Rigging knot

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Rigging knot

Postby GroundquestMSA » Mar 18, 2015 10:31 am

What knot would you use if you wanted to tie the midpoint of your rope into an anchor but for some reason couldn't use a tensionless hitch. Say you are tying into a rail or angle iron with small diameter. Also assume that you haven't any other material with which to build an anchor. Would a bowline work ok with such a doubled rope? I don't know what this would be called. Besides a bowline. A carabiner could be added to the tail (which would be in the form of a bight) and clipped to the loop in place of a backup knot? OR Would you just tie a fig.8 bight and clip it to he main with a carabiner?
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Re: Rigging knot

Postby Phil Winkler » Mar 18, 2015 10:42 am

two half hitches. But, a bowline is always my favorite in caving and boating. JV used to be able to tie a bowline with one hand. It was something to see.
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Re: Rigging knot

Postby Scott McCrea » Mar 18, 2015 10:44 am

I've tied clove hitches around trees for mid-line anchors. You can do a tensionless hitch on a bight in the middle of a rope. A bowline-on-a-bight will also work.
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Re: Rigging knot

Postby GroundquestMSA » Mar 18, 2015 10:53 am

Scott McCrea wrote: You can do a tensionless hitch on a bight in the middle of a rope.

Yes, but not on a little bit of angle iron, unless you use soft rope or 470 million wraps.
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Phil Winkler wrote:two half hitches.

This would make a slip-knot right?
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Re: Rigging knot

Postby Scott McCrea » Mar 18, 2015 11:10 am

Tensionless hitch on a bight: two wraps and biner back into the main. Just like on a tree. Diameter of the anchor (angle iron) doesn't really matter. I would pad the angle iron though.
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Re: Rigging knot

Postby GroundquestMSA » Mar 18, 2015 11:13 am

Very well, will experiment.
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Re: Rigging knot

Postby Scott McCrea » Mar 18, 2015 11:25 am

Let me revise a little. If the diameter of the anchor is small, you may be better off with 3-4 wraps so the knot and biner are not stressed and twisted as much. Another consideration with angle iron is the twisting action a tensionless hitch will put on it. TH only pulls from one side. But a bowline on a bight would have an even pull—no twisting.

Ideally, I think, I would pad the angle iron well and use webbing to make a basket hitch. Then biner the rope with a fig8bight.
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Re: Rigging knot

Postby LukeM » Mar 18, 2015 12:16 pm

Yeah, I was going to suggest a short length of webbing and do a basket rigging or wrap 3/pull 2 (or 2/1). Seems to work really well in industrial situations where you don't know what you'll be encountering and you don't need to worry about taking up a ton of rope with a doubled bowline.
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Re: Rigging knot

Postby GroundquestMSA » Mar 18, 2015 2:29 pm

After playing with the tensionless hitch on a bight on 2" square ladder rung (closest I had to the little angle iron I may have to rig from), I guess that it would hold, but it wouldn't be "tensionless". Remove the biner and the wraps slip off immediately, no matter how many there are. Of course, with the carabiner in place, it worked fine, it's just not the tensionless hitch I'm used to; the one that works almost entirely by friction between the anchor and rope.

One of the reasons I'm trying to get by without webbing anchors is that the rigging point will need to be moved often. If I tie water knots for a w3p2, I'll be fighting to untie knots every half hour.... Ah but that's not a problem with a basket hitch is it? I'd forgotten about this and have never used one, thanks for the reminder. Water knot or beer knot for slings?
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Re: Rigging knot

Postby Scott McCrea » Mar 18, 2015 3:21 pm

Water vs. Beer knot: doesn't really matter. Beer may be a little stronger, but the Water is strong enough. Beer is harder to tie, but looks really cool.

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Re: Rigging knot

Postby GroundquestMSA » Mar 18, 2015 3:26 pm

painting
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Re: Rigging knot

Postby Anonymous_Coward » Mar 18, 2015 3:32 pm

GroundquestMSA wrote:What knot would you use if you wanted to tie the midpoint of your rope into an anchor but for some reason couldn't use a tensionless hitch. Say you are tying into a rail or angle iron with small diameter. Also assume that you haven't any other material with which to build an anchor. Would a bowline work ok with such a doubled rope? I don't know what this would be called. Besides a bowline. A carabiner could be added to the tail (which would be in the form of a bight) and clipped to the loop in place of a backup knot? OR Would you just tie a fig.8 bight and clip it to he main with a carabiner?


