swinging some white oak limbs

Im just thinking here so its more a question,

If the rope goes through a pulley with less friction wouldnt more of the weight being dropped be transferred to the anchor point at the bottom of the tree. If you were to have more friction by NC rigging there would be less weight at the base of the tree. Wouldnt that mean more is at the point of friction?
 
any one want to let me do a removal with a set of scales attached to a rigging point. i'll do both; dry crotch and false crotch rigging. another climber in the tree to read the scales between pics. Dry Crotching should provide results like the O.L.D.S. lowing system. in south sounds illustration figure 2 is flawed, it should be: total force= force line 1+ force line 2- force reduction from rope stretch-anchor deflection force line two=force line one-friction at rigging point. to talk about force multiplication via M.A. is to talk about efficiency. the co-efficient of friction while Dry Crotching is at best variable. to explain http://www.mathsrevision.net/alevel/pages.php?page=79 read the links http://www.engineershandbook.com/Tables/frictioncoefficients.htm
the reduction in efficiency will reduce the M.A. that is a mathematical fact. does it reduce the force at the anchor point? well that is another matter entirely. so who wants to pay me to do this study?
 
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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.

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You're asking for science and you don't even understand it. Besides, I'm pretty sure that what I said was, FRICTION IS THE ONLY DIFFERENCE. Friction saves you a bit on the running end while the system is static, but not once it starts running.

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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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What, you want a perfect analogy? OK I looked at a natural crotch we used on a white oak takedown to lower some 100-2--# pieces. That crotch was smoked, no way cambium and delicate meristematic tissue survive 400 degrees... no way. It doesn't take a degree in thermodynamics to figure that out.

You ask for science as though guys have been doing studies on ropes in natural crotches... but I haven't seen one. Maybe you can use that wonderfully innovative mind of yours to do some yourself?

I just love how NOTHING, not one thing you ever do has been an error or mis-judgment... I think that's hysterical, that ANYBODY on this planet can be THAT screwed up. You don't learn Dan, cuz your to busy 'teaching'.
 
I suppose thats what I'm trying to figure out, Jeff. Whether there is indeed a force multiplier with a block that isn't present in the NC system and whether that force exerts greater pressure on the tree than NC rigging. No question which is more efficient, the block wins hands down there. I am not sure I agree that simply placing a block in a tree increases the load due to mechanical force, it seems the same thing as throwing a rope over a limb. The advantage is efficiency. One can create MA without blocks, but more energy needs to be input in the system to provide the same output as with the use of blocks.

Allmark, that is precisely what I'm wondering.

Oh and Jeff, you do the cutting and I'll read the scales!
 
that all depends on how the system is hung in the tree. to reduce ma force multipliers you have to reduce the angles on the blocks or natural crotches and reduce the efficiency. on a single crotch my hypothesis is: the effects of dry crotching to reduce MA will be negligible once the crotch is "burnt in"; where as when double crotching or triple crotching the effects of the lowered efficiency will be more profound and will reduce the load at the anchor points by a notable difference. i wish i had a paint program.
 
MA being mechanical advantage? Its force I'm looking to understand; more specifically whether it is present or different on a NC system when compared to the same system using a block.

Burnt in...you mean the rope wears through the bark to the sapwood right? I understand that the friction may reduce here because the bark is a rougher surface, but the overall force acting on is what I'm after. If you are implying that a 'burnt in' NC union functions as well as a pulley I would have to disagree.
 
MA=mechanical advantage. your missing the point, MA is a force multiplier. to reduce force on the anchor point from a heavy snubbed load involves three things: rope stretch, reduction of MA, and dynamics of the anchor point. the first one we can control buy being a good rigger and selecting the proper rope for the job. the last one..... well, it is what it is with this job, sometimes we get a great anchor point and sometimes it's less than desirable. now the second one is highly manipulatable. to explain i would have to write a three hundred page book on topics that i'm not qualified to train on. my hypothesis is this: there is a force reduction at the anchor point due to the loss of efficiency from friction in the MA system. since energy can nether be created or destroyed then the energy is released as heat onto the crotch of the tree; thus reducing the force of the load on the anchor point and destroying the cambium tissue in the process from force and heat. an example of this principle: the brakes on a car, force of forward momentum transferred into heat, to much friction equals loss in efficiency thus resulting in higher heat at the friction point and eventually a stop in motion once the loss in efficiency is high enough.
 
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my hypothesis is this: there is a force reduction at the anchor point due to the loss of efficiency from friction in the MA system.

since energy can nether be created or destroyed then the energy is released as heat onto the crotch of the tree;
thus reducing the force of the load on the anchor point and destroying the cambium tissue in the process from force and heat.

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Jeff, I might be wrong about all of what I have said, and I am very tired (up til 5am) at the moment. I'll have to reread when I can understand your point(s) about my drawing.

BTW, paint is under Accessories in the start up menu on the PCs that I've used. I didn't purchase it.



I agree with both parts of what you said above. Kinetic energy (energy of motion) is converted to heat energy at the crotch. This same thing also happens at the LD.



I agree that limb (tree) defection is an energy absorber, which is another variable to consider. I am not sure if it changes much or at all between the three situations. (tired)



Dylan, (again, tired) I think that we are in agreement that friction is a force resisting another force.

Friction is present without motion. I think you MIGHT have said otherwise. When we walk, we have a foot stationary relative to the walking surface. In other words, there is no relative movement. There is friction. If our backward force (foot pushing us forward makes a backward force relative to the surface) is greater the the resistive force of friction, then our foot slips as we overcome friction.
 
