Extended toprope anchor with single-stranded cordelette

I've been experimenting with using cordelette in a single strand with figure-eights on each end (as opposed to the classic double-fisherman loop). This is inspired by some recent experiences setting toprope anchors at Joshua Tree where placements are often set far back from the face and the master point needs to be extended quite far, sometimes exceeding the capabilities of my 30ft looped cordelette (a long static line would have been ideal, but I don't own one). This previous thread has some examples: https://www.mountainproject.com/forum/topic/109830508/cordelette-as-a-single-strand 

The consensus seems to be it is generally more flexible, and you can still do any setup you normally would with a looped cordelette. However, I'm concerned if the single-stranded legs of the anchor are strong enough. With standard 7mm 12kn accessory cord, the ~50% strength reduction from knotting results in 6kn anchor legs. Probably ok for toproping, but not "unquestionably strong" territory, especially if there is any chance of high fall-factors. Here are two example setups.

Anchor #1: Single strands to pieces 1 and 2, and a double strand to piece 3, with an overhand masterpoint

Anchor #2: Just two single strands, with a BHK masterpoint. Let's assume each piece is bomber enough to warrant a two-piece anchor, but it is necessary to get maximum extension so we can't just double up the cord. Since equalization is rarely perfect, I'm hesitant to trust this anchor for forces exceeding 6kn. Is my thinking correct?

For what uses would you trust one or both of these anchors, and why or why not?

I agree and generally assume 50% reduction for knots. For TR you have the climber and belayer weighting the anchor. With a tight belay it's hard to generate much more force, but any shock load is going to put you near your breaking loads. If you have any sharp edges, or degraded cord from rubbing, this is going to lower that limit as well. I wouldn't be psyched about either of these. Climbing is a choice, not a necessity. I would buy some static or find a friend with some. For my personal safety margins and hazard assessment, this is a poor idea with easy remedies available. 

I'd trust it for top roping if and only if the cord wasn't rubbing against the rock. The single strands are strong enough, but could abrade quickly on those sharp crystals. I'd be inclined to buy a static rope for top roping at JT. 

A Dyneema-cored rope with spliced eyes in the ends would be perfect for scenarios like these, since the splice retains about 90% of the ropes' strength.

What factor of falls are you planning on taking on these anchors?  Are you at the anchor or belaying from the ground?  

In a multi-pitch application, I wouldn’t be that bothered by by either version if I could keep an eye on things.

I'm most worried about abrasion. Get a static rope, pad the edges, or both. 

You can get more length out of the cord if you really want to. Unorthodox, but you can use a v-clove and have the one tail of the cord either exit the focal point knot or bring it down to equalize with the focal point made from the other two legs. 

https://www.alpinesavvy.com/blog/learn-the-v-clove-anchor

Caleb: I am mostly curious about general use, and not a specific instance. I’d be hesitant to take a lead fall on either of these anchors, but perhaps I’m being overly cautious?

Adam: I am aware of the V-clove, though if you’re willing to do that then I think anchor #1 is functionally the same strength and preferable in terms of not requiring two pieces to be close enough together to clove

I understand the abrasion concerns, though those are equally present for the double-stranded anchor legs as the single-stranded. In any abrasive situation padding and/or a beefier material would be much preferred

Get a static.  Or use two cordelletes.  Preferably a static.  With it you can make an unquestionably strong anchor about a million different ways.  You won't be locked in to a single solution.  You can beat the bjesus out of it.

Julian Rwrote:

Caleb: I am mostly curious about general use, and not a specific instance. I’d be hesitant to take a lead fall on either of these anchors, but perhaps I’m being overly cautious?

Okay, that’s why I was asking about fall factor.  I think as you approach factor 2 falls, a 10kn anchor could break.  But if you have gear that holds, the anchor is typically not absorbing the force of the fall.  For most applications, a multi-pitch anchor sees load from the follower, but not from the leader (unless in a high fall factor or with a much lighter belayer).  I’m sure there are applications where this would be a mistake, but standard practice is unlikely to apply the forces necessary for these anchors to reach failure.

I have seen no data that says breaking strength of a figure 8 on a bite is 50%. It is more like 80%. Also 7mm cord can very 9-15 Kn. So look at the brands for stronger single strand legs. Or just buy 8mm at 18Kn.

get some tec cord that’s rated for 19 killer newtons.
Or use static if you’re just TRing single pitch. 

Many folks have recommended buying static rope. Also look in to the "Joshua Tree Toprope Anchor" 

It will allow you to make robust and abrasion resistant toprope anchors. AND you wont have to mess around with a welded knot at the end of your session

Nice use of the couch frame. Mountain Tools in California makes a Webolette which is nice because you get sewn loops at the ends. They would probably make you one amy length you wanted. 

