The fact that it fails below the 12 kN rating proves
> >little. Your other gear will break long before the sling does.

I don't think tied slings are fine in all situations. They break well
below that of sewn slings, are prone to untying themselves, and I know of
accidents involving them (untying and cutting on Camalot cables). In
nearly every situation you will not generate enough force to cut or break
webbing or hardware. If you have a high fall factor with nearly static
belay (i.e. aid soloing is the most dangerous form of climbing in my
opinion because the forces are higher--if you use static belays) you
dramatically increase the possibility of failure.

> No they're not. The reason that you haven't heard about the cam
> cutting webbing in the way that you describe I would attribute to:
> 1) Not that many tie webbing like you describe,
> 2) Not that many take high factor falls.

I agree with these comments. The number one issue is that most people do
not hear the details of accidents. I have investigated quite a few gear
failure incidents. Gear does break during normal situations encountered
in climbing.

> Now, 12kN isn't that much to begin with in the first place, if you
> double that, not exactly true due to friction but we have to start
> somewhere, you land at about a factor one fall. Catch that with one of
> the more static belay devices on the market and the little red warning
> lights are sure to go off.

> >Black Diamond uses the 3-Sigma system to determine necessary breaking
> >strengths, and these strengths are far, far above what is necessary
> >in the field.

Absolutely incorrect. Just because we give a rating does not in any way
mean the product will not break. It is possible to break every piece of
equipment we make if the conditions are just right. Our rating system is
just that, a rating of where the gear fails when new and when tested in
the lab. We make products that will not hold falls. Climbers use these
to protect themselves routinely. So why do we do this? If we were to use
the strict engineering safaty factor rating and guarantee that you would
never break gear in any situation encountered in climbing then you would
not be climbing. Camalot Jr's would be for 8 inch cracks and would weigh
10 pounds. There would not be any Stoppers or Steel nuts. Carabiners
would be three times heavier and all would have autolocking sleeves.
And, you would all retire your ropes and gear after even the smallest
fall. So why do we sell gear we know has the potential to fail? Because
we are climbers and we recognize the need for the protection we sell.
Technique is what protects you foremost, not the gear. Placing protection
often to reduce the fall factor, equalizing small nuts, using low impact
ropes (carefull with these since they may stretch you into a ledge), etc.

> Whether BD use 3-sigma or slaughter a chicken at full moon to decide
> *breaking* strengths of their gear is of course totally irrelevant to
> the discussion of whether the chosen strength is sufficient or not.

The chosen strength of "12 kN" is not enough. You can generate more force
than this. It does not happen very often though. 12 kN is the force
chosen by the UIAA and CEN to be the limit of force in the rope during the
first drop of a factor 1.8 fall (and just happens to be the 3 sigma
strength of our Cam Jr's). This is not the force felt by the edge
they drop the weight over. REI has conducted drop tests and measured the
forces at the climber, belayer, and protection. They found that the force
on the protection is about 2/3 greater than that in the rope. This means
that the protection can see forces approaching 20 kN. Use an old fat rope
and you could generate even more force than this.

> As anyone with a background in mech. eng. can tell you, if you started
> rating other gear used in safety critical applications with the
> max. expected breaking load, instead of the more common 3 times safety
> margin to the yield stress of the material, you'd be out of a job. So,
> no, they are *not* "far, far above what is necessary in the field."
> Quite the opposite actually. Ask anyone involved in rescue work.

Correct. Climbing gear is not engineered to never fail. It is not
possible given the currently available materials and designs and costs.
Technique is what protects you foremost. Blind faith in anything is not
sound advice.

> That BD does not unnecessarily and purposely wish to introduce a weak
> point in their design by recommending that you tie a sling the way you
> have advocated in my mind reflects very favorably on them. Especially
> since the design impact is neglible in terms of cost, weight etc.

Single loops cut on the wire of the Jr's. These loads range from 1500 to
2500 lbs. With the doubled loop the cable breaks at loads over 3000 lbs
(rating is 12 kN = 2698 lbf.). We feel that the use of single
loops is not sound advice. They are still strong enough for the vast
majority of situations you could encounter. End BD recommendations.

