Key Concepts:

1. Demonstrate how to build several single strand  anchors
2. Demonstrate how to construct common double-strand anchors
3. Be able to recite advantages & disadvantages of common simple anchors

Terminology:

1. Bombproof Anchor:  a single anchor that will reliably hold a load of more than 20kN
2. Marginal anchor:  an anchor that will not be reliable 

Anchor System Building Principles

• Keep it simple. Simple is fast. Simple is safe.
• The interior angle of the anchor legs coming into the master carabiner needs to be less than 90 degrees, preferably 30- 45 degrees.
• All anchors should be inspected and safety checked by someone who didn’t build the anchor.
• Anchor systems should be rated to withstand 20kN forces. 

Natural Anchors

Trees

• Make sure trees are living, well-rooted, and rooted in normal soil (not sand or gravel)
• Trees should be vertical.
• Historically, the conservative rule of thumb is to only use trees larger than your helmet (28″ circumference) for bombproof anchors (rigging of just one tree)
• Recent research has shown that some trees (living, well-rooted) with smaller diameter 8-12″ can support 15- 20kN loads (Davis, Dennis. 2005. National tree climbing field guide, Holan, Jan (2004) Guidelines for Rope Access Work, Weber, R. (2010). How to Determine Tree Strength and Build Tree Anchors.)
• If you are using only 1 tree for your entire anchor system, longer inspections are warranted, and the diameter of the tree should be a minimum of 14″ diameter at breast height (Cartaya, Speaect 2019, 8-9)
• Keep your anchor slings on trees low. The higher up you go on the tree, the more the force of leverage will work against you to uproot the anchor.

Tree strength based on wind ratings

John Morton presented research at ITRS 2015 on how rescuers could use wind ratings to estimate the strength of a tree. Note, Morton states in the paper, “It is important to note that wind rating values do not
indicate true breaking strength of a tree. Rather, they show an anchoring force the tree can withstand based on wind forces the tree has already withstood. Therefore, a tree may be considerably stronger than these values suggest.”

Link to complete research paper:  http://itrsonline.org/wordpress/wp-content/uploads/2015/11/Morton-Full-Paper_Wind-ratings-for-trees.pdf

The front side of John Morton’s downloadable field guide.

The backside of John Morton’s downloadable field guide.

Boulders or rock horns:

• Should be the size/weight of a large refrigerator.
• Make sure boulders are well attached or secured to the ground.
• Pad any sharp edges on rocks or boulders.

Artificial Anchors

Nuts & Cams:

• Depending on placement & the rock type, the historical, conservative approach to single point artificial anchor placements have been rated at strengths of 5 – 7kN (Philip Spinelli and David Pylman, Joshua Tree Search & Rescue, ITRS 2009 The Viability of Multi-point Rescue Anchors Employing Removable Artificial Protection)
• To meet the typical requirements of a 20kN strong anchor, 4 artificial protection pieces are recommended  (Philip Spinelli and David Pylman, Joshua Tree Search & Rescue, ITRS 2009 The Viability of Multi-point Rescue Anchors Employing Removable Artificial Protection)

Bolts:

•  Should be tight, without corrosion, in good solid rock.

Simple Anchors

Simple anchors consist of webbing or rope ties around 1 anchor. Two or more simple anchors can be combined to form a multiple anchor system if needed (no bombproof anchors available and need to combine marginal anchors to form a bombproof anchor system).

Single Strand Anchors

Single strand anchors are rope or webbing anchors that consist of only one strand of cordage for the master carabiner connection point. All the single strand anchors shown below will have a minimum breaking strength of 20kN.

Single Loop Webbing Anchor (21.50kN*)

This anchor is typically used as an anchor on large rocks or boulders. Tie a ring bend (water knot) to make a sling out of a length of 1″ tubular webbing. Wrap the webbing around the anchor and pad any sharp edges.

• Simple to tie and safety check. Quick to build.
• This anchor has no redundancy.

Hasty anchor (tension-less anchor)

A great rappel or edge line anchor that is fast to tie and strong. A tensionless anchor is a high-strength anchor and retains the full strength of the rope. Tie a figure 8 on a bight at the end of the anchor line and clip a carabiner to it. Wrap the rope 2-3 times around the tree and then clip the carabiner back to the working end of the rope.

If your anchor is not bombproof and you need a second anchor for security, you can wrap a second tree or post that is inline between your anchor and your focal point where you will be rappelling.

Be sure that there is no slack between the two trees when building a 2 tree wrap anchor system.