I use the "doubled rope" bowline quite a bit for this purpose. It works well and is fairly easy to untie after loading.

Instead of a backup knot, use the Yosemite tie off. This will result in a bight of rope sticking out forwards from the knot. This bight can be very useful for clipping into. For example, it makes an excellent place to clip in your cowstail during a "rappel test."

This doubled bowline with the yosemite loop in front is sometimes called a "fat rabbit."

When tying around a small-diameter anchor like an angle iron, I put one wrap in the loop around the anchor. This causes the loop to cinch around the anchor, much as a tensionless or wrap 2 pull 1 does. This can be especially helpful when trying to get your fat rabbit to stay high on a tree or other vertical post.
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Re: Rigging knot

Postby Stridergdm » Mar 19, 2015 9:22 pm

Scott McCrea wrote:Tensionless hitch on a bight: two wraps and biner back into the main. Just like on a tree. Diameter of the anchor (angle iron) doesn't really matter. I would pad the angle iron though.


I can't find the article, but there's a great article out there, complete with the math (so it must be true! :-) describing why to a first approximation the number of wraps is independent of the diameter of the post (basically the smaller the port, the tighter the "angle" formed by the rope so more force is imparted over the smaller surface area).

Obviously things like https://www.youtube.com/watch?v=yVDMkrJUGMs show that's not 100% true, but I don't think number of wraps there is the issue. :-)

And for the record I was taught by someone who did some industrial rescue that a valid rig for an emergency haul out was essentially two wraps around a railing with the one end tied off. The wraps took most of the force.
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Re: Rigging knot

Postby GroundquestMSA » Mar 23, 2015 10:27 am

Stridergdm wrote: the number of wraps is independent of the diameter of the post (basically the smaller the port, the tighter the "angle" formed by the rope so more force is imparted over the smaller surface area).


The good old capstan equation right?

I should correct something I said earlier.

GroundquestMSA wrote:After playing with the tensionless hitch on a bight on 2" square ladder rung (closest I had to the little angle iron I may have to rig from), I guess that it would hold, but it wouldn't be "tensionless". Remove the biner and the wraps slip off immediately, no matter how many there are. Of course, with the carabiner in place, it worked fine, it's just not the tensionless hitch I'm used to; the one that works almost entirely by friction between the anchor and rope.


Even in this setting the biner is not under tension unless the rope is loaded/unloaded repeatedly. However, the carabiner does keep the hitch from failing. I remember Eliah Kagan arguing that the tie-off in a TH was vitally important and kept the hitch from collapsing and failing. While many of us have demonstrated that this is not the case in some settings, such as when wrapping a big rough tree, it is true when wrapping a small diameter, low friction anchor.
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Re: Rigging knot

Postby Stridergdm » Mar 24, 2015 5:22 am

GroundquestMSA wrote:
Stridergdm wrote: the number of wraps is independent of the diameter of the post (basically the smaller the port, the tighter the "angle" formed by the rope so more force is imparted over the smaller surface area).


The good old capstan equation right?

I should correct something I said earlier.

GroundquestMSA wrote:After playing with the tensionless hitch on a bight on 2" square ladder rung (closest I had to the little angle iron I may have to rig from), I guess that it would hold, but it wouldn't be "tensionless". Remove the biner and the wraps slip off immediately, no matter how many there are. Of course, with the carabiner in place, it worked fine, it's just not the tensionless hitch I'm used to; the one that works almost entirely by friction between the anchor and rope.


Even in this setting the biner is not under tension unless the rope is loaded/unloaded repeatedly. However, the carabiner does keep the hitch from failing. I remember Eliah Kagan arguing that the tie-off in a TH was vitally important and kept the hitch from collapsing and failing. While many of us have demonstrated that this is not the case in some settings, such as when wrapping a big rough tree, it is true when wrapping a small diameter, low friction anchor.


Yeah, that sounds about right (the capstan equation).

And yeah, while I've demonstrated a TH will work w/o the carabiner clipped in, I still clip it in in practice because... well things move.
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