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:

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.

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.

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. 

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.  

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.  

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.

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. 

  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.  

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.

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:

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.

  Sewing it up before the "heel-hook dyno" on Sykes Sickle, Spearhead, RMNP

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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