Reducing shock loads

[murphy4trees]

This subject has come up in a number of other threads and has now earned its own.
In particular I like Spidy's method of swinging branches across and down into the lowering line. So tell me if I got it right.
Say I Am lowering a 25' horizontal limb with the LL in a crotch (or block) on the trunk. In this situation the natural direction of fall into the line is straight down, which will tend to create shock.
NOTE: Spidy says he likes natural crotches because there is less length of line that has to get pretension to take out the stretch. That makes sense.. The other option when using a block is to use some winch device to pre-stretch the line from the ground.
So rather than dropping the limb straight down into the LL, Spidy likes to cut a triangle hinge leaving more wood on the up or tension side. This hinge is aimed to have the limb swing away and down, say to 7 or 8 o'clock.
I Am guessing he likes to tie the line 1/3-1/2 way out the limb, close to the center of gravity, and leaving it tip heavy. This gives the line enough leverage to "hold the limb up" during its swing and because it is close to the center of gravity, there will be slower movement once limb breaks free.
So as the limb begins to swing, it gradually loads line. This action of swing rather than drop also allows ground support more time to get ready to allow limb to run, if desired. When the limb tears free, it will slam back into the trunk, butt up, so climber needs to get his body above limb/ behind trunk and or have ground support let it run.
Is that about right?
What else do you all do to minimize shock?
God Bless All,
Daniel

 

[jhr]

Dan,

I'm no pro but what we do is pretty much what you had stated about tying half way with a hinge that lowers slowly which tighens the rope. When the limb is free we usually lower from a break with a fluid hand over hand motion, no jerking, the climber really doesn't have to worry about lowering at all, it's up to the ground crew. The only time there is shock to a rope is if we have to drop the limb 3 -5 feet fast to avoid swinging into the climber. and if you lower it right you can have it pretty much in the chipper before it ever hits the ground!!!

 

[TheTreeSpyder]

Hmmmmmm, some adjustment.........

Schedule, that at tearoff the hitch on load is right under support anchor( no pull, neutral), or hitch between you and Overhead Support anchor (will pull away). Now, if length between hinge and hitch on load is longer than between hinge and support anchor, you have to let load angle down before tearoff, till hitch to support anchor pull is neutralized. Notice, that very action can tighten the line! Also, you can be giving so much support to an almost torn off limb (from hinge); that the climber can move back, and groundy starts to slacken the line thereby removing support from load and causing hinge to fold; with climber clear! If hinge and holding wood (leaning towards triangle hinge) are scheduled on a 'doable' path, can fold at 45-80 degrees quite nicely.

Seeing as you are using gravity to set and power the system,and the leverage of the length between hinge and hitch (that becomes ballast for the heavier, softer, farther end at tear off, and gives a lever for lifting the head out of a hang up), we are dealing in some situations where bigger/longer is better, as size and weight are shifted to our side; they werk for us now!

Have been toying in my head on how to express all of this.

i werk with low/no shock, trying to keep the load up as long as possible, before heavy end tilts down, pulling the log end up off the obstacle below. Both of these things are achieved by werking a tight line, that has no play in the machine. Having the motion self tighten the line to the load's prescribed/ needed support; to pivot horizontally (when line is so tight, load can't drop anymore), higher the support, the flatter the travel through that given area.

High, close friction gives less line area that must be stretched by this action, also reduces anchor load; both making for more positive mechanix. Scheduling this up and to the side gives a sidewards pull. A nice widemouth hinge can almost usher qround the load into the rigging 180deg.; and slowly enough to witness the harmony and flow of all these parts you have scheduled from the structure before you that is diffrent each time.

Working triangle, focused hinge in, maybe self tourquing rig; combining them all in one fine tuned machine; ......well it's like one of Rog's pix.............!

 

[TheTreeSpyder]

Here would be self tightening rig application without steering over for simplicity.

The idea is to have total support at tear off of the hinge. This shows the farther you go out; the more automatic pre-stretching you can call on. Now of course going out further, also provides more balanced support (still keeping green end heavy), so you can actually lower the limb further on the hinge with said support-pretightening even more!

i call the hitchpoint a decision, for it is, not just any spot on load, but specific positionings can impart specific and diffrent properties for you to choose from.

Also (IMAO), when the line becomes so tight per weight of the load; it can not stretch anymore; so is like cable (with firm OverHead Support Anchor). At this point the whole machine changes; for instead the pivot point being the hinge it becomes the hinge that is the pivot. Totally diffrent game!

 

[Kneejerk Bombas]

I thought I was confused with the hinge drawings...

If the pulley is above the branch, where does the shock load come from?
Don't you just pull the slack to take the stretch out of the rope? I don't do natural crotch rigging, but with a pulley, we can put the notch on top of the branch and lift it, if needed.
Throw on a balancer and you really have a perfectly shockless system.

 

[TheTreeSpyder]

Pulleys are superior in lifting, for you don't have to fight the friction that only helps in lowering. Doing some of the work and reducing the anchor load; which is reverse in lifting, you fight the friction, and it increases the anchor load.

We pretighten what we can, and let this meter and set the rest automatically, plus as we get into climber controlling load; compression tightening into friction device becomes less likely. You could get away without the step of compression tightening with pulley on this, under the right circumstances; but you have more line for it to prestretch. Anchor load will still be higher without high friction.

i believe with out presetting, hinging down (ie. rope, and snapcut), one could still shock this system, even with direct overhead support. If you play with the pulley and line tension you probably get similar effects at what i'm trying to reach, with more time and equip. i try to get the system to pretighten to the load (without guessing, automatically), with less anchor load.

Pulley and compression pretightening, si superior in some ways, not always necessary. Combining this with aimed, wide swivelling hinge, and yes triangle; puts together a very powerful machine that worx in harmony with it's parts.

