swinging some white oak limbs

What kind of damage?

I've seen a man reach his bare hand right inside a human body and pull out cysts and blood clots.. Do you beleive me? or would you like to see the science?

Maybe it does occur. I never said it doesn't. I just ask for some scientific support. I would think with as long as I've been doing treework ,I would have noticed related damage to trees, some years down the road, but I never have. Maybe I just never put it together..
 
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I always natural crotch rig, when I AM concerned with reducing force on a tree that has structural issues..

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Daniel, can you explain that please

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Yes I can.. I think its pretty obvious too...
when you're rigging in a tree with questionable structure, and your life depends on the tree holding, you use every little thing you can to throw the odds in your favor. Natural crotch friction reduces the MA that a 2:1 pulley system has, thus putting less force on the tree.

That's why I don't use double braid.. it can't take the beating. I always want to have the option of going natural crotch.
 
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Natural crotch friction reduces the MA that a 2:1 pulley system has, thus putting less force on the tree.

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I'm not sure I agree here. That a block adds a mechanical force to a rigging system I agree with, but that removing the block in place of natural rigging removes that force I am not sure I agree with.

If we're talking hazard trees, then we can place more blocks in the system to spread the force around different points in the tree...does this increase the mechanical force acting on the tree relative to the anchor points? Yes, but I would argue that the system in general is safer and more efficient than if one were to redirect a natural crotch system through more unions.

Natural crotching is what I use when a tree has little to no potential for failure due to the presence of defects and I can work it out fast. I mostly natural crotch as well, but will always set a block on trees that are being retained. I always use a cambium saver as well...even on removals, friction is not a climbers friend and where I work now and have worked before, poplars are common climbing trees. I've seen the results of enough trees which have been natural crotched to know that the saver is the way to go. Besides, why work harder than you have to? It takes little time to set a saver.

In your example with a 2:1 system, imagine setting up this system without blocks, using only natural unions. Are you suggesting that there is less force on this system than if one were to use blocks? What about the force of friction? I would imagine that there would be more force acting on the component parts...this is why the block and tackle exist.

I'm not trying to bash you Daniel, at least your vids and posts elicit discussions and challenge us to re-examine our preconceived notions.

Made me think a little this morning anyways.
 
A block in a tree is not 2:1, it's just a redirect, there is no MA, there is extra load.

The only additional loading happens if the block is secured with a seperate rope over a crotch, running down to the ground and tied off. Then the loading on the block is doubled for every weight added into the system.

Correct?
 
A 100lb load hanging motionless on a line running through a frictionless block (down to a groundman or porty) will put 200lb force on the rigging point. The same motionless 100lb load hanging on a line running through a high-friction natural crotch will put less than 200lb on the rigging point. If the friction is so high that the rope will not run, the force on the crotch will drop to near the 100lb mark.

As soon as things start to accelerate/decelerate, everything changes, and there's a good chance that with an experienced rope person you will put less force on the rigging point while using a rigging block than you would if using the natural crotch to lower. This will vary according to circumstance (rigging from above or below the rigging point, size of loads, friction of natural crotches), but typically the greater modulation offered by a friction device (port-a-wrap, GRCS) will enable the rope person to decelerate the load more slowly, putting less of a peak force on the rigging point.


Shoot I haven't typed that much here for eons seems like...
 
I read it as mechanical force, not an advantage. Consider; to lift a 20 pound load via a rope through an overhead block, one would have to apply greater than 20 pounds on the running end of the rope. The mechanical force generated by this action would show slightly greater than 40 pounds on the block.

Perhaps this is the 2:1 to which Daniel refers.

I was attempting to point out that removing the block from the system and natural crotching (or unioning to be PC
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) does not mean that the mechanical force disappears. I believe it is still there, perhaps in addition to force present due to increased friction.
 
I hope these thoughts come out sorta clearly, its 10:20 and time for dinner, and I'm kinda tired.


If you are not redirecting (causing 2:1 loading on rigging point), but using the tree at the rigging point for your friction (or using a LD aloft), and effectively decelerating the load, I think that you will reduce your forces.

If you increase your drag by natural crotching through multiple crotches, and effectively decelerating wood, I think you will reduce your forces.