The following recommendation is my personal one and is not to be taken as
recommendations by Black Diamond. I use single loops. I recognize the
limitations of doing this. I know that these can fail at much lower
loads. I never use these as the only piece of pro when there is the
potential for a high fall factor. I use double loops so that the webbing
can be extended. I also cover the wire with a 1/4" thick layer of
fiberglass tape and athletic tape to help protect the web from the cable.
Using tied slings is fine for many situations. I don't use them if I have
a choice.

Irrelevant FYI.
I have been climbing since 1981. I have onsighted 12- trad and 12+ sport.
I lead WI6 and have put up about 2 dozen first ascents on rock and ice. I
have no wall experience other than long free routes done in a day. Not
that this is pertinent to the discussion, but I am a climber. Safety of
gear is my hobby. Testing climbing gear is my job. I have BS degrees in
Physics and Materials Engineering. I have a masters degree in Materials
Engineering and quit my PhD program with 18 months to go so that I could
work for BD. I have been with BD for 5 years.

Re: Spectra slings and WD40 
Author: Chris Harmston
Email:   chrish@xxxxxxxxxxxxxx
Date: 1998/03/17
Forums: rec.climbing

On 17 Mar 1998, James Neal Singletary wrote:
> Steve Gray wrote:
> >> Help ! Anybody with any real technical knowledge about this....
> >> I got WD40 on a spectra sling while doing some repair work to me house
> >> yesterday.
> >> (Yes, I know, I shouldn't have been using climbing gear...)
> >> Do these things mix safely, or should I "sling the sling" ? Please
> >> respond quick - I'm off to Borrowdale tomorrow if the forecast's right.
> >> Steve Gray

> Spiral Climbing Company <DELETEclimb@xxxxxxxxxxxt> writes:

>James Neal Singletary wrote
> ``PETROLIUM BASED PRODUCTS'' are really that bad? Why are the washers on
> car oil pan drain bolts made out of nylon? How do plastic gas tanks work?
> Why is the spray nozzle on WD-40 cans made of plastic?
> FWIW, the ``Textile World Manmade Fiber Chart'' (Ciba-Geigy, 1990) on our
> office wall lists nylon 6 and nylon 6,6 fibers as being ``Generally
> insoluble in organic solvents'' and ``generally insoluble in most organic
> solvents'', respectively, and says of Spectra 900 and 1000, ``Some
> hydrocarbons cause swelling, especially at elevated temperatures.''
> Maybe you should write Allied Signal at their website and ask them about
> what might happen. Sorry this isn't a very timely response.
> With regards,
> James Singletary

Chris Harmston wrote:
The following test data was gathered in 1994. These results are not for
Spectra or WD40 but are relevant to the discussion.

BD made 16 11/16" nylon runners. 8 were stored in the lab and 8 were
soaked overnight in the lubricant T9 (which we use to lubricate camalots)
and then they sat in full sun for two days. Both batches failed at the
same value. The conclusion was that T9 does not affect the strength of
the runners.

I also conducted a series of tests on Nylon runners with WD40. This was
undocumented since it was my own gear. Again, these were still full
strength. I don't remember the data off hand since I did this 4 years
ago. I don't think that WD40 affects Spectra (our runners are half
Spectra and half Nylon). However, I have not tested this out and verified
it conclusively.

Chris Harmston (chrish@xxxxxxxxxxxxxx).
Quality Assurance Manager. Materials Engineer BS, ME.
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552

Physics of Screamers by YATES
Author: John Yates/ Pro Design USA
Email:   prodesig@xxxxxxxxxxxxxxxxxx
Date: 1998/12/08
Forums: rec.climbing

Hello all,

I friend of mine rang me up this morning and told me about a discussion
going on in this news group about forces involved with screamers and air
voyagers <<snip>>
My name is John Yates, and I have done extensive work with various load
limiting ìStitch Rippingî devices since the invention of the Screamerís
almost ten years ago. I thought I could shed some light on this subject
for those interested.

