Quad made from 2 dyneema slings?

Hi all

How safe is it to pre-build a quad from two separate 10mm 4ft dyneema slings? Knots are simple overhand.

Intended use is uneven sports anchors for top roping.

Main concern is knotting dyneema but given there are 4 strands and we are only top roping and using dynamic rope, it should be bomber right?

fyi we currently build quads from 7mm cord but this would be half the weight and bulk. I guess I could just use one strand, essentially a sliding x with limiter knots but this provides extra safety and I was just given these slings and don't really have any other use for them so why not.

Only downside I can see is untying it can be a PITA.

Thoughts?

A single 240 CM sling works perfect for making a quad. With what you have I would clip one to each bolt and then tie them together at the master point equalized to the direction of pull.

BrokenChairs wrote:A single 240 CM sling works perfect for making a quad. With what you have I would clip one to each bolt and then tie them together at the master point equalized to the direction of pull.

I'd prefer self equalising as one of the anchors has three routes leading up to it, a left, right and middle. They are all different grades so when we take the kids, they have the option to doing the easy, medium or hard one without us having to adjust anything.

MHostetler wrote:I've been told to make sure to do at least a figure 8 (as opposed to an overhand) if tying knots in slings. Maybe a figure 9. This apparently reduces the chance of burning the sling when the knot pulls tight

Yep, figure 8 should be possible, might not have enough length to do figure 9's without compromising on the angle.

John Wilder wrote: Well, no anchor system is truly self-equalizing- one bolt is almost always going to take the majority (if not all) of the load. The Quad is fine, a regular cordlette is fine, two draws are fine- totally up to you so long as you're clipped to both bolts.

True. Ok, I'll go the quad but use figure 8's, if only to make untying hopefully that little bit easier.

Actually, can I leave it permanently tied or should I retie it every time we go climbing, maybe to spread the wear points?

John Wilder wrote:The Quad is fine, a regular cordlette is fine, two draws are fine- totally up to you so long as you're clipped to both bolts.

Yeah, this. The forces involved are so low, it doesn't really matter what you do, as long a it's redundant.

A pre-made quad is fine for this, but not required, even for the reason Shane stated. When TR you're generally going to be on the opposite side of the anchor from your climber, and so the force vector will pretty much always be downward, or close to it, depending on where you stand.

I wouldn't stress out over it.

The knots will be easy to untie in dyneema I have used the same knots all day including hanging belays and have never had any trouble untying them after. Nylon slings will give you more trouble. But like said use a figure 8 instead of an overhand. Also I would untie after use since it's so easy to set it up again but that's just me.

Yeah, that'll work. For a TR anchor on a pair of bolts, it is safe enough, too. But why bother with something that complex?

Just setup a simple master-point (over-hand knot) anchor on the two bolts.

You mention having three routes off the anchor as a reason for wanting the "equalization" of the quad. Think about what you're trying to equalize, and what the point of it is. Are you really trying to equalize the load on two bolts because you don't expect either bolt to hold the full force of a TR fall?

If both bolts are good, they'll hold 20Kn or so, and it doesn't matter which takes 100% of the load.

If one is good, and the other is bad -- you only need redundancy. The (nominal) equalization isn't going to matter.

If both are bad, it now becomes a question of how bad. Testing has shown that you don't really get equalization out of a quad, but what you do get is extra extension. This means that if one bolt fails, you're likely going to put more load on the other bolt (increasing the risk of it also failing) with a quad than with a master-point anchor.

Also, since you seem worried about bulk -- a master-point setup is a lot less bulky than a quad setup. So, you can do it with nylon, too. Cheaper, and doesn't degrade as badly when knotted.

I would use fig 8s unless you plan on keeping it tied like that permanently. Especially with skinny slings, overhands will be a PITA to untie. Not any issues safety wise. For TRing it really doesn't matter whether you use 2 draws, tie a power point, use quad, sliding x with limiter knots, etc. Use whatever you like.

As for knotting dyneema, the issue is tying dyneema into a loop (ie knotted slings rather than using sewn slings) because the slippery nature of dyneema causes the tails to pull through the knot under high load. tying a knot in a dyneema sling will reduce the strength but for most applications in climbing this is not an issue.

David Gibbs wrote:YBut why bother with something that complex?

Out if curiosity, what exactly about this do you find complicated?

In order of complexity, I'd actually rank the obvious options like this:

Draws < Quad < Tying a Master Point

Reason being the draws and quad are ready to go (unless the bolts are vertically aligned, but not the situation here). Just clip when you get to the top. The Master Point need's to be tied each time. Draws are simpler because you don't have to tie them to begin with.

This isn't the first time I've heard this argument, so not trying to dig on you. It seems to me a lot of people over-emphasize the "complexity" of a quad anchor.

Brian L. wrote: Out if curiosity, what exactly about this do you find complicated? In order of complexity, I'd actually rank the obvious options like this: Draws < Quad < Tying a Master Point Reason being the draws and quad are ready to go (unless the bolts are vertically aligned, but not the situation here). Just clip when you get to the top. The Master Point need's to be tied each time. Draws are simpler because you don't have to tie them to begin with. This isn't the first time I've heard this argument, so not trying to dig on you. It seems to me a lot of people over-emphasize the "complexity" of a quad anchor.

