swinging some white oak limbs

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Now I remember what it felt like when I learned Santa Claus is not real.
SZ

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WTF he's not real????????????????????????
 
...and none of this crap really matters at all if you have a skilled groundie who knows how minimize stress on the system.



And we've discussed this before, the difference between natural crotch rigging and block rigging is added friction... it's the ONLY difference, everything else works the same. The more tree bark the rope runs over, the less force required to suspend the load on the running end, but the force on the working end isn't reduced.

The load on the tree is the same, friction doesn't make mass go away, it makes energy go away.

If you hold the load static with a natural crotch, the working end of the rope bears the weight of the piece (1x). If the running end goes clear the the porty without touching the tree, it will also bear about 1x... that's 2x total AT the natural crotch.

It's not hard to model this stuff mathematically as long as it's static... but once you put it in motion it's too hard to measure the variables to make a practical model that tree guys could use.

It's ALL about the roper and how skilled they are at minimizing forces throughout system as the piece moves. Humans are better at calculating stuff like that instinctively through experience than any computer.

The visible rope damage to cambium from heat and pressure is OBVIOUS. Run some big pieces through a natural crotch and you will kill the tissue underneath, no way it survives 300-600 degrees of concentrated, high volume heat... you'd do less damage with a blowtorch. I watched a rigging rope burn completely through my PI lanyard in about a second while lowering a 200# piece... that's serious heat... and stupidity, but that's a different thread.
 
Blinky, I'm NOT at all suggesting that NCing a rope if not bad on the tree the rigged piece is of sufficient size. The alder tops that we caught the other day burned right through the bark, and smoked a good groove into the wood.

There was a storm rolling in, and I didn't feel like taking the time to set up false crotch rigging. It was a removal, so didn't matter how much impact I was having in the tree.

Like spikes, I use natural crotch rigging only on non-preservation parts of trees (be it only small sections of a keeper tree that are being removed from storm damage, or full on removals.

Running NC ropes damages trees. If you are setting a NC'ed rope that is meant to be stationary (floating anchor), and it stretches under significant loading, it can move quickly and possibly damage the crotch without knowing it (if it is remotely set from the ground, and the crotch is not being inspected).

This is where a tube cambium saver could be considered for tree protection, while still benefiting from the ease of shooting the line in for the floating anchor (being aware of the multiplying effect of a floating anchor).



What do you think about the F3's of the two scenarios using the POW at the base with a block redirecting up top, and the case of the POW up top?
Each case will have good cushioning from letting it run. The redirected system will have more length of rope with more rope stretch.
 
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I'd rather reduce the load at the rigging point by using a block or rigging false crotch. Moving the friction, and load, down to the lowering device at the base of the tree makes for smoother lowers and less impact on the rigging point.

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This part about "smoother lowers" is important.

I think that a big part of natural crotch rigging is that it is harder to cushion the dynamic load, which is what reduces the peak force/ impact force.

If a person has the skills to accurately judge and execute the effective trunk wrap, it is much different that when people "lock it up" from too much friction (be it NC or POW friction wraps).
 
No way Chip,
The static force on the tree in NC is 2x load-friction, with a block its 2x load. There is a difference.

Bad analogy: a running rope damaging cordage and damaging the tree. The tree is alive and may have ways of surviving that the rope doesn't. All I have asked for is some science to back up these claims.. No one has come up with any yet.

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The load on the tree is the same, friction doesn't make mass go away, it makes energy go away.

If you hold the load static with a natural crotch, the working end of the rope bears the weight of the piece (1x). If the running end goes clear the the porty without touching the tree, it will also bear about 1x... that's 2x total AT the natural crotch.

It's not hard to model this stuff mathematically as long as it's static... The visible rope damage to cambium from heat and pressure is OBVIOUS. Run some big pieces through a natural crotch and you will kill the tissue underneath, no way it survives 300-600 degrees of concentrated, high volume heat... you'd do less damage with a blowtorch. I watched a rigging rope burn completely through my PI lanyard in about a second while lowering a 200# piece... that's serious heat... and stupidity, but that's a different thread.

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The tree becomes a heat sink in NC rigging. Sure, bark and wood are good insulators...compared to???

If anyone thinks that there isn't going to be some damage to trees from friction then they need to use their hands as friction breaks, not any metal device or trunk wraps. EXACTLY how much damage will have to wait for some up and coming undergrad to study on their way to a MS. There are plenty of accepted facts that haven't been scientifically studied to the N-th degree...it is NOT a huge jump here to consider that there is some damage to the tissue. How much? Fund the research and find out.
 