Dan (Osman) and I had many lengthy discussions on how to limit the loads on his
rope jump systems. We talked about the use of a Tyrolians, Screamers to
limit loads and use of High Strength Tie-off Pulleys to terminate the
rope ends. It is hard to believe that forces could be generated that
would ìBRAKEî a climbing rope if Dan had the system set up as usual. Dan
usually had Screamers set in the system in a tandem configuration (ie.
two side by side). This configuration would limit the load and the
Screamers would elongate if forces over 950-1000 lbf. were reached
during a jump. If the system was configured right there was a ìWEEK
LINKî ie. Screamers that would activate if forces reached any thing
close to a critical level. I hope the investigation will reveal how Dan
had his system set up, only then can we really speculate on what really

Anyway about Screamers.
Screamers are a stitch ripping device that allows forces to be
decelerated over a longer time interval than they would be if the
Screamers were not in the system. Standard Screamers or ICE-Screams are
configures from stitch patterns consisting of 6 rows of zigzag stitching
sewn into each wing of the unit. This stitching is done by means of a
computerized sewing machine. The machine can be configured to allow the
Screamer to activate basically anywhere between 1 and 650 lbf. We chose
to use an average activation of 550 lbf. because it seamed to be about
the right force to use as a upper limit for marginal protection and Ice
screws. Not every thing is a real science.

Some interesting things happen when you look at how much energy is
ìabsorbedî in the system when a screamer is used. If the ìTrueî
absorption is measured in a completely static system, lets say doing a
drop test with a steel cable and weight we will see that about 5-600 lbf
was absorbed by the stitch ripper(Screamer). When a Screamer though is
put in a system which uses dynamic climbing rope instead of static steel
cable the amount of energy which is absorbed is increase by 25-40%. We
see that the absorption of energy increases to 800-900 lbf. I can
attribute this extra energy we see being absorbed to the fact that the
ìDynamicî climbing rope in the system is allowed to elongate and remain
dynamic for a longer time interval than it would be, if there was no
screamer in the system.

An example: A dynamometer or load cell is placed on a bolt hanger. A
climber takes a fall which generates a fall with a factor of .5. This
generates a force of 2000lbf as seen on the dynamometer. When a
Screamer is hooked in the system below the dyno. the same fall only
shows a peak force of 1200 lbf. We know from extensive testing that the
Screamer can only absorb 500 lbf. So how do we account for the extra 300
lbf seen in this example???
The increased time interval(duration) of the fall allowed the climbing
rope to be more absorptive!!
Thus Screamers limit loads and dissipate energy over a an increased time
interval. This increase in the duration of the fall is most important
in a ìDynamicî systems because it allows the rope to do its job even
better than it was designed to do.

Stitch ripping devices have been used in many other areas besides just
climbing. Many industrial application have been developed for the use of
Stitch ripping devices. The most common is the Fall Arrest lanyard
which uses a woven type of screamer device to decelerate a industrial
worker if he falls in the workplace.

Over the last ten years I have worked on numerous projects with various
Aerospace companies such as McDonnel Douglas and Bowing to develop
various types of Stitch Ripper ìScreamerî type devices. They use them
to decelerate objects which seperate from one another during controlled
testing. The coolest project I worked on was a rocket fairing which was
to house a communications satellite during launch on a Titan rocket. The
fairing separation test was conducted in a vacuum chamber which took
about 120 rippers in an elaborate configuration to decelerate the
various parts of the fairing after the explosive bolts separated them.
Anyway the point is that climbers are not the only ones using this type
of technology to their benefit.

If any of the other physics nerds in this group would like to discuss
specifics on the use of Screamers in various climbing applications, I
would be more than happy to respond.


Yates Climbing Equipment

Strength of knotted runners

From: ratagonia@xxxxxxxxxxxxxxxxxxx
Newsgroups: rec.climbing
Subject: Tied Supertape Runner Strength Test
Date: Fri, 19 Mar 1999 23:29:01 GMT

Another test from the Black Diamond test lab. Since we tested tacked
supertape and tacked spectra runners girth hitched together, and found them
to be 70% as strong as a single tacked runner, I was curious as to how strong
a tied Supertape runner is. So I took the same spool of 11/16" nylon
Supertape and tied up some runners using a well-dressed water knot.

