American death triangle
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The American Death Triangle, also known as the "American Triangle"[1], "Death Triangle" or "Triangle Anchor"[2] is a type of rock climbing anchor infamous for being a poor anchoring technique due to both the way the forces of the load are magnified on the fixed anchors and the lack of redundancy in the cord.
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[edit] Description
In a two-point climbing anchor, there are three carabiners: one at each fixed point and one at the "focal point" or where the load is going to be attached to the system. The goal is to distribute the force of the load so that each fixed point takes a portion (ideally an equal portion) of it. The anchor is formed by clipping a piece of webbing or cord through each of the carabiners in turn. The resulting triangle shape gives the anchor its name.
The force on each fixed point depends on the angle at the focal point. In the following table the percentage of the load's force that is transferred to the fixed point is listed at each focal point angle, and the same percentage is presented for the standard "V" shaped anchor.[3]
| Bottom angle | Load per anchor (V arrangement) | Load per anchor (triangle arrangement) |
|---|---|---|
| 0° | 50 lbf | 50 lbf |
| 30° | 52 lbf | 82 lbf |
| 60° | 60 lbf | 100 lbf |
| 90° | 70 lbf | 130 lbf |
| 120° | 100 lbf | 190 lbf |
| 150° | 190 lbf | 380 lbf |
Values for other angles and/or weights can easily be found using a parallelogram of force.
Aside from the magnification of forces, the death triangle violates several rules of thumb for building rock climbing anchors, such as
- redundancy: if the webbing fails on one leg of the anchor, the entire anchor will fail.
- extension: if one of the anchors fails, the webbing will extend and will shock load the remaining components of the system
An alternate bad form of anchor that has also been called the American Triangle involves using a single loop of cord that passes through two anchors and a carabiner, but the carabiner is not topologically bound to the cord. The correct method involves putting a twist in the cord as it goes through the carabiner, so that if an anchor fails, the carabiner will not slide off the cord.
There are situations where a climber may want to use this technique, but they are rare and require an expert to evaluate whether it is warranted. In summary, in a situation where the climber needs opposing forces to either keep passive chocks, camming devices, or spring loaded camming devices in a certain orientation (ie: a crack), they may elect to rig a triangle to create the opposing forces necessary to keep the protection in the correct orientation.[4]
[edit] Notes
[edit] References
- Long, John (1993). How to Rock Climb: Climbing Anchors. Chockstone Press, Evergreen, Colorado. ISBN 0-934641-37-4.
- Mountaineers, The (2002). Mountaineering: Freedom of the Hills, Fifth Edition, The Mountaineers, Seattle, Washington. ISBN 0-89886-309-0.
[edit] See also
[edit] External links
- Climbing Anchor
- CLIMBING.COM - TECH TIPS contains diagram
- Climbing Anchors includes photo
- [1]includes photo of second type of American Triangle