Explain the way in which static friction reduces the force on a component, or tree in this case. In a static system, the static friction, locking the porty etc etc, is what prevents the load from moving. When the load moves, it becomes kinetic friction.

Try picking a load and lifting it in either system, on which system do you exert more energy to lift? Clearly the system with greater friction. If a lifting procedure has more energy exerted of the system, it would follow that a lowering procedure would as well. Newton's action/reaction law.

My point is that in your examples, there is no good argument to subtract the force of friction from the force exerted on the tree.

I watched a vid of you talk a homeowner out of removing a large limb off of a silver maple, because you said it would expedite the mortality spiral. Can you understand that rope damage in tops or other parts of the tree that are thin-barked could cause the same effect?
 
When the load moves, it becomes kinetic friction. It is possible kinetic friction is greater than static friction, therefore when the load is moving there is GREATER friction on the system.





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Static friction is generally thought of to be greater than kinetic friction. Its usually harder to start something moving, than keep it moving, though I was researching a bit and saw that in cases of adhesion (one thing wanting to "stick" to another) there can be greater dynamic friction than static friction (measured by the Co-efficient of Friction).



I believe that the difference between static and dynamic Co-efficients of Friction is negligible as compared to the Co-efficient of Friction between the components of the arborist's block versus the COF of the bark/ wood.


The block works at probably pretty much the same COF whether wet or dry. The bark/ cambium/ sapwood moisture, as well as rain or snow moisture, can lubricate (or maybe it sticks, probably dependent in part on sappiness of the species).
This is one more factor that makes it more difficult to judge and achieve the appropriate amount of friction to effectively cushion your dynamic load.




We've discussed the Belay Tube before in the OLDS thread. This device utilizes the friction of deformation (not the right name...might be stress friction, but I don't remember). The Belay tube bends and straightens the rope significantly as compared to a round device (POW, bollard). I hadn't heard of this type of friction before reading about the BT, then saw some more info on it. Just thought it might be of interest.

I don't know if this additional friction is significantly different than using a POW/ LD anchored in the tree top without a redirect.
 
You're right, I got static/kinetic friction wrong.

The question remains in my mind, however. Does greater friction equal greater force on the system, in this case the tree?

On the running end, the friction reduces the load, for sure. But on the tree, wouldn't the loading be proportional to the amount of friction?
 
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Try picking a load and lifting it in either system, on which system do you exert more energy to lift? Clearly the system with greater friction. If a lifting procedure has more energy exerted of the system, it would follow that a lowering procedure would as well. Newton's action/reaction law.



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Dylan, I believe that the two systems are different in a way that this does not follow.

In the lifting scenario, let's clarify that the rope legs run 180 degrees to one another, and our super spiffy block is so close to zero friction that we'll be aware of it playing into reality, but skip it for calculations. Let's say that friction accounts for about a 20-25 pounds worth of resistance when natural crotched and redirected to a GRCS.

In order to lift a limb that is one hundred pounds with a block which is rigged to a GRCS, you would end up basically needing to pull with 100 pounds of force. 100 pounds of force on the rope on one side of the pulley + 100 on the rope on the limb side combine to exert 200 pounds on the block/ block sling/ rigging point on the tree.

When lowering a 100 pound block, friction eats up part of the force of the weight of the limb (weight is specifically the name of the force of gravity acting on an object, not the same as mass.), so you don't have to give 100 pounds of resistance, rather 75-80 pounds of resistance on the rope.
Friction works FOR you in this instance.

When you are winching, you will need to apply about 125 pounds of force on the rope to overcome friction and raise the 100 pound limb.
Friction works AGAINST you in this instance.

Do you agree?
 
Dylan, What do you think of the scenario's that I "Painted" in the attachment, specifically tree three (friction based at the high rigging point, not redirected)?
 
Regarding tree three,

I think that if we are considering the literal ,rigging point, the resistance force of the hand on the rope (whether natural crotched for friction, or with a lowering device) does add more force to the rigging point than the load itself. If you have to add 10 pounds of force to resist the load, then it would be around 110 pounds on the rigging block and sling.

However, it is my belief that this force is different that the force which acts on the stem as a whole (say you might have a weak crotch/ cavity below). The actual force on the block and sling and wood to which it is attached is a bit higher than the weight of the load, but barring a rigging point failure, the effective stress on the overall trunk is lowest in this scenario WHEN THE DYNAMIC LOAD IS WELL CUSHIONED BY A SKILLED ROPER.