P.S. Dang you should see the drawings i scrap trying to get to the easier ones to post/read!!! Perhaps, if i could make a series of drawings for mini movie/slideshow; eventually we should evolve to vid. capability here.

 

[TheTreeSpyder]

Here i try to show how a potentially dangerous setup, can be handled to work for you. Pre-tightening the line as it goes, also how we shedule the hitchpoint of the load to be under the anchor point. When you line up the 2 points at seperation of load, you can eliminate motion after tearoff from hinge, it will hang there peacefully on a prestretched line.

Write now i have been just looking at lowering stuff straight down, offering this concept first, working with these principals. Taking it a step further to pulling around by not having the Overhead support anchor like Daniel points out isn't too far a throw.

 

[TheTreeSpyder]

Try pic again...............

 

[Kneejerk Bombas]

It seems like you are putting huge loads on the hinge unnecessarily. If the pulley is above, there won't be much, if any, shock load. If you load that hinge up with huge forces, it could pop back and injure the climber.

 

[murphy4trees]

MM,
How do you usually rig your spider legs?
How 'bout on the big stuff?
Thanks,
Daniel

 

[Kneejerk Bombas]

On small and medium stuff I just make do with what I have with me. For example, one leg could be made by tieing a butterfly loop about two feet up the bull line from where it's tied to the limb, and the other leg is a strap and carabiner, girth hitched to the limb and clipped to the butterfly loop.
If I know that I will be needing a spider leg, or if it's a bigger limb, I use a real spider leg.

When we do a crane removal, I use the slings the crane operator brings. They have different lengths and are rated for the loads we are creating. Most crane guys don't want to use rigging stuff they are not familiar with, plus this puts the liability back on them, to some extent, if one fails.

 

[TheTreeSpyder]

Good observations Mike.

The trick is to get the line to take the load, to have hinge hand it off to the line, to start with line tight, and have the load gradually tighten it. sometimes this self tightening is so powerful the groundie has to let some slack so limb will tip down. That is ok, it is easier to put more slack in werking system than take it out!

i don't know if pulley above can guarantee no shock loading, seems like a load could still be cut free suddenly on line not totally prepped for it.

On the balancer; i beleive i saw that idea in an arbo publication (NAA?) before the retail model and made my own; then evolved to spyder leg b4 retail on my own journey- but this is where i ended up! Perhaps i didn't play with balancer long enough to fine idts secretss, but even watching ArboMasters do it at a show; i personally (and 2 guys that came with me) thought this alternative (i offer) worked better. Perhaps each is better in its own place and circumstance. High and over gives good support too; but would have to be higher than directly overhead support; as there is only so much support, part of support is used for pulling around when support is not directly overhead. B-B-b-buttttttttt; any part of load's weight moving sideways is not pulling down on hinge and line (at that point)! So these parts are stressed less, at that point.

The real, real magic in this IMAO, is in the machinery 'changing guard'. In all my leverage etc. examples, there are 3 parts: 1-non moving pivot, and 2 moving parts (input and output). In these examples here, the weight of the head pulling down is the input. In normal rigging, the hinge is the pivot, and the line is pulled down as it stretches, as hinge is cut. i try to get the line to stretch all it can for the load (before tearoff); at that point, the hitchpoint on load becomes the pivot, from that point to the hinge becomes a lever for the hinge to control the head thru. The machine has 'rolled over' and become this diffrent machine with these new attributes i have been talking about. That same part (between hitch and hinge) becomes ballast for the green end at tearoff (cuz i leave softer, farther end heavy); also in clearing obstacles that blaast length is free length; in thaat any part above the hitch (on prestretched line) doesn't effect clearance of obstacles, as only length below hitch effect that.

Anyway have gotten very nice sideways sweeps with allthis before tearoff, sometimes with hitch 15' from hinge, branching starting another 5' out, so this limb might sweep across the clock from 10:00 to 3:00 on the hinge, hang horizontally, then be cut free, as the soft head tips down into the safe zone after riding a 20' arc around. Sometimes so smooth and gracefull it looks hydralically dampened.

i have a few more tweaks to add to this and make it more positive in diffrent situations; some which wee have talked of in other discussions. Hitch point, self tourque, coming under load with line, focus angle of hinge, sweating in, triangle hinge etc. Sometimes could seem like a lot, unless ya have these methods on your belt and jsut do'em without a thought!

 

[treeclimber165]

So basically you are saying to tie the limb further out, but still keep the brush end heavy. Then when you cut it, let it hinge around towards the lowering point so the groundman can control the rate of descent and the limb is straight under the lowering block when the cut is complete.

Took me a couple times reading it to figure out where you were going, but I've been doing that for years.

 

[The Big Hurt]

This lloks like good technique....something I would be interested in getting into. I do have a question though...How do you know the limbs point of balance before you use the balancer technique? Do you just estimate the POB with room for error guessing slightly towards the side of the cut leaving the brush side to tilt? And what is the spider leg for?

 

[The Big Hurt]

I tried

I tried to make an illustration in paint to show the question that I ma asking but it is a 694KB file.....7 times the size this sight accepts.....how do you shrink the size of the file down to post it?

 

[TheTreeSpyder]

if you have msoffice installed, it has filters that go into paint and adjust it so you can save .bmp pix as .jpg (smaller) or even .gif (smaller yet).

If not there is a registry tweak somewhere on MS site i beleive.

Or you can try other image editing software you might have.

Didn't think i was the only one on this track, but have named the parts, and am bringing around more tweaks and technique in this to toss around; as i belive it is very powerful!

Mike drew up pix for balancer and spiderleg in his posts on this thread for you.