3-19-99 TD 14787
Results: ( all values in lbf )

3798, 4067, 4423, 4585, 3988. All broke where the web enters the knot.
AVG = 4172
sigma(n-1) = 323
Rating = 2911 ( Rating is AVG less 3.9*sigma(n-1) )

Compare to the Tacked runners in the same material ( TD 14742):
AVG = 5713
sigma(n-1) = 156
Rating = 5105

Results: 1. Tied Nylon Runners tested on average 73% of the strength of a
sewn runner in the same material. 2. Variance in a tied runner is pretty
high. The rating of the tied runner is only 57% of the rating of the tacked

Conclusions: 1.You lose a lot when using a tied runner. About the same loss
as when girth hitching them together to make them longer. 2.The tied runner
variance is pretty high. The knot 'system' is not a consistent system.

My Personal Opinions:
1.Tied runners are probably all right most of the time. After all, we've been
using them for years and we don't see many break in the field, do we?
2.I would be careful about tying runners out of low-strength materials like
9/16" supertape. Yeah, we thought they were strong. But they are not that

Tom Jones
BDEL Harness guy

Runner Girth Hitch Data from BD

From: Chris Harmston <chrish@xxxxxxxxxxx>
Newsgroups: rec.climbing
Subject: Runner Girth Hitch Data from BD
Date: Tue, 16 Mar 1999 17:28:36 -0700

As a followup to requests and slams from several rec.climbers Tom Jones
(ratagonia) has prepared some samples and I have had them tested. Here
are some results that will appear on Karl Lew's web page (I hope?).

All samples are BD product. All samples are pulled between 10 mm steel
pins at 4 inches per minute. Numbers expressed below are pounds force
(lbf) unless otherwise stated. "Location" is the location where failure
occurred. Stdev is the standard deviation (n-1).

I use mixed metric and english units. Sorry if you can't convert in your
head. I have converted the important ones for those who care. This
statement is added due to the New Zealand rec.snowclimber who slammed me a
month ago for not using metric units. Sorry, we live in a dual system so
deal with it.

Control Groups (this is what we sell, for those who care):

11/16" Nylon Supertape sewn loops (BD rating 22 kN = 4946 lbf).
5981....wap (web at pin)........5713 (25.4 kN)..156

5/8" Spectra sewn loops (BD rating 22 kN).
6281....tack (the sewing).......6173 (27.5 kN)..140

Question: Are BD slings weaker than our competitors? What do ratings on
products really mean? Why are BD runners rated at 22 kN (the minimum CEN

Answer: Some competitors slings are stronger and some are not. Ratings
are primarily marketing related. Stronger is supposed to be better,
right?. Basically, we have multiple types of runners that all pass CEN.
Different lots of material have different strengths. Different sewing
machine setups have different results. All this combines into a runner
program that requires frequent rating changes and multiple tags that need
to be inventoried and controlled. When we change a rating we have to
recertify it through our CEN certification body ($800 per product cert).
Rating all runners at 22 kN regardless of whether they are really stronger
is significantly cheaper than the lost sales due to the marketing
advantages of a higher rating. Irrelevant rambling on my part, sorry.

Runner Girth Hitched to another Runner (all components are sewn loops):

11/16" Nylon Girth Hitched to 11/16" Nylon
3536....wak (web at knot).......3991 (17.7 kN)..357

Spectra Girth Hitched to Spectra
4261....wak.....................4275 (19.0 kN)..240

Nylon Girth Hitched to Spectra
4063....wak (nylon).............3999 (17.8 kN)..208
3917....wak (nylon)
4231....wak (nylon)
3686....wak (nylon)
4100....wak (nylon)

Spectra Girth Hitched to Nylon
4284....wak (nylon).............4236 (18.8 kN)..115
4178....wak (nylon)
4064....wak (spectra)
4345....wak (nylon)
4310....wak (nylon)

