Primary rigging point

Do you prefer to...

  • Total voters
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Not always a viable option, but when I can I like to get the top out first. Stem sure moves a lot less with all the brush for mass damping. Rarely an option though.
Sometimes I like to take the top off my tie in point also before working the rest of the tree.
 
"Limb it up, top it out, & chunk it down." GB

Applies to most any conifer, but loosely, that progression can be followed on hardwoods as well.
 
For me it's about efficiency. Since I'm at there setting the rigging does it make sense to drop it or can I blow it out easily afterwards when i retrieve my rigging kit. Doing things by rote leaves little to think about. The joy and challenge is figuring out the most efficient way of getting it dismantled.
 
I find when the top stays on there is more of a sway and when its just a spar you can see more wobble and shake. Hope that makes sense.

Another thought is, if you were pruning could you leave that top? If you were ginning remotely would you leave the top?

When it's limbs, tops, smaller blocks I see it the same as using a section during pruning that's to remain, I often do that. But for big wood and fuller logs I was once told to top it first just in case your rigging point ever failed there is less to fail and come to the ground.

Not sure that's a good principle cause I never work in those margins but hey it's what I was told. I usually top and take some lighter blocks out using a top rigging point then I'll set a sling lower down on thicker wood and continue to keep my anchor in the same league. Hope it helps or at leasts keeps you thinking.
 
I usually like to remove the top since you are reducing the load on the stem. As mentioned there are times you might want the vibrations/sway to be dampened, but it seems that overall it's going to have more available strength if you take load off it.
 
To add to that, if the rest of the tree is surrounding, such as a multi trunked big leaf maple or something (we've got a lot of them) I wouldn't worry about it, because it would be too much of a pain to get it out of the middle.

As I picture load happening though, if you were to dynamically side load a spar with a brushy top on it, it's not going to have as much of a bending moment as if it had no top. Because the trunk is stronger vertically then horizontally, it may be sustain a greater dynamic sideload with the top to dampen the sway. It's so variable though to the situation. So much of big rigging in a tree is just an experienced estimate of how much a trunk, branch union, defect, crook in a trunk, etc can handle.
 
Ok question then, say you have a 100' tree (just makes my math easier), say you put your primary rigging point at 80'.

If you leave your top on you can only pull at 80% of the full leverage.
But if you limb and top out a section to use as a primary rigging point still at that same 80' you have now moved your leverage to 100%.

In a straight down rigging scenario this may make 0 difference but if you are grcsing or anything like that it could be something to think about.

Any thoughts on that?
 
I'm thinking that's an oversimplification of the math KevinS. The point load where the rigging is attached is the same technically because it's the distance from the point of reference - the ground. The additional mass above it we act as a dampening mechanism as it's initial movement will be in opposition to the movement of the rigging point, i.e., the top will actually move back from the direction of the rigging point and then oscillate creating the dampening effect. When you're talking that big a load above the rigging point then that oscillation and the potential for failure at a defect along the trunk is increased.

I'm rambling.....
 
No Jontree just tip tie rigging big block from the side.

Not bad points treehumper I was just sharing what I was wondering about thinking about this topic
 
On a straight up and down stem that you are placing your rigging point on leave the brush on top to help dissapate the force generated on the rigging point.(Like tree humper explained) The force has to go somewhere and the force that makes the tree oscillate will actually dampen the force on your rigging gear and the stem. Same thing goes for a tie in point. If your rigging point is located on an angled stem then you might want to take the weight off the end as it could cause your rigging point to fail. This is easly tested, rig a couple with the top on, then pop the top and rig a coulple. You will see much more movement there is when the top is gone. If you are theoretically rigging the exact same size piece with the same rope, at the same angle, blah blah the force will be exactly the same, it will just be dissapated in different ways. Hope that makes sense, I might have confused myself....
 
treehumper said:
I'm thinking that's an oversimplification of the math KevinS. The point load where the rigging is attached is the same technically because it's the distance from the point of reference - the ground. The additional mass above it we act as a dampening mechanism as it's initial movement will be in opposition to the movement of the rigging point, i.e., the top will actually move back from the direction of the rigging point and then oscillate creating the dampening effect. When you're talking that big a load above the rigging point then that oscillation and the potential for failure at a defect along the trunk is increased.

