natural crotch or block to reduce overall force

Daniel

Daniel

Carpal tunnel level member
Location
Suburban Philadelphia (Wayne)
The below video shows a large silver maple top getting rigged off itself, old school natural crotch. There appears to be very little room to let the piece run..

You all know that the friction at the natural crotch significantly reduces the force multiplier of the rigging system, creating less force on the tree. However, the stretch in the line is reduced in the natural crotch system, which creates more of shock load and therefore more force on the tree.

So there are a lot of variables involved including the dynamic properties of the line and the amount of fricion at the NC, weight of the piece, amount of fall, length of the line, etc...

I almost always use a block for such cuts. In looking at this video, it appears that the piece was not run at all, and there is relatively little movement in the tree, compared to what I would have expected to see on a silver maple with that big of a top.

It looks like the natural crotch rigging significantly reduced the force on the tree in this scenario. Is there any science supporting that conclusion with the rigging software or elswhere?

What do you all think??? It may be more a case of the lower limbs left in tact buffering the movement of the remaining stem..

http://www.youtube.com/watch?v=bhM5zmJmEWg

I hope we can get past the lack of PPE and personalities involved, to probe for some understanding here, as this sems a bit more "relevant" than watching Tim trash a perfectly good pair of chaps, while he neglects to mention the kickback zone of the bar.
 
If i can add my opinion, take it with a grain of salt mind you on account that I lack the years of experience many of you have, but it appears to be the fact the top fell as it did that allowed for such a soft drop.

The top appears to fall off and away from the stem, as opposed to falling right over and falling straight down. As it came away, the rigging line caught it, causing a more controlled deceleration. At approximately 0:24 seconds, you see a small shudder in the top, as it goes from falling "parallel" to the ground, to forming an arc, as the rigging rope caught it, that shudder is there the rope came under tension, and therefore there was not much vertical movement to begin with, therefore there isn't much vertical speed which will result in shock loading or heavy movement of the spar. Rather, the rigging line just acted as a hinge in the system guiding the top to the final vertical position.

I hope this makes sense, i tried to explain it as best i can.

And if anyone sees a way to add to my opinion or refute it, please share, i'm looking for this to be a learning experience as well.

Thank you,

Steven
 
If you take a close look at 25 - 26 seconds you can see the movement of the tree perfectly....

A couple seconds later you can also see the rigging line crosses over itself and the tree seems to have little swing indeed for a silver maple. But some weight was left up there that helped the mass slow down.

Don't exactly know how I can explain in english but what we do over here with trees that move a lot is to leave some branches in the top and rig the top down, this slows the mass down and helps to keep the movement to a minimum.

I'm not a fan off natural crotch rigging because it makes it allmost impossible to get dynamics into the rigging system and minimize the forces.

climb safe
wouter
 
Pete Donzelli did some research that showed how using a higher efficiency pulley/block changed the load on the rigging point.

The research was published as an article in Arborist News.
 
Only a guess....

Notice how the top of the piece being taken hits the tree at the base, it absorbs much of its own energy before being sent back up the tree\rope. The top did seem to swing on the rope as SRTSteve pointed out - which if not for the top taking so much of it's own energy on impact would have given him a pretty good ride.
 
I agree with the last statement. A lot of time where we are taking a large top on somewhat of an uneasy spar, and given the space of the drop zone, we will let the top free fall, only slowing periodically to control the placement, and then a final halt once it has hit the ground to control the butt. It works rather well for shocking the spar. However I have also been in a tree where a large top has come out and hasn't been allowed to run, allowing the riggings to take the full force and I have gone for quite a bit of a ride. The ropes crossing isn't necessarily a good thing as the increased friction on the rope adds to the system changing the control of the limb, as well as burning/glazing of fibres. When rigging through natural crotches, I find the friction involved in raising a piece without the good rig involved can be a hinderance to the ground crew and take those into account when I set up my rigging.
 
The path that the top took while falling all comes back to the initial cut. Observe how shallow the initial face cut is, and remember the principal on face cuts: the larger the cut, the longer the piece will fall still being attached to the tree, until ultimately being broken off when the face closes.
At 0:08 seconds you get a good picture of the face cut. it is both shallow and not very wide, allowing for it to close up relatively quick.

The way i would understand the physics of all this is as follows:

When a top falls, there is one of newtons laws at play: "every action has an equal and opposite reaction" (follow me on this) so when a top is falling, with a very large face that doesn't break until the tree is over 45 degrees out of vertical, then there is more resulting force horizontally than vertically. Vice-versa a smaller face that breaks before the top is 45 degrees past vertical, there is more resulting force in the vertical direction... i/e down the trunk, as opposed to a horizontal force which will "throw" the spar in the "opposite direction as the force that is acting" on the top.

This particular cut then resulted in the second part of this scenario. A face that breaks quick, allows the top to fall horizontally or possibly butt down (by principal).. and away from the tree. (i have used this technique to remove a top without damaging a flower bed that was at the immediate base of the tree) while a face that is wider and takes a longer time to break, the top can fall to horizontal or even below horizontal, and depending how it breaks, it usually falls to the base of the tree as opposed to "out and away" that a small face will cause.

