Technical rope work is both a science and an art. It’s a balancing act between situation, simplicity, efficiency, and proven understanding. Anchoring is an excellent example of this. Every system, if fully understood and applied correctly, is valid, but to use only one system without considering situational factors is limiting and shortsighted.
If each anchor point within the system is bombproof, it almost doesn't matter what style of anchor system you use. But in real-world situations, with suboptimal anchor points, need for more effective stance management, or situations where the anchor needs to accommodate multiple directions of loading, there are certain anchor types that perform better than others.
COMMON ANCHORS
Three-point sequential, pre-equalized anchor.
Pre-Equalized
The classic pre-equalized anchor (Fig. 1) is the most commonly used sequential anchor system. It's clean, quick to tie, redundant, efficiently uses material, has a well defined masterpoint, and has no extension of the masterpoint if there is an anchor arm failure.
The main problems with the classic pre-equalized anchor system are potential unequal and unpredictable load distribution.
The length of anchor arms and the amount of material in each anchor arm (single strand vs. a loop) affect load distribution due to variable amounts of material elongation (stretch) in each arm. This can create a situation where the shortest anchor arm of the system receives a significantly greater portion of the overall load, putting more load onto an individual piece in the anchor system.
As mentioned above, with high quality anchor points this may not be an issue, but with less than ideal placements this could lead to anchor point failure and potentially catastrophic complete anchor failure.
Distributive
Two-point self-equalizing, sliding X anchor.
Distributive anchors theoretically distribute the overall load evenly to all anchor points within the system, reducing the likelihood of a single point failure, and can accommodate multiple directions of pull at the masterpoint.
The self-adjusting nature of the masterpoint allows a wide range of motion which can compensate for directional changes. The "sliding x" (Fig. 2) is the most common of the traditional distributive anchors.
With this style, however, anchors consisting of more than two anchor points can increase friction and prevent effective load distribution, extension of the masterpoint if there is anchor arm failure, and redundancy in the material.
The Equalette anchor, a hybrid that blends components of sequential and distributive systems.
The Equalette
The Equalette is a hybrid anchor that blends components of sequential and distributive systems. It addresses many of the problems of both the classic pre-equalized and distributive anchor systems.
The Equalette maintains redundancy throughout the entire system, loads points within the system more predictably and has the ability for the masterpoint to shift when there is load change. One of advantage of the Equalette is that it always loads at least two anchor points within the system at any given time.
In a three point Equalette there will be one leg in the system that theoretically receives 50-percent of the load. Even while improving upon the issues associated with pre-equalized and "sliding x" anchor systems, the Equalette still presents challenges to users.
The sequential side (the pre-equalized legs) of the Equalette has the problem of uneven arm lengths affecting load distribution and the system also suffers from friction at the masterpoint. The masterpoint is less defined compared to the classic pre-equalized anchor, which can be an issue in multi-pitch stance management when clipping multiple carabiners to the same masterpoint.
The Equalette is a step forward in anchoring construction, but is not the end of the evolution of anchor systems.
The Quad
The Quad is a newer distributive style of anchor system that addresses redundancy by incorporating multiple isolated strands of material that guard against system failure due to cutting of individual strands.
The Quad utilizes a "straight V" inside the "quad pocket" which gives it similar load sharing qualities at the masterpoint as the Equalette. With a two-point anchor, each anchor point receives as close to 50-percent of the overall load as possible, decreasing the likelihood of anchor point failure.
Both the Quad and the Equalette have a certain amount of extension that is inherent with any distributive or hybrid anchor system. Extension can be managed with the thoughtful placement of limiting knots. The more that extension is limited the more the lateral range of the system is reduced.
When encountering multiple two point anchors, like on multi-pitch rock and ice climbs, the Quad can be pre-tied and used repeatedly for efficient transitions. The Quad can also be used with three and four point anchor systems with a few variations. When used in this configuration, the Quad becomes the next step in the evolution of anchor systems beyond the Equalette.