I'll probably have to Paint what I mean, when I get some time. Heading out of town in a bit.
 
I mean to say that in the case of lifting without a block, more energy is required to lift than with a block. This would seem to indicate that more force is exerted on the tree in the lifting scenario. If this is correct, then would it not follow that in the lowering scenario that there would be more energy transfer to the tree due to friction, than with the block?
 
I remember Pete Donzelli talking about 'peak dynamic loads'. this is the shock load on a rigging or climbing system. PDLs don't increase arithmatically, they're geometric so the actual load on the tree gets attention-getting-serious very quickly. Static loads are pretty linear though. It isn't unusual to generate triple loads on rigging points.
 
(I wanted to mention before that friction is a function of force, not movement, more specifically a reaction force against movement. There is friction without movement.)


Think of tree three ...

POW in tree. No redirection of rope.
Load is 100 pounds (this is measurement of the force of the acceleration due to gravity, noted F1). If the resisting force of friction around the POW is 100 pounds the load stays still. The force on the rigging sling for the POW, and the tree at the rigging point is 100. Friction works for us.

Tree 2, re-direction from load to POW via frictiony natural crotch.
Some of the 100 pound load F1 is eaten up by friction, and the POW has to provide the balance of the frictional resistance F2. If the crotch friction (180 degree trunk wrap) is 20 pounds of force, the POW must have 80 pounds of resistance force. 100 + 80 equals 180 F3. The redirection ups the force in this scenario, but friction does some of the resisting, but I believe that this friction doesn't add to the force on the rigging redirection point. Friction is spread between the two points, but the NC friction doesn't apply a force to the rope.


Tree 1, POW and zero friction theoretical block redirection. You need 100 pounds of force at the POW transmitted to the block via the rope in order to hold the 100 pounds of wood. All the friction is concentrated at the (more easily predictable) POW. 200 pounds of force at the block/ sling/ trunk at sling point.
 
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I remember Pete Donzelli talking about 'peak dynamic loads'. this is the shock load on a rigging or climbing system. PDLs don't increase arithmatically, they're geometric so the actual load on the tree gets attention-getting-serious very quickly. Static loads are pretty linear though. It isn't unusual to generate triple loads on rigging points.

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PDL are probably having to do with a negative acceleration (slowing down of piece, deceleration), squared.

A super fast deceleration, especially a lock-up has really high forces. It can be surprising how quickly force builds even with a good catch.

This is why I keep focusing on the importance of Effective Deceleration of Loads, (which is harder to predict with NC rigging).

Its hard to figure on the effects of elasticity of the rigging lines.

Something that I think is important to mention is that the shock absorbing ability of rope is related to how well the force can transfer over the rope, and the amount of rope in the system. A block allows better transfer of force than a NC. Now that there are Polydyne-type rigging ropes (more elastic), that has to be figured in the equations (theoretical and metaphorical).


I think that The Art And Science of Practical Rigging might have a good chart of test loads, but it could have been somewhere else that I was reading about it. My copy is out on loan, so I can't reference it.
 
"Friction is spread between the two points, but the NC friction doesn't apply a force to the rope."

Where is the force applied? Part of the load is eaten up by friction, you say, but where does this go? Is it converted and released as heat? If what you say is true, then it would follow that in lowering situations, less force is exerted on the tree in a system with greater kinetic friction than (ie NC rigging) than one with lesser kinetic friction (ie Block).

"(I wanted to mention before that friction is a function of force, not movement, more specifically a reaction force against movement. There is friction without movement.)"

I disagree here. Friction IS a force which resists movement, not a function of force. Without movement, or in the case of static friction, the resistance to movement, there is no friction. It might be more appropriate to say that friction is a force which functions as a resistance to movement.

Or are we talking apples and oranges here?

I'm trying to figure out which system exerts greater force on the tree. In a lifting scenario, it seems fairly obvious that the NC system would require greater energy to raise the load, and thus exert more force on the redirection point.

Now is it an inverse relationship when lowering with a NC system? For the sake of clarity lets forget about the peak dynamic load, and imagine that we've already caught the load. As we lower the load, the friction between the rope to the tree acts to reduce the load on the running end of the rope. But the force of friction is increased as compared to a block. My question is; does this increased friction act to exert a greater force on that redirect than with a block? Or because the load on the running end is reduced does that mean that the overall force is reduced?
 
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