I hope that this made sense, i did the best i can, to sum this up, it made sense to me that the face that the climber cut, caused the top to break at a time that energy could be transferred down the spar as opposed to laterally across the top(of the spar). Secondly, once that top broke, it fell away from the tree, being caught by the rigging line (as i explained in my first post) and resulted in a gentle lowering.

I apologize for the "physics" lesson, it was just the way it made sense to me.

Thank You,

Steven
 
Nice Hard Hat. I love that American style cowboy hard hat.
grin.gif
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grin.gif
 
Good points all around, but I think the more important point is looking at the marl going around the stem and up to the cut piece. This is gonna mean that the tensioned rope drags down the bark as it is caught by the rope. Really really really super old school. I think this prevents some of the intense stem wobble we would otherwise expect to see.

Still, I don't think this is an ideal scenario to debate the merits of block vs natural crotch rigging.

At arbor camp earlier this year in Queensland, AU, Graeme McMahon had some very interesting videos of removing seriously defective trees using multiple anchors and natural crotches, each anchor utilizing a marl. He makes a good case that although this is hard on the ropes, it spreads the load out in a situation where doubling the force (as in using a block on a single anchor) could be disastrous.

For me, the take home message of that had more to do with rope vectors though: multiple anchors can be very useful when you know how to use them. Don't think I'll be trading in my double braid and block for 1.5 inch three strand any time soon...
 
[ QUOTE ]
The below video shows a large silver maple top getting rigged off itself, old school natural crotch. There appears to be very little room to let the piece run..

You all know that the friction at the natural crotch significantly reduces the force multiplier of the rigging system, creating less force on the tree. However, the stretch in the line is reduced in the natural crotch system, which creates more of shock load and therefore more force on the tree.

So there are a lot of variables involved including the dynamic properties of the line and the amount of fricion at the NC, weight of the piece, amount of fall, length of the line, etc...

I almost always use a block for such cuts. In looking at this video, it appears that the piece was not run at all, and there is relatively little movement in the tree, compared to what I would have expected to see on a silver maple with that big of a top.

It looks like the natural crotch rigging significantly reduced the force on the tree in this scenario. Is there any science supporting that conclusion with the rigging software or elswhere?

What do you all think??? It may be more a case of the lower limbs left in tact buffering the movement of the remaining stem..

http://www.youtube.com/watch?v=bhM5zmJmEWg

I hope we can get past the lack of PPE and personalities involved, to probe for some understanding here, as this sems a bit more "relevant" than watching Tim trash a perfectly good pair of chaps, while he neglects to mention the kickback zone of the bar.

[/ QUOTE ]
I havent' seen your video link, I don't have too.

I've experienced many times first hand, the effects of letting the rope run natural crotch vs a block.

Block and good groundperson wins.

I've been on 125 foot plus Tulip trees and the top is the last to go, 8 or 10 inch diameter. If the spar got shaken bad, i might have gone down with the top. With a good LD, good groundman, and good talk before hand..... the top drops and drops smooth with very little shake, if any.

Never been able to duplicate that with a natural crotch or clevis.

No mystery here. Blocks are the way to go. Natural crotch is caveman style. Step up.
 
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What do you all think??? It may be more a case of the lower limbs left in tact buffering the movement of the remaining stem

[/ QUOTE ]

With a short stocky hardwood like Rickys maple you're not going notice a great difference whatever you do Dan....exept maybe cutting a big wide notch might put you at risk if the tree was sketchy. On a hundredft bean-pole, different story. I'll stick with the block, thanks.
 
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What do you mean when you say that a big wide notch might put you at risk on a sketchy tree?

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Cause it'll yank on the top a heluva lot more where's still connected by the hingewood, whether rigging or not.

On the otherhand it can be used as a rope-saver when you are in fact rigging, but strictly on sturdy trees. I'm speaking from experience, this is not advice.
 
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With a short stocky hardwood like Rickys maple you're not going notice a great difference whatever you do Dan....exept maybe cutting a big wide notch might put you at risk if the tree was sketchy. On a hundredft bean-pole, different story. I'll stick with the block, thanks.

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The length of the rope comes into play here.. 100' of exta line to stretch is going to make a lot of difference..

on a side note.. it looks like he fouled the rigging, but he didn't.. he had it set up right...

And X I was talking about situations where there is no room to let the piece run..
 
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[ QUOTE ]
What do you all think??? It may be more a case of the lower limbs left in tact buffering the movement of the remaining stem

[/ QUOTE ]

With a short stocky hardwood like Rickys maple you're not going notice a great difference whatever you do Dan....exept maybe cutting a big wide notch might put you at risk if the tree was sketchy. On a hundredft bean-pole, different story. I'll stick with the block, thanks.

[/ QUOTE ]

Thank you for this thread. I finally learned some useful stuff from this Ricky vid.
 
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The length of the rope comes into play here.. 100' of exta line to stretch is going to make a lot of difference..

[/ QUOTE ] as is the hundred ft of leverage if your your groundperson locks up the line.

What I'm saying is that the maple in the vid is a bad example....that was never going to be critical situation however it was rigged. The only thing missing was Ricky yawning up there....he had that tree well in hand.

I've never personally felt the need to revert back to natural crotch rigging on a job since I discovered blocks....and have rigged all kinds in that time, dead, live, leaners whatever. If anyones in the position on a given day and believe natural crotching is the only way to prevent failure then they shouldn't be rigging that tree in such a way.
 
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