Source: www.spadout.com
Climbing anchors are a collection of protection (bolts and / or trad gear) which are equalized and redundant. Climbing Anchors are built to protect the leader when belaying a second or to use as a top rope anchor.
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One of the complications about explaining how to setup climbing anchors is that every anchor is unique. The available protection, direction of protection, what gear you have left (now that you have led a pitch), and your requirements (depending whether it is a top rope anchor or you will be leading above it) all affect how you build your anchor.
Therefore, developing a 'box of tricks' and understanding a variety of anchor building techniques is key.
SARENE
SARENE is a good rule of thumb for building anchors. SARENE stands for Solid Anchors, Redundancy, Equalization and No Extension.
Solid Anchors
'Solid anchors' means that anchors must be 'bomb-proof'. Make sure you place solid protection that is multi-directional. The anchor cannot 'pop-out' if the belayer is pulled up due to a leader fall. Make sure the protection is placed in solid rock that will not break or 'flex' under pressure.
Redundancy
Always design your anchors so that it will still hold if one (or two) pieces of protection fail. Most anchors are built with three or more pieces of protection. Anchors should be constructed so that they will hold even if one piece of protection fails or one piece of webbing / cordlette is cut.
There are a few exceptions to the concept of using three pieces of protection. Two quality bolts are considered safe in many climbing areas. A large live tree, 12 inches in diameter or greater, is also considered safe in many areas. When using trees girth hitch a tied runner (made by tying webbing with a water knot) to the base of the tree. Always girth hitch the tied runner to the lowest part of the tree (to reduce leverage).
Equalization
Make sure that every piece of protection receives the same amount of force.
Cordlette
An easy way to equalize forces is to use a cord-o-lette (a 20ft piece of cordlette tied in a loop using a double fisherman's knot). Full details: Cordlette.
The Sliding X
The sliding X is an auto-equalizing system that will equalize if you shift your body weight. The Sliding X is created between two pieces of protection using cordlette or webbing. (Note: The following diagrams only show one carabiner for clarity. Always use two carabiners for redundancy.)
The most important element of the sliding X is the 'twist' which is added when setting up the sliding X.
The 'twist' is created by taking one side of the webbing (or cordlette and twisting it 180 degrees creating a loop. Then clip the biners through the loop and the other side.
The importance of this twist is illustrated below.
American Triangle
The above image is incorrect and deadly.
If you leave out the twist and one side of the anchor fails, the biner will slide down the webbing (or cordlette) and fall off the end of the webbing (resulting in complete failure). The twist places the biners through the center of the cordlette therefore prohibiting the biners from completely failing. Though complete failure will not occur (presuming the remaining piece of protection does not fail), the anchor will be extended.
Advantages
- Auto-equalization and dynamic
- Fast setup
- Minimal gear requirements (a double length runner will do the job)
- - Extension will occur if one side fails.
- - You have to setup multiple 'Sliding X's if you want to use more than two pieces of protection.
Sliding X with Minimal Extension
Advantages
- Minimal gear requirements (a double length runner will do the job)
- Reduces extension (compared to standard sliding X).
- You have to setup multiple 'Sliding X's if you want to use more then two pieces of protection.
- The dynamic equalization properties of the 'Sliding X' are removed.
No extension means that if one piece of your anchor fails your anchor will not be 'extended'.
An easy example is the Sliding X. If one side of the 'Sliding X' fails the biners will be dropped 1/2 the length of the cordlette until the biners will be 'caught' again. The acceleration will increase forces on the remaining portion of the anchor (Force = Mass * Acceleration). This increases the risk of the remaining gear failing.
The importance of Angles when setting up anchors
To minimize force, minimize angles. When equalizing two pieces of protection, use angles below 60 degrees.
The graph shows the weight distribution for any given angle. 20 degrees or less distributes 50% of the force to each piece of protection. 60 degrees distributes 58 percent of the force to each piece of protection. 90 degrees distributes 71 percent of the force to each piece of protection. 120 degrees distributes 100 percent of the force to each piece of protection.
Angles greater than 90 degrees create dangerously high forces.
Force on each piece of protection = (total force)/[2 cos(q/2)]
Multidirectional Anchors
Though 'SARENE' is a good reference when setting up an anchor there are many other issues to consider. When you are climbing multipitch climbs (climbs longer than one pitch) you have to consider upward as well as downward forces on the anchor. Upward forces on the anchor are created when the leader falls and has placed in one or more pieces of protection on lead.
Considering upward forces is especially important when using Passive Protection passive or natural protection. Natural protection is when you sling horns or other natural rock formation. Though slinged horns can create excellent downward protection, they risk being pulled out of place if the belayer is pulled up. Passive protection is typically only suitable to protect one direction.
The solution is to place protection below the anchor designed to protect against upward movement. Attach this piece to the anchor. Active protection are often multidirectional by themselves and will not necessarily require an upward directional.
Redirecting the Second
A popular means of belaying the second while climbing is to belay off your harness. When you belay off your harness and the second weights the rope the weight will pull straight down on your harness.
This can be very uncomfortable and difficult to hold. Redirecting this weight is worth a few seconds of your time.
When belaying the second from your harness place a carabiner on a solid piece of protection (a piece from your anchor is fine). Run the rope from the second, through the biner and then to your belay device. If the second falls a low upward force will be created (similar to belaying a climber on top rope).
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