double figure 8 question

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Re: double figure 8 question

Postby chh » Mar 26, 2014 6:39 pm

Though the butterfly/single 8 may have it's applications, I don't like it as a general rule. First, I think it looks sloppy. This is an aesthetic thing and totally subjective. Second, as has been said, rig around your rub points....geez! Third, if it's the anchor points and not the rub/cutting points that are the issue, there are much more eloquent ways of load sharing that you may or may not be able to achieve with what you have with you. Um....it depends? It occurs to me that I've added nothing to this discussion.......
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Re: double figure 8 question

Postby PeterFJohnson » Mar 27, 2014 1:46 pm

I guess we are blessed with many rigging options. As chh said, it depends. A double bowline is another option. It has most of the advantages of the double 8 but uses less rope.

A brief defense of the butterfly/8 Y-hang(which is more often a butterfly/butterfly since there is often a traverse line involved):

chh wrote: First, I think it looks sloppy. This is an aesthetic thing and totally subjective.


I can't argue with your sense of aesthetics. I don't find the Butterfly/8 particularly heinous, but I would also note that aesthetics are not my primary concern when rigging so I haven't thought too much about it.

chh wrote:Second, as has been said, rig around your rub points....geez!


I am not sure I understand you here. I often rig around rub points using a butterfly/8 Y-hang. In fact if the information in this thread is correct a butterfly/8 is more effective at this, since it allows you to position the rope anywhere on the plane between your two anchors. Whereas it seems a double eight will slowly equalize until it lies directly between the two points? Granted the more you move the rope towards one anchor with a butterfly/8 the less equal the load sharing. But at least you have the option.

chh wrote:Third, if it's the anchor points and not the rub/cutting points that are the issue, there are much more eloquent ways of load sharing that you may or may not be able to achieve with what you have with you.


There are certainly a variety of ways to rig a load sharing or load equalizing anchor. Eloquence is also a pretty subjective term. But using less rope(than a double eight) and not having to carry any extra stuff for other set ups seems pretty eloquent to me. I don't know of any more eloquent load-sharing anchors personally. I do know of more eloquent load-equalizing anchors. But in most situations I can pre-equalize(or close enough) my butterfly/8 and not have to worry about extension and therefore shock loading that occurs in load equalizing set ups. And since the direction of pull is almost always constant I don't really need an anchor that is dynamically equalizing.

One downside of a butterfly/8 or butterfly/butterfly is that people have to know not to clip into the single strand leg of the rigging since doing so typically places you on just one bolt. Also, as I stated before, double eights are superior to butterfly/butterfly when you need the traverse line that approaches the pitch head to head straight for the knot on your Y-hang rigging. This is often the case if the pitch head is far from walls. I can also think of situations where a fall on a traverse line approaching the y-hang would generate higher shock loads if the rigging was a butterfly/butterfly versus a double eight.

Again, options and it depends. Both ways of rigging are safe and have their place.
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Re: double figure 8 question

Postby Anonymous_Coward » Mar 27, 2014 2:58 pm

:exactly:

Thanks Pete. I had all the same concerns/questions, but I figured I'd let you handle it since you are the butterfly/8 magnate.

I tend to use the butterfly/8 rig when adjusting (equalizing) a double 8 would be difficult for whatever reason. It's also nice when you have already rigged to a single point and then decide to add an anchor.
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Re: double figure 8 question

Postby Tim White » Mar 28, 2014 11:07 am

The butterfly/8 rig works really well when the anchors are far apart. A double Fig. 8 uses much more rope.
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Re: double figure 8 question

Postby bladerunnerevan » Apr 7, 2014 1:45 pm

With a properly tied knot, most likely no. However, on stiff caving rope the chances certainly increase. Also, you need to consider that tying a knot reduces the rope's strength at that point, so if you have enough force for your bolt to fail then the rope may also fail at the knot.
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Re: double figure 8 question

Postby Tim White » Apr 8, 2014 4:20 pm

bladerunnerevan wrote:However, on stiff caving rope the chances certainly increase.

How does using stiff caving rope increase the chance?

bladerunnerevan wrote:...so if you have enough force for your bolt to fail then the rope may also fail at the knot.


Maybe so. But if one is using a correctly tied and dressed knot, one would expect 80 - 85% of the ropes strength to remain. If one was using 11mm rope with a rating of 6,000 MBS, then you are still looking at around 5,000 MBS. Way strong. I'd be more worried about proper bolt/anchor placement/strength and anchor failure. I'm not worried about the knot even if the one of anchors did fail.
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