1) These are variable systems. Multiple data points are needed in order
to be able to state real trends between groups. Don't base your
conclusions on single data points. This is my reservation of Karl's web
page. He paid for the samples so I can't fault him too much. I keep
asking him to give me more samples because I really love to break stuff!
2) 11/16" Nylon Sewn Runners are 93% of the strength of 5/8" Spectra
Sewn Runners on average.
3) Girth Hitching reduces the strength of the material by 30% on average.
4) Girth Hitching strength is more or less independent of what it is
attached to (at least for this test). Note the similar strengths between
Nylon hitched to Nylon or Spectra and Spectra hitched to Spectra or Nylon.
5) If you must link two runners a carabiner (krab for the Euro's) is
stronger. If you must use a girth hitch then girth hitch onto the weaker
material. In other words, make sure that the runner that has the knot is
the stronger one.
6) Karl has some new fangled knots that are stronger. See his web page.
7) Quite a long post for such a minor topic. Wasted two hours of my time
today. I hope it was worth it. I will probably have to make this time
up. chris

Chris Harmston (chrish@xxxxxxxxxxxxx).
Quality Assurance Manager. Materials Engineer BS, ME.
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552

Linked Girth Hitches

From - Sat Mar 6 07:50:37 1999
From: "Karl Lew" <karl_lew@xxxxxxxxxxx>
Newsgroups: rec.climbing
Subject: Linked Girth Hitches

Those of you who have been following the Girth Hitch saga
will be surprised to learn the latest development. The
linked girth hitch knot I show at www.best.com/~klew/knot.shtml
is actually *WORSE* than a girth hitch. The two samples
I sent Chris failed at 49%-56% of tested/rated strength,
depending on material (spectra/nylon and spectra/spectra).
Egad. Danger, Will Robinson!

Once again, many thanks to Chris and his staff at Black Diamond
for taking the time to pull test these knots.


DISCLAIMER: The results shown are derived from personal correspondence
and are in no way related to Black Diamond in any official way.

Re: Runner strength - TEST REPORT

From - Wed Feb 17 10:19:21 1999
From: ratagonia@xxxxxxxxxxxxxxxx
Newsgroups: rec.climbing

Can you guys spew, or what!

OK, enough philosophy, let me dig into the BD runner test files and see what I
can find.

9-16-98 Single Strand Test: Blue 11/16" supertape sample:

3418, 3396, 3385 avg = 3399 lbf == 15.2 kN

9-15-98 Loop & Dogbone tests, same webbing, cut 15", 5 tacks, 138 thread:

Loops: 9 samples, avg = 5810 lbf == 25.9 kN s.d. = 139 lbf
Dogbones: 10 samples, avg = 5822 lbf == 26.0 kN s.d. = 138 lbf

Lost strength = (2*15.2)-26 = 4.4 kN == 14.5% in this example.

Runner strength TEST REPORT 2

From - Wed Feb 17 10:19:54 1999
From: ratagonia@xxxxxxxxxxxxxx
Newsgroups: rec.climbing

Again, searching the BD runner test files, I think you all might be rather
put out by how large the variation in strength is in a simple item like a
brand new sewn sling. We have collected a lot of data over the years, but
let me just summarize one item:

5/8" spectra/nylon runners ( 3 lengths ). This raw material specs did not
change in this time period, though several different batches of webbing were
probably involved. The tacks and thread probably did not change, and break
point is usually at the pin. The test method probably did not change.

The data from batch tests is summarized on a graph. For each batch test of
3-10 runners, the high, low and mean are charted. Data from about 80 batches
are shown.

I look at the data ( on a graph ) for values from 5/9/96 to 7/7/97. I see a
range of values from a low of 5100 lbf to a high of 6900 lbf ( 22.8 kN to 30.8
kN ). The bulk of values are in the range of 5500 lbf to 6500 lbf.

While most batch tests have a range of about 800 lbs, a very few have as wide
a range as 1500 lbs. Each batch is made with the same webbing, tack pattern,
thread, humidity, operator, clamp, machine and probably needle.