I'd bet the top 3pc would test out at close to 20kn and the bottom would be 10+kn

Thanks all. Again, I am aware a static rope would be ideal. I was just curious if, assuming abrasion were properly handled, you would trust knotted single stranded anchor legs made from 12kn accessory cord. It seems the general consensus is "eh, maybe, but rather just buy the proper materials"

Rick: Interesting point. I have taken the 50% reduction as a general rule of thumb but I imagine it does vary by material and knot type. I looked into it further, and Edelrid has done some tests of the strength reduction effect of knots: https://edelrid.com/int-en/knowledge/knowledge-base/strength-reduction-of-textile-materials-by-knots The page is in English, but the key tables are in German. If I'm reading it correctly, in Table 2, the result in row "Polyamide Reepschnur", column "Achter Anseillbelastung" shows the reduction from pulling a figure-eight on a bight on 6mm 12kn accessory cord, for which they find a 41% reduction in strength, with new material. Assuming a safety margin for less-than-brand-new cord, I'm happy enough with the 50% approximation, though maybe I'm reading the table wrong

Ben Zartmanwrote:

A Dyneema-cored rope with spliced eyes in the ends would be perfect for scenarios like these, since the splice retains about 90% of the ropes' strength.

Whether or not there is a knot at the gear end of the single strand, there IS a knot at the other end of the single strand at the masterpoint.  As such, we would expect a similar strength reduction in the single leg, regardless of whether or not one is used in making the rabbit ear.

Furthermore, dyneema (and other highly static materials) lose more strength in knots (due to their lack of stretch) than materials like nylon, which means that the strength impact of the knot(s) is worse, not better, if this anchor was to be made with a hyperstatic material.

You can't approach 6kn top roping. Even two fattiest fatties, climber and belayer, will together barely generate 3kn (600 lbs).

With rope stretch you barely produce much over body weight even in a relatively nasty fall from an inattentive belayer. The large amount of rope in the system compared to the fall distance assures this assuming you are not top roping on static line.

If you are really worried about this get some Edelrid Rap Line by the foot from HowNot2. Its 6mm and holds 10kn...80% of that is totally fine (1600lbs!). AND it adds more dynamic force reduction to the system. It's rated as lead cord as a twin rope how can you possibly break it top roping? It's definitely going to be easier on your anchor points too which can be a real worry.

Modern rope stuff cuts, it never, ever, breaks. People break long before any reasonable rope choice does ie 5mm might be pushing it but 6mm is reasonable, imo. And the human body is absorbing shock too. You just can't break 6mm top roping. Change my mind with data and I'll take the mea culpa. 

Spend the angst on mitigating cutting and getting strong anchor points, imo.

Julian R wrote:

I’d hesitantly disagree with your first point there Kyle. Knots reduce strength due to tight bends in the cord, which causes uneven strains within the material. However since in e.g. anchor #2 both “single legs” enter the masterpoint in near parallel, and only make tight bends once they’re double up together inside the knot, I think it’s correct to think of the knot as double stranded. Thus double strength times half strength for the knot gets you roughly back to the material’s original strength (for the masterpoint portion of the system in isolation)

If you're looking at the strength of a single strand, it doesn't become double strength because there’s a different strand near it in the knot.

The construction here is very similar to a knot on a bight, which ample testing has shown has a similar strength reduction to other knots.  The Edelrid page linked above shows this:

Kyle Tarrywrote:

Whether or not there is a knot at the gear end of the single strand, there IS a knot at the other end of the single strand at the masterpoint.  As such, we would expect a similar strength reduction in the single leg, regardless of whether or not one is used in making the rabbit ear.

Furthermore, dyneema (and other highly static materials) lose more strength in knots (due to their lack of stretch) than materials like nylon, which means that the strength impact of the knot(s) is worse, not better, if this anchor was to be made with a hyperstatic material.

I'm not disagreeing with you: knots certainly do weaken a Dyneema rope.  Best case scenario, you have a spliced eye at each end, and you make your over-the edge anchor with two separate strops and no knots at all.  With spliced slings as long as 180cm now, and eye-to-eye ropes in 8 and 12 feet, there's a lot of options for knot elimination, which is the best way to get the most out of any rope.  I like static rope over edges, because there's no bounce to make it saw against the rock

I did a test of my Dyneema-cored anchor extenders, incidentally, and found that one strand going into a BHK slid a little until the knot tightened up, then at 11kN, the dyneema core cut the polyester cover, after which the core, left unscathed, continued to slide around while the cover in and beyond the knot bunched up.  It was both remarkable and unexpected.  The machine ran out of throw before the Dyneema stopped slipping, but it never broke.  A test with a single strand going into girth hitch masterpoint also saw the rope slide around at about 7kN without locking up enough to break, or any cover damage.  So two legs going into a girth hitch masterpoint would equalize if more than 7kN was applied to one, and then you'd have to generate a lot more force to load the hitch up enough to break a strand.

Personally, I think the world need to move on from knotted masterpoints, since they tend to load unevenly, however carefully they're tied.  It's something I'm working on..... 

Ben Zartmanwrote:

Personally, I think the world need to move on from knotted masterpoints, since they tend to load unevenly, however carefully they're tied.  It's something I'm working on..... 

Dynamic anchor materials will share load vastly better and the benefits of quads and cordellettes will approach that of using the climbing rope.