There's a lot of
inaccurate beliefs in the climbing
world. Is hardware
ruined after dropping it? Will a clove hitch slip?
Will the Euro Death Knot invert during a rappel?
How often do you accept what you
hear
without taking a hard look at the tests?
This
page is dedicated to getting things straight. Most
of what
you'll read there is based on actual pull tests conducted by myself and
Jeff Fassett, an AMGA Certified Rock Instructor here in Tucson.
In other cases, we've directly contacted individuals who have
conducted controlled tests themselves.
How am I qualified to bust these myths?
Judge for
yourself. A lot of the time I've done research on what
super-seasoned, intelligent climbers have tested themselves.
As
for my
credentials: I'm an AMGA Certified Rock Instructor, I have multiple degrees involving
research, thousands of days in the field, a really good head
on my shoulders, and lots of training from recognized experts.
Keep in mind a few things:
I've edited most of the anecdotes to keep
them succinct.
It's only necessary here to present the facts, not
lengthy periodical-like papers. But don't
assume that
hasn't crossed my
mind.
If you're questioning what you read below, good.
Think
critically. Test things yourself in a safe
environment.
Nothing is better for
building your confidence than your own experience.
If you'd like, submit your questions/suggestions/myths via
email by clicking
the contact link above. We'll see if we can test it out for
you.
Myth 1: Carabiners are fragile
Myth: "Carabiners are susceptible to
hair-line fractures if they are dropped. These fractures cannot be seen
by the naked eye, but can drastically weaken a carabiner. So NEVER DROP
YOUR CARABINER. If you do, it is best to discard it immediately and
replace it with a new one." (source:
http://www.cbcnsw.org.au/docs/AbseilGuidelines.pdf)
Reality: This is not true of modern
carabiners. First, the "grain" of the aluminum runs parallel
to the
stock, not perpendicular, so undetectable hairline fractures
spontaneously causing carabiner failure just isn't true. Steve Nagode,
a quality assurance engineer with REI, conducted an experiment in which
carabiners were dropped six times from a distance of 10 meters onto a
concrete floor. The breaking strength of the carabiners was
then
determined with a 50-kN load cell. The results: no reduction in strength was
observed when comparing the dropped carabiners with carabiners that had
not been dropped.
Black Diamond's website says this: "It's best
to
inspect dropped gear for dings and significant trauma. If only light
scratching is visible and gate action is still good, there is a good
chance it is fit for usage."
Here's a more colorful test, this time done with a Petzl
Reverso: I call this "Reverso VS .357
Magnum". Shooting a small object with a snubnose .357 from a
safe
distance
is tricky, but yields thrilling results. This
is akin to throwing the Reverso into a rock surface at 67m/s,
which would
require dropping it 240m (790 feet).
And these calculations omit air resistance,
which limits the
terminal velocity of the Reverso free-falling to around 35m/s (the
terminal velocity of a baseball). In actuality, the piece of
gear
would not reach 68m/s even falling this far. The Reverso bent
various
ways, but it took 5 direct hits before it actually broke.
This seems to indicate that a single, short drop for a piece
of hardware does little to no damage.
Myth 2: Nonlockers and Reversos mix
On two recent occasions, I arrived at
belay stances and found that I was being belayed with a Reverso
directly off the anchor, but with a NON-locking carabiner on
the ropes. (see the photo below).
Reality: While the chances of the rope coming
unclipped
are extremely low, i strongly discourage this practice. Any time a person's life is
dependant upon one carabiner, it's best to use a locking carabiner.
This includes rappelling, tying in to an anchor, and use in
a plaquette device. Consider this carefully:
in the
(unlikely) event that the rope is unclipped, the belay will
fail.
In a critical application such as this, use of a locking
carabiner will further reduce the chance of the rope escaping the
device.
Note, too, that the instructions for the device (shown below)
illustrate use of a locking carabiner.
Myth 3: Dyneema is a good material for
friction hitches
(Submission from Bill Holman, Pittsburgh, PA) - "Geir, I
have heard a rumor that dyneema is bad to use for an autobloc,
as the strong thin material can cut through ropes. Myth? "
Reality:
The dyneema will not cut through
the rope if used as an autobloc. I have tried this out on
multiple occasions. There are two big concerns that I have
heard when
using
Dyneema (or any other spectra sling) for an autobloc:
1) The biggest concern is that Spectra produces much less
friction than
nylon. In "Comparative Testing of High Strength Cord" by Tom
Moyer, Paul Tusting, and Chris Harmston, the authors found that the
autobloc grip strength of Mountain Tools Ultratape (a nylon/spectra
blend) was about 1/5-1/10 as strong as cords with a nylon cover.
The thin dyneema slings I have tested since Bill asked this
question are quite slick; I found them slipping under body weight
when
wrapped 5-6 times around a new rope. A 5.5 mm nylon cord
under the same conditions gripped very well.
2) The melting point of spectra (297 F) is significantly lower than the
melting point of Nylon-6 (Perlon) at 428 F. Spectra rapidly
loses
strength above 257 degrees Farenheight. So there's a greater
chance of weakening your spectra slings for subsequent use if you use
it
for an autobloc. The question is, however, how hot does it
get under an autobloc sliding along a rope? Well, I checked
this
out, too. It was a pain in the neck, but using a meat
thermometer
I found that the temperature under an autobloc on a single-rope rappel
of about 100 feet does not go above 120 degrees F. So melting
does not appear to be an issue.
