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What's the force on your anchor? |
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The three ways to load an anchor.
redirecting off the anchor
Force vs. Strength in the Anchoring
Equation
Where we attach the belay device and climber's end of
the rope
(directly to the harness or anchor or both) has a big effect
on the
loads that are actually applied to the anchor as the result of
a fall.
Depending on the environment and
the forces we
anticipate, there is an opportunity to choose the
belay method most
appropriate for the anticipated falling
forces.
Anchor failure is
clearly not an option in technical climbing and so understanding
how the belay set-up correlates to the
loads placed on our anchor can
be paramount to our survival in the vertical world.
The primary environmental variables in this
equation of Force vs. Strength are:
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1.
The amount of force generated: lead fall, seconding fall,
pendulum, shock load, free hanging, slab, low friction, etc.
2.
The anchoring materials: good bolts, bad
bolts, screws, pickets, small wires, cams,
trees, slings, cords, etc.
3. The
anchoring medium: snow, water ice, alpine ice, solid rock,
less-solid rock, etc.
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How strong is the anchor?
The reliability of each piece of protection and its
true
strength can be relatively predictable in
solid rock. Less solid rock
and all of the other mediums (snow, ice, etc) that we may
rely on for
our protection systems can be very unreliable and/or
unpredictable,
especially in the mountains and so the quality of the pro
might encourage many placements in the softer rock
types..
Once we have sufficient quality
and quantity
of protection pieces, we must decide how to best equally load
each
component and the result will determines the total
strength of our
anchoring system. There has always been debate as to which
anchoring
system is the best, as best might mean strongest,
but it could also
be the most time efficient, or the simplest, or less affected
by
shock-loading, or better self-equalizing, or the best that you
can
construct with limited resources, or perhaps
even less impacting to the
environment is "best".
"Strong-enough" might be the best descriptive
as there is ultimately no objective or completely calculable equation
to determine precisely what the strength needs and capabilities are in
most anchoring situations, as the strength of the medium is
highly
variable and difficult to determine an absolute quantity.
Redundancy and multiple anchor points can be necessary
and this can
involve creative strategy in figuring out how to maximize the strength
of the system that is created by connecting together these protection
components.
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Often, the strongest option is to
belay off of the body = less force on the anchor.
Belaying directly off of the body/harness reduces the
peak force on
the anchor to less than a theoretical "1" in an equation where "1"
equals the actual force created in a fall that is
actually transmitted
to the belayer.
By belaying off the body, we can best minimize
the force applied to the anchor and thus reduce the
potential for anchor failure.
When the strength of an anchor is
less reliable due to fractured or
weak materials (rock/ice) or the quantity of anchor points is
minimal relative to the forces anticipated, the best choice of belay
technique is the oldest, simplest, and strongest.
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Belaying the leader or second directly off
of the belayer's body
which is connected directly to the "master-point" or most equalized
part of the anchor, with no slack or angles between the anchor,
belayer, or climber A-B-C in a straight line is the ideal
equation.
A century ago, most
belayers were unanchored at the top of a pitch and only by
using body
position, angles, and friction to their advantage, were they able to
hold the falls of the second.
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The
modern method of a "direct belay" on the
anchor: 1 = 1
To belay directly off of the anchor, we
need only to be sure that
the anchor is fully capable of holding the falling forces without a
doubt.
Modern bolted anchors are easy to trust in
this situation and
most trad anchors in solid rock are reliable enough
to facilitate use
of the "direct belay" method.
With a theoretical falling force
of "1"
is applied directly to the anchor, the same force of "1" is
absorbed
by the anchor.
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This method is typically only used for
belaying the
second climber from above where forces are generally moderate and the
anchor is strong enough for the anticipated loads.
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There are many advantages to belaying the
second directly off of
the anchor: ease of use is one of the best reasons and this method can
also facilitate speedy transitions, proper nutrition and fluid intake,
better communication, and a better belay due to the belayer being "out
of the system" in a way that facilitates a "big picture" perspective
and better risk management as a result.