A LD and block redirecting the rope make it easier to judge your friction, and effectively decelerate your load than the variability of NC rigging.

Its harder to effectively decelerate your load with NC rigging versus block and LD rigging, so sometimes your impact force will be higher if you don't decelerate it well.


Another aspect that plays into both NC and False crotch (block) rigging is how the forces load the stem (laterally versus compression of the stem).



Today, we had to catch two of three tops in an alder where the original leader had broken, so we had decay in the top. I set a half-hitch around a large branch crotch (the half hitch only holds the rope in place so it doesn't jump off- hope that's clear) and used a POW. First one whizzed effectively right into the ground with the top (natural area, so the buried stake is no problem, but we needed to avoid a fence, necessitating the catch). It was bigger then the other. Nice and smooth, burned right into the sapwood. Little impact force.

Second one, maybe 1/2 to 5/8's the weigh, dropped from 2 feet above the NC riggging point, sorta locked up and shook the spar much more by comparison. Ben usually has a pretty good hand on the rope, but it was just a bit too much.

My point is that NC rigging can be harder to predict. From the ground, the roper has to estimate the crotch friction with the LD friction for the size of the piece being lowered.



If I had wrapped the trunk up high for friction, and cut and lowered the piece myself, I could have better fine tuned the friction. I tend to self-lower a lot on NC rigging in this way. Today, it was snowing, weather was turning, so I just had Ben catch the second (lighter piece) as well, but it didn't work as well.

I wasn't sure that I was in a good position to cut and lower the first bigger top myself, plus was less sure of how much to wrap the trunk for the right amount of friction.
 
Late dinner, fella! I'm not a rigging master, nor a mechanical engineer, but find the discussion of rigging forces weirdly fascinating. Perhaps because I have so much hands on to relate the theory to, and perhaps because I should have paid more attention in physics.

When we add redirects to a rigging system the different points 'share' the load. I agree that this reduces the forces acting on component parts of the tree during lowering operations whether it is blocks anchored to a tree or multiple natural crotch unions.

My question refers to Daniel's point that the use of natural crotches reduces force in comparison to blocks. Does the mechanical force generated by the use of blocks or redirecting the rope change when natural crotching? To me it seems like the same system, only with increased friction.
I've been wrong once before, but I was a child and thought that I could grow ears like Dumbo and fly. Didn't work out for me.
 
Tom,

As with the OLDS system or other lowering device in the tree, IF (and its a big IF) the natural crotch method is used effectively, with smooth deceleration, do you not think that you can reduce your peak load on your rigging point?

Here's a scenario that I would frequently find myself in:

Doug fir removal where I can cut and throw the limbs, but want/need to catch the top rather than climbing to the point of being able to manually cut and throw it. As I approach the topping point, I may leave either limbs (as energy absorbers) or stubs from branches.

If I use the stubs/ branches and the trunk for friction to the point where I need very little force on the "brake hand" side of the wraps, having friction on the tree doing all the work, would it not seem to reduce the force compared to redirecting (and setting up a 2:1 force multiplication)? This would be like having a POW/LD in the tree directly.

Again, this is with the big "IF" of the system running smoothly, and the climber can safely finish the cut and handle the rope without getting tangled in rope, etc.

I would feel more capable as the climber/ roper to be able to feather this with smaller pieces.

An important factor here also falls on the rigging rope construction. Newer Polydyne/ stretchy type rigging ropes will absorb force better with additional length of rope in the, which is a downside of lowering with friction at the top exclusively (less rope in the system). If it is a very low stretch rigging rope (where less energy is absorbed by stretch) then the friction would need to absorb more energy.

I thought SingleJack's idea of OLDS with Polydyne was a good option. (I can't say how polydyne is supposed to works in NC rigging.)

Thoughts?
 
Maybe MA wasn't the best way to describe what I meant..
the force on a tree can be reduced by using natural crotch rigging in certain scenarios. The point about allowing a piece to run properly is well taken.. though in many scenarios, there is no room to lower.
 
Pete Donzelli pointed out that there is no such thing as a 'friction saver'. There are lots of friction dispersing or moving strategies. The forces are still in the system but they're dealt with someplace else.

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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