swinging some white oak limbs

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Nice work, lots of fun when you have a high tie point set in another tree. And good use of the adjustable rigging point set on a tightline, or on second view, tied at the ends of two separate tied off lines. Of course that meant a heck of a lot of side forces were applied on the anchor points. I assume you worked out the forces?
 
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  • #5
I was actually surprised at how little effect the side loading had on the trees used for overhead anchor points. First of all they were eastern white oaks, which are nearly indestructable.. secondly shock loading was almost zero.. thirdly the set up of the anchor points adjusted the vector forces to maximise strength. One side was run through a double crotch to a block, the other side was natural crotch rigged through a backleaning lead, so the lean of the lead moved the vector forces more in line with the grain, as opposed to side loading. Again the video is a great tool to review the results. At 4:00 you can clearly see a large top coming off on screen right, while the natural crotch anchor point is on screen left. The anchor point barely moves. It looks like a gentle breeze might have blown through the top..

rbtree said:
Nice work, lots of fun when you have a high tie point set in another tree. And good use of the adjustable rigging point set on a tightline, or on second view, tied at the ends of two separate tied off lines. Of course that meant a heck of a lot of side forces were applied on the anchor points. I assume you worked out the forces?
Click to expand...
 
Curious as to why you didn't rig off the trees you were in? was there enuff room to do it? that would have been less stressful to the rigging tree, yes?
 
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  • #7
Good question.. lots of answers.. trees were at top of steep hill going down to top of 5' retaining wall... could have been difficult for ground crew to handle such large bits, and could have gotten ugly if tips got hung up on all the surrrounding trees and butts ended up going the wrong way . Also lowering off same tree would have created more shock loads and chances for pieces to swing back at climber. Couldn't back chipper up any further cause of drop off of grade & shorthanded on the ground, making it much easier to drop everything in LZ right behind chipper. and of course NO RAKING!!!
 
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  • #9
No,
BUT those pieces were close to the SWL of the line in a static situation. NO room for allowing shock loads.. The pendulum effect minimises shock loads, especially when pieces are tied off near balance point.. Lowering 40'+ pieces off the tree itself would have either created a situation where they were butt tied, and therefore coming down hard into the rigging, or require the ground man to let the pieces run to prevent them from swinging back at climber.. Could have been done, but would require a lot more care, and still left the groundies struggling with large bits on steep grade.. That said, I sould have put a butt line on a couple of those pieces to slow the swing down, even though damage to surrounding trees was very minimal...
 
a butt line would have been sweet, the long swings back and forth probably did stress the rigging tree more than it showed outwardly ;)
 
How did you set the ropes in the rigging tree, from the ground?
 
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  • #13
It wasn't the force on the overhead anchor points that was a concern. It was scuffing up the bark as the pieces swung into the rigging. Happened once on the first tree and there was a close call on the second tree with that first wood cut. We adjusted the placement of the skyline block for the second cut there.

Both lowering lines were originally set from the ground natural crotched. I ended up climbing the one tree to switch up to a block on a double crotched floating line, which worked well. The second line was left natural crotch.
 
canadiantreeman said:
I agree, Cary. Pendulum swings act with the greatest force when plumb to the ancor. Not a shock load, but still a great deal of force when added to the mechanical force of the block. A sliding tagline would have been ideal.
Click to expand...

Can you elaborate. Seems like the force would be greatest when acting perpendicular to the anchor tree. What do you mean by sliding tagline?
 
If the load was static, then you are correct. But the load swings and when it is plumb to the overhead anchor it is moving at the greatest speed and acting with the greatest force. This means that when the limbs crash into the trees they are crashing with a multiplied force which correlates to the mass of the limbs. In the video they were slowed by incidental limbs and balancing the piece out seemed to shift the mass and help reduce force. More accurately it shifts the mass of the load so the load loses some of its momentum and by it some of the force of the swing seems to be tranferred into the shifting of the mass. It would be really interesting to have had scales attached to the anchors to see how that set up acts. If it were a clean dz and the rigged limbs were free of any incidental contact, like a classic pendulum swing...(and in a perfect world the blocks had scales on them), we would see that the weight of the limbs acting on the block would nearly double when they swing plumb to the rigging...and as the piece swings away from plumb, the force is reduced. My point is in this dynamic scenario the force of the piece acting on the block as it is cut is reduced by the action of the swing.

A sliding tagline is simply a biner or pulley attached to a tagline placed above the work on a rigging line. The biner or pulley 'slides' on the rope as the work swings towards the overhead anchor. This can act to slow down the swing and allow one to retrieve the rigging line sans groundman.

You'll have to forgive me if I'm wrong and it wouldn't be the first time, but I've been laying out watching the Working Climber series for a couple of days and my minds adrift with rigging scenarios at the moment.
 
I see what you mean. I think that I was thinking of max sideloading force, and you're explaining about force on the block, if I gathered correctly.



In rock climbing, the danger of a pendulum swing is avoided as much as possible. I have heard it said, with no verification, that if a climber were to have a pendulum swing from 30' sideways into a corner, the climber would have similar energy to absorb as dropping 30' onto the ground.

IF this is true, then THEORETICALLY and IGNORING energy transfer into rotation, and brush contacting things, etc, then dropping it into the other trees from the side would be like dropping from an equal height to the ground. Of course, a lot will have to do with how the one contacts the other, glancing or direct hit, etc. If a piece is rotating, it has additional momentum if it is rotating toward the rigging tree, increasing the impact, and likewise, if it is rotating way from the tree, it will decrease the impact force.


This impact on the tree climber will also be similar if they take a pendulum swing into a part of the tree.
 
it could all be avoided by climbing higher in the tree to be removed and taking smaller pieces as you work down the stem, no harm to other trees, lawn, house, nada, nuthin' ZIP :) At least that is what I would have done, but what do I know ;)
 
A lot of times I plan on rigging something out. Most of the times it's just quicker for me to climb out to the tips and dice her up.

But I'm young and in shape. :D

I'm sure that'll spark Murph on his "your young, you don't know anything" crusade he throws at SST all the time.
 
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