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Climbing Protection System
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| Anchors Part 2 |
Artical
Number:26 |
| Overview: |
Anchors can be separated into several basic construction categories:
- Single Point Construction
- MultiPoint Construction
- Independent
- Series
- Self Equalizing
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Single Point Construction
Single point anchors consist of one piece of protection only. These may be a
piece of artificial protection or a strong natural feature (tree, boulder, horn,
chockstone, etc.). Single point anchors are often used in conjunction with a
body brace belay. In this way the system has some redundancy.
When to use single point constructions
A single piece of equipment (i.e. bolt, piton, ice screw, stopper, cam, etc.)
or strong point of natural protection may be an appropriate single point
anchor when:
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Loads are carefully assessed and predictable.
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Loads are low (~body weight).
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Direction of force is assessed and predictable.
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A slip (not a fall) is anticipated.
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Strength and security of the placement is carefully evaluated.
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A single point may be used to back up a body brace.
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Massive points (e.g. large tree, outcrop, horn, etc.) may be considered the
equivalent of a multi-point anchor in some circumstances.
Creating single point constructions
In the case of massive single points, a sling or the rope is wrapped around
the point and tied off. When possible and practical, slings should be doubled
throughout and tied off to create a master point.
When a single piece of equipment is used, a locking carabiner is clipped directly
to the piece. If a sling is used it is generally connected with a locking carabiner
or tied to the piece. |
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MultiPoint Construction
Multi-point anchors are those which connect two or more pieces of protection
together. This provides redundancy should one piece be weaker than the other(s);
if part of the anchor fails there are one or more backups. If the anchor is constructed
correctly, loads are distributed between its parts and the force applied to any
one piece will be only a part of the total force applied to the system.
When to use multi-point anchors
Multi-point anchors are used in all types of guiding situations when:
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Massive natural features are not available.
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Loads are moderate to high (greater than body weight, lead falls, shock loads,
rescue).
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When falls (as opposed to slips) are possible.
Independent construction
By using individual slings or by tying off a single long sling to make a master
point, pieces in the anchor are joined independently. Independent construction
minimizes potential shock loads and maximizes redundancy.
When to use independent construction
This system is the standard technique for creating a multi-point anchor. It
is used when:
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One part of the anchor is (or may be) weaker than the other(s).
• Strength of pieces in the anchor is not easily or accurately
assessed.
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Loads will be relatively high (> body weight).
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Direction of force is reasonably predictable.
• Shock load potential is great.
Series construction
When pieces are in a vertical orientation a single sling can be used
to connect them. A bight of sling is placed in the top piece and the lower
pieces are joined using clove hitches.
When to use series construction:
• Generally in the same places as the independent.
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When pieces line up vertically.
• Since series uses less sling than independent it works well to conserve
gear.
• This construction can be a little trickier to set up and adjust the load. |
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Self equalizing construction
By using a single long sling, a self equalizing connection can be made. This
connection distributes loads to the placements through a range of directions.
However, if one piece fails, the anchor will be shock loaded as the sling extends.
Shock-load potential can be decreased by tying knots in the slings above the
master point but this also limits the range over which loads are distributed.
When to use self equalizing construction:
This method of creating a multi-point anchor is an alternative to independent
construction. It is used in special circumstances when:
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Each part of the anchor is of equal or near-equal strength, that is,
- When each point is strong e.g. near 20kN as in new, CE (UIAA) approved
belay bolts.
- When each point is equally weak and a single, stronger piece will be created
by connecting them with the best possible distribution of loads.
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The anchor will be exposed to forces from varying directions.
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Direction of force is difficult to assess or unpredictable. |
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