The upper locking carabiner is
connecting the belayer to the anchor and the lower locker connects the
auto-lock belay device
We are not yet applying the "direct anchor
belay" technique to the
belaying of a lead climber, especially in a "trad" application
where
the strength and reliability of the anchor pieces might be less than
ideal, especially where the highest forces are likely
to be generated.
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In the lead climber situation, a belay directly off of the
body
is still the best way to minimize the falling forces that are
applied
to the anchor.
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Re-directing the belay through the
anchor: Why multiply the falling force?
The redirected belay describes the method of belaying
off of the
body, but rather than the rope going directly down the cliff to the
second, it is "redirected" through a separate carabiner
on some part
of the anchor (preferably
the master-point).
When we apply the same equation to the redirected
belay method, we see that what seems to be a benign change of direction
that reduces some of the force on the belayer (the only advantage),
also adds forces to the anchor.
A falling force of "1"
is the same on
either side of the redirecting carabiner (minus friction) and this
"pulley effect" combines to put multiply the falling forces by
1.6 to
1.8 on our anchor, not quite doubling but definitely
adding substantially extra force to the anchoring system.
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The re-directed belay method adds extra force to
our belay in a
manner that almost doubles the forces applied to each component of our
anchor system. The belayer also works harder to
pull rope through the
friction of the carabiner.
For some reason, this antiquated method remains a
favorite among
the crags that I visit regularly and likely this is a
result of "old
thinking" and maybe a tendency towards stubbornness in climbers as it
takes a bit of tenacity to cling to a steep cliff or frozen wall of
water - a trait that serves us well in many situations but can prove to
be a hindrance in learning and adapting to new environmens and
discoveries.
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How to prevent anchor failure: Quality,
quality, quality.
Certainly the choice of belay method has a significant
effect on
the likelihood of an anchor failure but there are other important
qualities that make a big difference:
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1. For lead falls, a rope that is rated with
a lower impact force,
which is usually thinner (9.1-9.5 mm) or better yet, a
"double rope
system" of < 8.4-6mm ropes in which each rope
is clipped independently
into seperate protection pieces are more
energy absorbing than thicker
or higher impact force rated ropes.
Newer ropes are also much more energy
absorbent than old ones and this
is a cheap investment in a stronger protection system.
2. Taking the time to place very solid gear
in the best rock may
be difficult, but without quality trad placements, no equalizing
technique will make bad pro any better.
Although they may not place as
much gear on a 5.8, if you watch any "trad master" on a hard lead, you
will see lots of gear going in the rock, often a piece or two every
body length: shorter falls create less force than longer ones.
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Sewing it up before the
"heel-hook dyno" on Sykes Sickle, Spearhead, RMNP
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3. A quality belay for the second
can make all the difference.
For top-roping, a snug-enough rope on the second and good directionals
on traverses will help minimize the potential for
shock-loading as the
result of slack in the rope system. Pendulum falls can be a
source of
significant slack and create higher forces as a result.
Placing extra
gear if possible on traverses and will help
minimize this potential
force.
4. A quality belay
method for the leader that helps minimize
forces on the anchor (and lead gear) is the less understood
"dynamic
belay". One dynamic belay method involves
the belayer letting rope run
through their belay hands (leather gloves helpful) in the
event of a
fall and braking slowly to reduce the shock-loading effect of a locked
belay device.
In the other dynamic belay method, the
belayer locks-off
the belay device and then makes a small leap upward when the falling
leader's force reaches them. Both of these techniques will
result in a
longer lead fall and so might not be appropriate in situations where
the result would be impact with a ledge or the ground or cause further
injury (such as on a slab). If you've ever used a dynamic
belay or
been caught by one, you'll agree that there is a noticeable difference
in how much "softer" the whole belay system feels and
functions.
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