TR Anchor with 7mm cord or 1" webbing question


Original Post
Edek Falkowski · · Buffalo, NY · Joined Jan 2016 · Points: 65

I am climbing a bunch in the Adirondacks, and to set up an anchor I need to buy some cordage. Looking to go as cheap as possible for about 100 ft of cord. Static is simply too expensive. Would building an anchor with 1" webbing where each end is tied to a tree, the single strands meet at a figure 8'ed master point be bomber? What knot would you use to tie the webbing around the tree? Would 7mm or 8mm cordalette (same length)  be able to accomplish the same thing?  Would this kind of setup be bomber?

Tayler Mulligan · · Unknown Hometown · Joined Feb 2017 · Points: 0

What type of anchor are you planning on building? 30m of cord should be more than enough to double up with reasonably close anchors. It's worth noting if the trees are far apart you may end up with load amplification on your anchor. An angle > 90 degrees between the 2 legs should absolutely be avoided otherwise the force on each leg will actually be higher than the load on the master point. Otherwise 7mm static cord is rated at ~13kN on a single strand. 13kn is more than enough in a top-rope situation, however the thinness of the cord could result in minor abrasion over an edge/sharp rock causing some major damage. Knot-wise, it will be easier to use the cord, tying around the tree w/ a backed up bowline or a re-threaded figure-8. Climb-spec webbing is rated at 17kN and will be more abrasion resistant than the cord; however tying knots in webbing is more difficult as most knots don't hold well. A rethreaded-overhand, or a water knot, tends to be the go to knot in webbing however it's essential to ensure the tails are sufficiently long (for a TR anchor I would suggest at least 6").

Eric Fjellanger · · Unknown Hometown · Joined May 2008 · Points: 830

It sounds to me like you're overthinking this.

For basic toproping, if the trees are solid, just use one of them. If the trees are not solid, I don't think even equalizing two of them is going to be a very good anchor.

100 feet sounds like a ridiculous amount of cord for a single anchor.

1" webbing around a say a 6" tree, tied correctly with a simple water knot is a standard anchor. There are a lot of other options that you can and should learn about. But a piece of 1" webbing tied around a tree is easy and safe.

Edek Falkowski · · Buffalo, NY · Joined Jan 2016 · Points: 65

For the webbing option, would you tie a closed loop around the tree with a water knot (effectively halving the length of your webbing) or would you tie a water knot so that the loop is just big enough for the tree, then have one end of the webbing loose and the other end heading to the master point? 

Eric Fjellanger · · Unknown Hometown · Joined May 2008 · Points: 830

Definitely the former, I don't think that loading the tail end of a water knot is a safe use of that knot. Just tie a loop and clip to it. Like the example labeled "Single Loop Anchors" at this link:

http://roperescuetraining.com/en/anchors_examples.asp

It would be valid to criticize this setup as not being redundant. If that concerns you, you can use two loops of webbing. Or you could instead buy a cordelette and rig it like this:

http://centralcoastclimbing.blogspot.com/2011/01/anchor-installment-1-trees.html

But most importantly, keep your anchors simple and don't try and invent some new way to use a knot you haven't been taught about.

You should buy and read Freedom of the Hills.

Guideline #1: Don't be a jerk.

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