I'm rambling.....
Click to expand...
Treehumper I see what you're saying there. On a total side note I will talk about pulling on a tree now. I you were scalping the tree and leaving that 20' top, so you're tied off 80% of the way up, how much more force (if any) would it take to pull over, compared to if you blew that 20' top out and tied off running the rope from behind the top cut over top to be sure you have 100% of the way up?

Would it be easier because it's at the very top or just because the load is 20% smaller? Again if at all, I often blow out tops if it's windy so there is less effect, but what are your thoughts on that?
 
sherwood7 said:
On a straight up and down stem that you are placing your rigging point on leave the brush on top to help dissapate the force generated on the rigging point.(Like tree humper explained) The force has to go somewhere and the force that makes the tree oscillate will actually dampen the force on your rigging gear and the stem. Same thing goes for a tie in point. If your rigging point is located on an angled stem then you might want to take the weight off the end as it could cause your rigging point to fail. This is easly tested, rig a couple with the top on, then pop the top and rig a coulple. You will see much more movement there is when the top is gone. If you are theoretically rigging the exact same size piece with the same rope, at the same angle, blah blah the force will be exactly the same, it will just be dissapated in different ways. Hope that makes sense, I might have confused myself....
Click to expand...
Nicely illustrated
 
Energy is dissipated through the oscillation of the stem. Damping reduces the number of oscillations that will occur before the system returns to it's resting position. Without the top then there is only the natural damping inherent in the stem, much like a spring. Leaving the top with brush introduces inertia that creates drag at the anchor point. The anchor point (AP) is pulled in the direction of the fall, while the top remains where it was until the force of the pull overcomes the inertia of the top remaining above the AP. Once in motion the top attempts to catch up with the rest of the stem, the wood fibers bringing it back to a neutral position. The amount of the foliage that remains creates the drag that slows the stem, thus absorbing the energy from the falling piece. Here's where letting a piece run affects the force exerted on the AP. This points out two factors in damping: the drag of the remaining crown above the AP and the "modulus of elasticity" of the stem. As the stem reaches it's limit of motion determined by the strength of the wood fibers at the point of the fulcrum, typically at the root plate. However, this energy is transmitted down through the stem causing it to flex along the length, the elasticity of the wood fibers are not the only factor playing into how the tree reacts. As the energy is transmitted through the stem it encounters variances in the woods ability to deform, here's where defects, number of boles, etc..., will effect how the tree responds. In other words it's f'n complicated. In one paper I saw, it's 4th order calculus equation. That's what you're trying to compute in your head up there.

It's a real science to establishing the best place to set your block to balance the top's damping and the excess load it may cause on a defect in the stem above or below the AP. We know from experience that the tree has grown in such a way that when the top is removed we have an underdamped system when we start taking out large pieces (again this is some complicated math to figure this out, yet we're doing this on the fly). To see this in action check out the video of the tree climber in Hong Kong. In that case he was also providing some damping, not much mind you.

Looking at the force that is being applied to the AP remember that it is primarily a function of gravity. That force is a vector force, acting in a direction that is defined in three planes. Think in terms of a graph with a x, y and, z axes. Imagine them as parallel to the stem and then on a plane horizontal or perpendicular to the stem and at right angles to each other. As the piece falls the values along each axis changes as the piece changes its relative position to the anchor point. Now add to that a lean and those numbers become much different and more importantly where there is a top involved it will add to the downward force acting on the stem once it overcomes it's inertia. It will in fact add to the degree of deflection. Again this is all dependent on the balancing of the potential forces acting on a single point. Not just the AP but throughout the stem.

I wish I could find a damn simulation of this. I know one or two exist as I have seen them. It would make this much easier to see. But, I guess my point is, appreciate the complexity of the loading we are placing on the tree as a whole system and that we are attempting to calculate, when we choose our AP, the size of the piece and its relative position to the AP. Add to that whether or not the piece is tip tied or butt tied, the rope is static or dynamic and, whether or not the piece is going to run or not. Oh and let's not forget wind speed, gusts and direction relative to the anticipated fall of a piece.
 
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