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Im just thinking here so its more a question,

If the rope goes through a pulley with less friction wouldnt more of the weight being dropped be transferred to the anchor point at the bottom of the tree. If you were to have more friction by NC rigging there would be less weight at the base of the tree. Wouldnt that mean more is at the point of friction?

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Mark, I believe that some of the energy (which as Jeff mentioned to neither be created or destroyed (it only changes form)) is changed from Force to Heat.
 
For starters, I'm glad we're having this discussion...I'm learning a great deal about things I had previously taken for granted. I operate by the rule 'when in doubt, cut smaller,' so I have a greater margin of error in sticky situations. Maybe when I'm the Michael Jordan of tree cutting and too lethargic to climb higher and cut smaller, maybe then I'll start wailing on trees like a category 1 storm.

We're basically talking about a simple pulley system here, for clarity. Either the rope is run overhead through a pulley or through a natural crotch or over a limb.

So, in our examples the force multiplier of either the block or natural crotch is 1, correct? As others have stated before the difference in the lowering operations is the friction. So, it seems we've at least established that there is no extra force from mechanical advantage acting on the union when a block is present as compared to the rope running over a limb or through a crotch. And we all agree that the force of friction transforms a percentage of kinetic energy into heat.

Jeff and Sean both seem to agree that this transformation equals a net reduction of force on the overhead redirect. For me to best understand it, I look at it as an inverse relationship when when compared to lifting. In the case of lowering, the force on the redirect is reduced due to greater friction. In the case of lifting, the force on the redirect would be increased due to greater friction and the need for higher input to overcome this force.

Are we in agreement at this point?

When is motion not present?

And don't get me wrong, in rigging scenarios, the skill of the roper cannot be understated or taken for granted. A smooth run can reduce the dynamic loading considerably. This is why I like self-lowering
grin.gif
 
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Maybe when I'm the Michael Jordan of tree cutting and too lethargic to climb higher and cut smaller, maybe then I'll start wailing on trees like a category 1 storm.

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That's funny, but you should aim higher, I'm thinking you could do Cat IV.

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We're basically talking about a simple pulley system here, for clarity. Either the rope is run overhead through a pulley or through a natural crotch or over a limb.

So, in our examples the force multiplier of either the block or natural crotch is 1, correct?

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We might just being saying it differently but the way I see that is, 2X at the high anchor = 1X on the working end + 1X on the running end (assuming friction is insignificant)




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As others have stated before the difference in the lowering operations is the friction. So, it seems we've at least established that there is no extra force from mechanical advantage acting on the union when a block is present as compared to the rope running over a limb or through a crotch.

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Not from MA but when the system is in motion shock is a potential multiplier depending on how the load decelerates.

This is thing...
When the system is motionless (pretend the piece was snubbed off and is now at rest still off the ground), that's when you have 2X. Once it starts moving (accelerating), the load on the anchor curves down as acceleration goes up. But the load has to decelerate and come to rest at some point and it's the rate of deceleration that determines how much the load will be multiplied and how much additional force from shock the anchor has to absorb. Shock absorption is all about using time to spread out energy.
Motion matters.


Friction at a natural crotch DOES reduce the tension on the running side of the rope, that's why double braids are generally less good for natural crotch rigging, the inner braid slips and goes out of balance with the outer braid. That friction can be good AND bad because while the high anchor has less total force acting on it, the roper now has less control when the system moves. We've all seen trees bob like fishing poles as the groundie feeds some rope, the friction holds and then the friction gives way and the piece falls 2 or 3 feet and stops again, the tree bends and everything recycles... that's shock loading, plain and simple. Easy to avoid that with a professional groundie and a block.


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And don't get me wrong, in rigging scenarios, the skill of the roper cannot be understated or taken for granted. A smooth run can reduce the dynamic loading considerably.

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A better word would be dramatically. In the right situation a groundie can get big wood down safely with less than 1X on the anchor.


When you 'reduce' the force on an anchor with rope angle you are actually redirecting a portion of the force so it's acting in a different direction. That's a double edged sword too because anchors tend be strong in some directions and weak in others.


Last thing. For the friction to actually reduce the 2X anchor load, the friction surface must be AT the anchor. If the rope runs over 20' of trunk down low but then passes through free air to the crotch, the crotch still sees the 2X.
 
Nice find,
He made a mathematical error (or typo) on the last example.. should be 220 lbs from LD to natural crotch, not 200. Which throws off the rest of the math. Also he failed to give example of floating false crotch with a block, which is much more relevant than a LD. The load on the tree would be far more in that situation.. I said something to thart effect on Jamin's video....

Of course those illustrations don't get into shock loads, which are more of a concern in many situations..
 
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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.

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With an arborist block, the lowering rope helps absorb the shock through the entire length of rope "in the system". With natural crotching, mostly the "working end" helps with absorbing the shock, due to the friction at the natural crotch.
 
I just did this in my shop. Granted alot of variables arent present bbut heres what I did.

I riged a white oak limb from 2 straps to a dynamometer..Zeroed it out. Then ran a rope over the limb(natural crotch simulation). Hooked a 5 gal pail weighing 25# to 1 end and hand held the other.

Then I hooked the same pail up and Fed the rope through a block tied to the limb with a cow hitch.


On both systems I ran multiple tests.

I first pulled the pail off the floor steadily to the limb then lowered the pail to the floor.

The results:

Natural Crotch: pulling down to raise pail created a max force of 105#
Lowering it on natural crotch saw a max force of 50#

Through a Block:pulling down saw a max force of 40#. Letting the pail down created a max force of 30#.

I did 10 of each test and saw no variation. I know there was no shock loading but these are my results. What do you think. What should I change to retest.



The first pic is the NC set up
 

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