Unless my eyes are crooked, the picture by OP clearly show uneven bolts and therefore, QD and pre-tied Quad are out of the question.

You're right draws are out, I was just comparing it for complexity. But you can pre tie a quad for uneven bolts. It's "equalizing" nature lets it adjust for some variation, depending on how close the limiting knots are. Especially if you already know how the bolts are configured.

OP is also wanting to prebuild the anchor.

BrokenChairs wrote:The knots will be easy to untie in dyneema I have used the same knots all day including hanging belays and have never had any trouble untying them after. Nylon slings will give you more trouble. But like said use a figure 8 instead of an overhand. Also I would untie after use since it's so easy to set it up again but that's just me.

If knots are that easy to untie after loading, then the knots used to isolate and create redundancy would actually come untied in a cut, meaning you really don't have a redundant system.

I've not heard of that happening, and haven't experienced that myself, but I would look into that if they really are that loose on you after loading them all day...

Brian L. wrote:But you can pre tie a quad for uneven bolts. It's "equalizing" nature lets it adjust for some variation, depending on how close the limiting knots are. Especially if you already know how the bolts are configured. OP is also wanting to prebuild the anchor.

OP seems to concern about untying the knot, so I assume he ties quad based on each anchor. Also, if OP knows the exact bolt angle and distance, then sure, go ahead and do pre-tie a quad. But other than that, you have to tie a quad or MP on the go. In that case, MP is faster than Quad.

It seems to me that OP has concerns about the integrity of knotting in Dyneema rather than which anchor configuration. AFAIK, there is no concern in knotting Dyneema, unless OP is using Dyneema as the rope for top roping.

Pete Spri wrote: If knots are that easy to untie after loading, then the knots used to isolate and create redundancy would actually come untied in a cut, meaning you really don't have a redundant system. I've not heard of that happening, and haven't experienced that myself, but I would look into that if they really are that loose on you after loading them all day...

Highly, highly unlikely. You do know it would have to basically untie itself from like 3 loops after the break for it to give way. You can test this by tying a knot loosely and than try pushing the cord back through the loops as if it has broke and see what I am talking about. I can't say it would be impossible but pretty close to it.

Pete Spri wrote: If knots are that easy to untie after loading, then the knots used to isolate and create redundancy would actually come untied in a cut, meaning you really don't have a redundant system. I've not heard of that happening, and haven't experienced that myself, but I would look into that if they really are that loose on you after loading them all day...

Sorry for the confusion I wasn't saying they were loose just that I have never been able to not get them untied with minimal effort compared to say trying to untie a figure 8 after taking a good whip. However, with the quad you're looking at four cuts needing to take place to cause a failure. One cut even if it slipped through (which I don't find likely considering the forces we're talking about in a TR set up) would still leave you with three points of connection and you would have minimal extension. With the quad being used in a top anchor unless the leader takes a factor 2 the amount of force applied to the anchor is minimal in combination with how slippery dyneema is untying has never been an issue for me though it may be more of a challenge if you did take a factor two directly on the anchor. Hopefully I never actually find out if my assumption is true.

divnamite wrote: AFAIK, there is no concern in knotting Dyneema, unless OP is using Dyneema as the rope for top roping.

Actually there is concern over knotting dyneema. You should only use sewn dyneema and never tie two loose ends together to make a sling. This can fail. Also knotting dyneema does reduce it's strength by about half so that 22kn sling is probably only good to hold around 11kn. Still more than a size 3 C4 so it is not something that concerns me. Sorry if it sounds like I'm contradicting for clarification

Tying knots in a sewn sling of dyneema = reduced strength but still plenty strong and okay to use

Tying dyneema into a sling with knots = death.

dmmclimbing.com/knowledge/k…

BrokenChairs wrote: Actually there is concern over knotting dyneema. You should only use sewn dyneema and never tie two loose ends together to make a sling. This can fail. Also knotting dyneema does reduce it's strength by about half so that 22kn sling is probably only good to hold around 11kn. Still more than a size 3 C4 so it is not something that concerns me. Sorry if it sounds like I'm contradicting for clarification Tying knots in a sewn sling of dyneema = reduced strength but still plenty strong and okay to use Tying dyneema into a sling with knots = death. dmmclimbing.com/knowledge/k…

I wasn't talking about tie loose dyneema together. I don't think OP is talking about that neither. Also, DMM's dyneema series is pure fear mongering. Their tests are all done on static system with no dynamic component.

Shane1234 wrote: fyi we currently build quads from 7mm cord but this would be half the weight and bulk.

If you're doing single pitch sport routes and cragging, bulk and weight should be the least of your worry

ViperScale wrote: Highly, highly unlikely. You do know it would have to basically untie itself from like 3 loops after the break for it to give way. You can test this by tying a knot loosely and than try pushing the cord back through the loops as if it has broke and see what I am talking about. I can't say it would be impossible but pretty close to it.

He just clarified.

BrokenChairs wrote: ... Also knotting dyneema does reduce it's strength by about half so that 22kn sling is probably only good to hold around 11kn. ...

Isn't the quad strength 22kn?

There's 2 slings/4 strands so 22 + 22 = 44kn then the 50% strength loss which brings it back to 22kn?