• Anchor keeps the full strength of the rope 
• Super simple to tie and safe. Quick to build.
• This anchor has no redundancy.

Bowline Anchor

Figure 8 Retrace

Another great rope anchor, especially if rigging supplies are minimal. Tie a figure 8 on the rope, then wrap the running end of the rope around your anchor, then retrace the end through the figure 8 knot. Leave a 6″ tail.

Girth Hitch

A fast, simple anchor to tie when the situation doesn’t require a lot of strength but cinching around the anchor is needed.

• Easy to tie and untie.
• Quick to build. Quick to safety.
• Cinches around the Anchor.
• This anchor has no redundancy.
• One of the weaker single loop anchors.

Wrap 2 Pull 1(24.51kN)

This was the “go-to” Anchor for SAR for many years because of its strength and some grip-ability. When tied correctly, with the knot facing the focal point, the knot is “protected” from being tensioned, increasing the breaking strength of the anchor.

To tie, wrap 1″ tubular webbing around your anchor tree or post 2 times. Then tie the webbing ends together with a ring bend. Pull 1 strand of the webbing towards the focal point while cinching the knot up against the anchor.

• Anchor retains a high % of the tensile strength. Strongest of the single loop anchors.
• Simple to tie and safe. Quick to build.
• Has some cinching and grip-ability on anchor.
• This anchor has no redundancy.
• Anchor takes longer to tie and is more difficult to tie than a simple webbing loop anchor.

Comparison of single loop anchors

Double Strand Anchors

Basket Anchor (37.65kN*)

A basket anchor is an easy, strong anchor to tie with a loop of webbing or sling. Tie a ring bend (water knot) in a piece of 1″ tubular webbing and wrap the loop around the tree or post. Try to protect the knot by placing it behind the tree away from the load. Clip a carabiner or tri-link into the end of the loops.

• Anchor 37kN strong with 1″ tubular webbing (CMC Rescue, 2013)
• Anchor 45kN strong with Dyneema sling (Feryok, 2015)
• Super simple to tie and safe. Quick to build.
• This anchor can also be constructed from sewn runners, slings, or tied with 1″ tubular webbing.
• This anchor has no redundancy (if one of the legs of the webbing break, the anchor will fail).  
• Be careful that you don’t tri-axial load the carabiner with the webbing.

Redundant Double Loop Anchor (38.77kN*)

Fold the webbing in half, so you have 2 strands to wrap around the tree. Then tie the bight end, and the 2 single strand ends together in ring bend. If one of the strands breaks, we will still have one loop holding the anchor together.

• Anchor 38kN strong (with 1″ tubular webbing)
• This anchor is redundant and is a good choice for sharp anchors (still use rope protection)
• This anchor can NOT be constructed from sewn runners or slings, only use 1″ tubular webbing.
• This anchor takes a little longer to tie than a single loop anchor and is a little more difficult to tie and inspect. Some rescuers/climbers may not be familiar with this anchor.

Redundant Wrap 2, Pull 1 (43.15kN*)

This is a super-strong anchor that is easy to tie and inspect. The knot has redundancy and is also easy to untie because the knot is protected from the load from friction on the tree.

Make sure the knot is facing towards the load so that it is “protected,” meaning friction from the wrap around the tree won’t put the full load on the knot to maintain a high tensile strength.

• Anchor 43kN strong (with 1″ tubular webbing)
• This anchor is redundant and is a good choice for sharp anchors (still use rope protection)
• This anchor can NOT be constructed from sewn runners or slings, only use 1″ tubular webbing.
• This anchor is a little more difficult to tie and inspect. Some rescuers/climbers may not be familiar with this anchor.
• This anchor requires longer lengths of webbing to construct.

Wild Guide Pearl:  Master Knots in Simple Anchors

Should you put a master knot in your simple anchor sling? There are advantages and disadvantages to putting a knot like an overhand or a figure 8 on a bight. Advantages: A master knot would provide REDUNDANCY if applied to a basket hitch anchor. A master knot could help alleviate tri-axial loading on the carabiner. Disadvantages: Difficult to untie the knot after loading Decreases the strength of the webbing A master knot was most likely not needed in the photo to the right. Why? The basket hitch anchor around the tree didn’t have any sharp edges, so redundancy in the sling wasn’t needed. The overall angle of the 2 legs coming into the carabiner was narrow, so there was no cross-loading or tri-axially loading of the carabiner. The rescuer went with an overhand knot, so after loading, this knot will be extremely difficult to untie.

*  All strengths from CMC Rope Rescue Manual 4th edition