Based on these initial findings, it's probably best NOT to use dyneema
for an autobloc.
Myth 4: Clove hitches slip under high loads
Many climbers use a clove hitch to tie in to the anchor during
multipitch climbs. One myth about the clove hitch is that it
will slip under load, and that both strands need to be loaded
for the
knot to be stable.
Myth: "Used as a traditional hitch, that is loading only one
end, the clove
hitch is liable to slip. It requires a load in each direction in order
to be effective, such as when being used as a crossing knot." (source:
http://en.wikipedia.org/wiki/Clove_hitch)
Myth: "The drawback of the clove hitch is that it can slip,
creep up the
carabiner, and open its gate ... if allowed to go unsupervised, the
knot is extremely dangerous." (source:
http://books.google.com/books?id=3Ohpsz6jP8cC&pg=PA40&lpg=PA40&dq
=clove+hitch+slip&source=web&ots=BbHlLZzmL3&sig=RgHr8P8uLxxksAyZ6dDu-o2-g7s)
Reality:
While clove hitch intially allows a small amount of rope to slip as it
tightens under load, it does NOT slip when
pulled to failure. Jeff Fassett and I pull tested a clove
hitch
tied around a carabiner with a 9.6mm rope. After setting the
knot
by
pulling on both strands, it was pulled to 1150 pounds.
Tape
marking the load strand had moved only 5 inches from its original
location next to the carabiner. The clove was then pull
tested to
failure. No
slip occurred as it was pulled to higher loads.
The rope broke at the clove hitch at 2700 pounds.
"Before" photo: note that a piece of tape marks the load
strand prior to pull testing
Here is the video of the pull test:
"During" photo: note that approx 5" of rope has crept through when
loaded to 1150 pounds. No
further creep occurred when the clove hitch
was pulled beyond this load.
"After" photo: the clove hitch ultimately failed at 2700 pounds.
The mechanism of failure is a familiar one: the
rope is severed at its entry point into the clove hitch.
Myth 5: The Euro Death Knot can roll during a
rappel
The Euro Death Knot (flat overhand) is gaining wide acceptance
among the climbing community as a means of joining ropes for
double-rope rappels. However, I still run into
climbers who
believe
that it's prone to rolling under rappel loads.
I've found only one documented case in which a climbing party
claimed that a flat overhand "untied itself" during a rappel
(9/12/1997, Guide's Wall, Grand Teton NP). In this
case, the
knot was untied and then "retied" just before the accident.
Countless
pull
tests and probably a million rappels since then have failed to
replicate what
happened.
Quite a few tests, however, have demonstrated that the flat overhand is
quite strong.
In 2000, Burton Moomaw, an AMGA Certified Rock
Instructor, pull tested
the flat overhand tied in two single dynamic lines. He found
that the knot inverted at 1400 pounds, then did nothing further as it
was subjected to higher loads. (Source: direct
communication)
In 2005, Jeff Fassett (also a Certified Rock
Instructor), completed an unusual and
humorous test on the flat
overhand. After using a flat overhand to tie a dynamic line
in a continuous loop, he dragged a 6,000 pound van with it.
The van was in park with the emergency break on!
Based on the vehicle weight and the friction of the tires, he
calcluated the load on the knot to be 1500 pounds. The knot
did not invert or slip.
He repeated the test using the flat overhand to join an 8.5mm
rope and a 10.5 mm rope. Again, the knot neither failed nor
inverted. (Source: direct communication)
Tom Moyer performed a series of tests on the
flat
overhand. He found that properly
tied and set flat overhands did not roll until loads
of 1400-2400 pounds were applied.
If the ropes were soaked and of significantly different
diameters, he found that the knot could initially invert at a
load
of 950 pounds. However, subsequent inversions
required
1070-1400 pound loads. (Source:
http://www.xmission.com/~tmoyer/testing/EDK.html)
It is
difficult to produce loads of even 600 pounds on a rappel.
Jeff Fassett and I measured the force produced on an anchor
during a double-rope rappel using a dynamometer. Not
surprisingly, during normal rappelling the force on the anchor was
simply body weight (in our measurements, 150 pounds). In this
case, the load on the flat overhand is 75 pounds. Even with
rigorous
5-foot deadfalls close to the anchor, e
anchor, we were unable to produce a load greater
than 600 pounds on the anchor. In this case, the load on the
flat overhand
is only 300 pounds. (These tests were conducted with
a
heavily-used 10.2 mm Beal dynamic line and a 150 pound person.)
Based on these measurements, the following conclusions can be drawn:
The
flat overhand is about
18 times stronger than it needs to be for rappelling when using two
single, dry ropes, and rappelling normally.
Very agressive rappelling may cut this margin down to
a 5-fold difference.
Under the worst of conditions tested (two soaking wet
ropes of different diameter), the flat overhand is
still 12 times stronger than the anticipated load on the anchor.
Very agressive rappelling may cut this margin down to
a 3-fold difference.
Even if the "roll load" of the knot is exceeded, it
would
take repeated, increasing loads to cause additional knot inversions.
