Remote Retrievable Rigging Solution

[bonner1040]

Something I was toying with today...

<iframe width="560" height="315" src="http://www.youtube.com/embed/tz9fNjSqwdA" frameborder="0" allowfullscreen></iframe>

 

[PCTREE]

Looks like a great system, 2 concerns, not sure if they are valid but I will voice them just for discussion. So 1 you say it has a generous bend radius but I see 2 radius 's first is the generous pulley sheave 2nd is the 1/2 " ring radius. THis concern is only a problem when the loads are high. 2 concern is heat build up on the ring which with a heavy load and long run could be very hot.

As I said not sure if these are issues but might bear some consideration...

 

[bonner1040]

So 1 you say it has a generous bend radius but I see 2 radius 's first is the generous pulley sheave 2nd is the 1/2 " ring radius. THis concern is only a problem when the loads are high.

I was speaking in reference to the span... Even with the ~1/2" ring it is a ~90 degree bend at most, less depending on how it sits. It is my understanding that the hazard with bend radius usually refers to a 180 degree bend. Do i have that right?

2 concern is heat build up on the ring which with a heavy load and long run could be very hot.

Thats a totally valid point...

I should have said that I dont see this as a implement for huge loads/shock loading... If I am in the tree I can easily tie a block with a eye sling that has none of the obvious concerns...But for pruning, static rigging scenarios, lifting situations, and others it seems like it will be a good tool.

Often times we will throw a line into tree B, run a bull line up with a block on it and a work line hanging from it. We then use that line to tip tie and hang tree A while we cut it from the ground. We arent doing this on monster trees, usually stuff in a yard or along a woodline, BUT this technique quadruples the forces on the anchor point, If you were to use the 3RS its only the standard 2X...

Just a couple of thoughts.. thanks for chiming in though Paul I was looking forward to your comments as you are quite the innovator yourself.

 

[FJR]

Like you just said, I much prefer to use a dedicated false crotch line with a spliced eye for a block. I know it is 4x the force, but if you use proper angles it is much quicker to set up. It is really effective when used with the grcs to keep the load as static as possible.

I like the thinking though Nick. I don't see why that wouldnt be ok for light to moderate rigging.

Sent from my Desire HD using Tapatalk 2

 

[CurSedVoyce]

I have set up one like that as well before Nick and only for lighter rigging. I have thought about possibly using a large and small block together in lieu of the ring.

 

[kevin bingham]

I really like a leather tube cambium saver...

 

[SouthSoundTree]

I really like a leather tube cambium saver...

Me, too.


The Static Removable False Crotch is a good technique. 2x's the load, not 4x's. No risk of having the throwline jump off the sheave when pulling up the rope.

Same thoughts on the bend radius created by the 1/2" ring.

SRFC good for high and low loads. For low loads 4x's the load is not a problem.

 

[Jack]

Nice video, Nick ... NICE videographer!!! I tried something similar a while back (not adjustable like yours) ... got a little worried, like Paul & Sean said, about the bend radius of the rigging ring.

 

[bonner1040]

I am not sure its a big concern.. I could be totally off the reso here but isnt a 90 degree bend pretty generous, or does that not make a difference?

 

[rangerdanger]

Sean, wouldn't it be 4x the load since the block is seeing 2x the load already, and a normal static line tied at the base puts 2x the load the on the crotch itself, so 2x2=4. This is correct, right? Just curious, cause that's how I see it.

Cool idea Nick, definitely one to keep in the bag o' tricks.

 

[bonner1040]

Sean, wouldn't it be 4x the load since the block is seeing 2x the load already, and a normal static line tied at the base puts 2x the load the on the crotch itself, so 2x2=4. This is correct, right? Just curious, cause that's how I see it.

Cool idea Nick, definitely one to keep in the bag o' tricks.

Thats how I understand it...

I dont think for a second this is a "be all end all" type of thing... Likely it won't even be kept assembled as I will problly use the block and sling for more traditional applications, but as you said, one for the toolbox.

 

[Marc-Antoine]

I am not sure its a big concern.. I could be totally off the reso here but isnt a 90 degree bend pretty generous, or does that not make a difference?

I was speaking in reference to the span... Even with the ~1/2" ring it is a ~90 degree bend at most, less depending on how it sits. It is my understanding that the hazard with bend radius usually refers to a 180 degree bend. Do i have that right?

The angular bend is not the main concern, but the small radius itself is.
Of course, we could think that the effect is worse with a 180° bent than a 90 or 30°, but theoretically, the rope is stressed the same way under a heavy load : The important point is the ratio between the outer side and the inner side's fibers length at this bend, not the total rope's length involved .

You have the same thing playing in natural crotching if the crotch is uneven or if a small limb is catch under the rope.

 

[bonner1040]

Thats some good info! Thanks for the clarification.

I think as long as the rigging tasks are kept within reasonable limits, considering that and other limitations it would be ok. Yes?

