Anchor (climbing)

In rock climbing, an anchor can be any way of attaching the climber, the rope, or a load to rock, ice, steep dirt, or a building by either permanent or temporary means. The goal of an anchor depends on the type of climbing under consideration but usually consists of stopping a fall, or holding a static load.

Types of anchors

Depending on the material being climbed, there are many types of protection that can be used to construct the anchor, including natural protection such as boulders and trees, or artificial protection such as cams, nuts, bolts or pitons.

Natural anchor

A natural anchor is one that does not require man-made climbing gear. Such anchors may consist of trees, chockstones already lodged in a crack, horns and protrusions, etc.

Artificial anchor

An artificial anchor consists of man-made climbing gear placed in the rock. Such gear may be spring loaded camming devices, aluminum chockstones, steel expansion bolts, pitons, etc.

Belay anchor

A belay anchor is used as a sole attachment to the cliff face, to support a belay or toprope. It should ideally be essentially foolproof, consisting of multiple redundant components (natural and/or artificial), none of which are likely to fail, and none of which in the event of failure would cause the entire anchor to fail. Any one component of a good anchor should be able to support the entire system by itself.

Running belay anchor

A running belay anchor is used as a safeguard in the event of a fall while lead climbing. Often hastily placed in the stress of the moment, these anchors are not as secure, or bombproof as belay anchors and cannot be relied on as sole attachment points to the rock. Running belay anchors must be backed up by other running belay anchors below should they fail.

Ice anchors

The ice picket is used as an anchor in mountaineering. It is driven into the snow and used to arrest falls.

Attachment to the anchor

Indirect

When the rope goes from the climber to the belayer. Most often used under controlled circumstances at climbing walls or when the climber doesn't have the weight advantage on the belayer during bottom roped climbs. It is impossible to escape from the system.

emi-direct

When the rope comes from the climber to the belayer, but the belayer is attached separately to an anchor. Often used when multi pitching and the belayer is on a stance. Or when top roping and it is possible that if the climber falls the belayer will be pulled from the stance above the climber. The belayer can, with a little effort then remove themselves from the system if required.it is essential that the belayer is attached to the anchor via the belay loop at the front of the harness. Attaching the belayers harness to the anchor via the back of the harness can cause the harness, when placed under strain constrict inwards elongating front to back, rather than side to side. This can result in crushed pelvis' and serious harm to the belayer.

Direct

When the rope comes from the climber to an anchor. A hanging belay device may be used, although it is common in this instance to just use an Italian hitch. The belayer is totally free of the system.

Equalization

Anchor equalization is the process of combining two or more anchors in the build of a single equalized anchor. This is the method used in a redundant belay anchor, as mentioned above. If assembled correctly, the load can be distributed amongst the individual anchors, rather than placing all the load on a single anchor point. This decreases the chance that any of the anchor points will fail, and, if a point does fail, the other(s) should still be able to hold.

When forming an equalized anchor, it is important to take into consideration the angle formed between the two pieces of protection -- the "V-angle". One must try to minimize this angle as much as possible, because the greater the V-angle, the more force will be placed on each piece of protection.As shown below, if the V-angle is greater than 120 degrees, the load on each anchor comprising the equalized anchor will actually be greater than the load on the rope connected to the equalized anchor. This is a hazardous situation which makes it worse to use equalization than not at all, and should be avoided.

If the load force ("To load" in the image at right) is $F\_\{Load\}$ and the V-angle is $heta\_V$, then the force on "each" anchor is given by:

:$F\_\{Anchor\}\; =\; frac\{\; F\_\{Load\}\; \}\{\; 2\; cos(\; heta\_V\; /\; 2\; )\; \}$.

Resulting from this expression, we can deduce:
*At a V-angle of 30 degrees, each of the two anchors bear a force of about 52% of the original load.
*At 45 degrees, each anchor bears about 54% of the load.
*At 60 degrees, each anchor bears about 58% of the load.
*At 90 degrees, each anchor bears about 71% of the load.
*At 120 degrees, each anchor bears a force equivalent to 100% of the original load. An angle this large should never be used.

References

* Long, John (1993). "How to Rock Climb: Climbing Anchors". Chockstone Press, Evergreen, Colorado. ISBN 0-934641-37-4
* Graydon, Don, and Kurt Hansen, eds. (1997). "Mountaineering: The Freedom of the Hills", 6th edn., pp. 143-152. The Mountaineers, Seattle. ISBN 0-89886-427-5