So the "strength of a sling" is not that fixed of a value. We rate these
slings at 22 kN. And over the course of 14 months, we saw a strength range of
22.8 to 30.8 kN in individual pieces that we tested ( a range of 30% of the
total strength ). And there's the strength rating of the webbing... but
that's another topic.

HEY - these are my own, personal opinions and conclusions, and are not those
of my employer.

Jratus, Utahnus

Re: Runner strength

From - Tue Feb 16 11:00:12 1999
From: csoles@xxxxxxxxxxx (Clyde Soles)
Newsgroups: rec.climbing
Subject: Re: Runner strength

Mike Garrison <mike.garrison@xxxxxxxxxxxxx> wrote:

> I'm pretty sure it would fail somewhere between 20 and 40
> KN, and the sharper the bend the closer to 20.

Correct, probably around 25kN if normal biners are used and assuming the
stitching doesn't blow (big assumption if you sew it yourself). For
static breaking strength, the webbing (or rope) runs around very large
capstans (1 ft. diameter or bigger) so it has little real world value.

DISCLAIMER: Unless otherwise indicated, this post is personal
opinion and NOT an official statement of my employer.

Re: web-o-lette

From - Mon Feb 8 10:15:05 1999
From: steven@xxxxxxxxxxxx (Steven Cherry)
Newsgroups: rec.climbing

In <79mhn3$gar$2@news.seed.net.tw> "Mr. G" <mrgecko@xxxxxxxxxxxxxx> writes:

>Oh ye purveyor of webolette wisdom (aka Karl), do you find that the
>webolette is really long enough for anything besides the straight forward,
>everything is right there in a nice neat compact bunch kind of a belay
>setup? I'm tempted, but I fear the short (10 foot is what the website says)
>length. Please calm my fears.

The web-o-lette is designed for a two-piece anchor. The cordalette's
usual length is intended for a three-piece anchor. The web-o-lette is 10
feet. After tying the fisherman's, the cordalette is usually 16 to 18
feet. 10/2 = (roughly) 16/3. Even at 18 feet, with six strands, there's
only a six-inch difference at most.

As a sport anchor the web-o-lette is ideal and the cordalette is overkill.
As a trad anchor, the web-o-lette usually needs to be supplemented (of
course, sometimes the cordalette does too).

Is that fear-calming enough?


Real World Loop Strength

On Fri, 8 Jan 1999, Russ Walling wrote to Chris Harmston :

>Hi Chris,
>Had a few questions I was hoping you could help me with.
>Q: Say a cable or webbing is rated to X. Is there a quick and easy
>convert to find loop strength, assuming the bond is full strength? How
>about real world loop strength, as loaded between biners, not just

Most people would assume that the strength of a loop is twice the strength
of the single strand breaking strength. What I have found is that this is
not correct for two reasons. First is that the tack does factor in. It
is not always easy to ensure that the tack is stronger than the webbing.
So take off 5%. Second is that the single strand strength is obtained by
testing over large radii. Loops are tested over 10 mm pins. The pins
weaken the loop as you should expect. So remove another 5%. What I find
is that the loop strength is about 10% weaker than 2 times the single
strand rating. This is plus or minus 5% or there abouts.

>Q: same Q as above, but instead of a loop, a rabbit runner config, ie:
>loop at each end, single strand in the center. Load applied in each

Here the tack does not factor in as much. Only the effect of the pins.
So take of 5%. This is pure assumption because I have not looked at this
data myself (even though we had rabbit ears in the bivy and Big Wall I
tent-we use loops now).

I forgot to answer the carabiner runner question. Basically the biners
are like a 10 mm pin. Sometimes the radius of the biner is too curved and
then the runner breaks even lower. Also, wide runners put greater load on
the carabiner gate side and biners are found to break significantly below
ratings when tested with wide runners.

Chris Harmston (chrish@xxxxxxxxxxxxxxxxx).
Quality Assurance Manager. Materials Engineer BS, ME.
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552

DISCLAIMER: Unless otherwise indicated, this correspondence is personal
opinion and NOT an official statement of Black Diamond Equipment Ltd.

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