Is there any data on rope strength loss or the potential for failure based on certain radius vs loads?

Honestly my experience is rooted in climbing where bend radius isnt considered at all. Having taken countless big falls on a single biner and rigged mech-adv, and haling loads in the same fashion many times it has taken me a bit of time to wrap my head around the idea.

 

[SouthSoundTree]

Sean, wouldn't it be 4x the load since the block is seeing 2x the load already, and a normal static line tied at the base puts 2x the load the on the crotch itself, so 2x2=4. This is correct, right? Just curious, cause that's how I see it.

Cool idea Nick, definitely one to keep in the bag o' tricks.

Not a "floating anchor" with the block on the end of a rope, which is over a crotch, and trunk anchored.

Static Removable False Crotch is effectively a sling around a limb with a block attached, with a second, non-load bearing, rope attached to the sling in order to set/ retrieve from the ground. In the A&SofPR, a bowline VARIATION is tied at the end of the retrieval rope which is load bearing. Picture from AS thread.


sorry if that's not exactly clear, I'm in a rush, but wanted to check what's new before loading the truck for the guys to take tomorrow while I'm working elsewhere.



Bend radius--think about where the rope is bend the most radically, which in this case is over the ~1/4" thick ring, meaning an 1/8" radius. The fibers of the rope are getting compressed slightly up where they bend around the ring, and at the outer edge of the rope, they are being stretched the most. The outer fibers of a 1/2" rope (ignoring flattening) would be bent around an 1/8" radius plus a 1/2" rope thickness, so the bend/ turn of the outer fibers (most heavily loaded fibers taking more of the strain of the load) would be approx. 5/8" radius (to my way of thinking).

A block sheave that is 5" has a 2.5" bend radius, compared to the 1/2" rigging line giving a significantly less amount of uneven loading of fibers (again, to my way of thinking. There might be some specific detail of this that I'm missing.)

 

[bonner1040]

So once it girths, if you pull down on the red line it comes back?

 

[Marc-Antoine]

Is there any data on rope strength loss or the potential for failure based on certain radius vs loads?

Yes there are, but I don't recall where I found it nor where I store the data. I have to dig a little to find the graph.
Basically, the less the radius is, the less the rope can take a load (or instead, the less a load can be take by the rope).

That's the reason-why the manufacturers impose a minimal pulley's diameter for all the ropes and cables. It isn't mandatory but strongly recommended if you want a nominal strength and a good life time. Careful too, there could be liability issues in case of a failure.

When the pulley's radius is in the range of the recommended radius, the loss is reasonable , like 5 - 10 - 20 %. With our huge safety factor of 7 or 10, we shouldn't worry, but actually, that's false : The safety margin is greatly reduced or even more, canceled out.
For the extreme case, you can look at the strength loss due to the knots, until 50% or more, same phenomenon.
I 'll point out you that the radius on a ring or a biner isn't really far from the radius in a knot (rope bent on itself). So ...

 

[bonner1040]

I 'll point out you that the radius on a ring or a biner isn't really far from the radius in a knot (rope bent on itself). So ...

Is this conversation purely academic then?

 

[SouthSoundTree]

So once it girths, if you pull down on the red line it comes back?

yes.

 

[SouthSoundTree]

Is this conversation purely academic then?

I don't think so.

There is a reason for the industry's prevalance of blocks and marl/ half-hitching and a termination knot in rigging.

 

[Jack]

FWIW: I posted these pix a couple of years ago on another site showing one way of remotely cinching a retrievable block. This is the method Sean diagrammed. It's from The Art and Science of Practical Rigging (pp 100,101 - Donzelli & Lilly, 2001). There's a simpler method, using less rope. I'll post it and more pix, if there's interest.

 

[CurSedVoyce]

Excellent pics Jack

 

[SouthSoundTree]

Ya Great pics Jack. A detail pic on the bowline variation, as in the ASofPR, is useful, if you feel like posting it.

I'm interested to see the 'less rope' version.

 

[Jack]

Here's some close-ups of the bowline. It's a simply a bowline sorta tied 'sideways' -- sometimes called and Eskimo Bowline. And I've added a Yosemite Tie-off. So, I've been calling it an EBY. The first pic shows it tied & dressed but not set. The next two show it TD&S, front and back.

I've got some HFH work to do today I'll post the other 'less-rope-version' when I get back.

 

[flushcut]

Good thread! I am kind of partial to a block on a tag line.

 

[Jack]

Ok ... here's yet another way of remotely cinching a retrievable block. A rigging sling is used for the cinch and a throwline is used to set & retrieve. As I said before, these pix are a couple of years old. So, I currently use a q-link instead of the 'biner (shown), AND CMI RP122 instead of the RP106 (shown). I prefer this technique for a remote rigging redirect. For the main load block; prefer a loopie/block or a tag-line/block, depending on conditions.