Convert me from Natural crotch to Arbor block

Col2y

I use natural crotch because its simple and thats what ive been taught, but the more i look into it the more it looks like its the red headed step child of the arborist world

can anyone give me an arbor block 101 or links to one

anything and everything is appriciated because i have next to no experience with it


Cheers

Eric Frei

Both natural crotch and blocks have their uses.

Some trees/locations suit natural crotch whilst others are better with blocks.

Setting a block means climbing to the rigging point and then coming back down to cut lower limbs first. Also you can set more than one block, many combinations.

I do both, no hard and fast rules just a matter of what is best or fastest for the particular tree/site.

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juniorgilman

I would be interested in hearing some pros & cons to using natural crotch or arborist block.

It would seem that on a prune job you would want to use the block for the same reason you use a friction saver on a climbing line. I can also see not to climb to the top to set a block, if you don't have to for a smaller job or for the sake of time.

What are some of the other ups & downs?

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quercus

there's no need to get to the top to set a block... throw at the highest crotch that seems good for your needs, pull a line through with a pulley and rigging line et voila. then secure the end to the base of the tree. Et voila... natural crotching and blocking at the same time. Best of both worlds...

George Hayduke

Quercus,

Floating false crotch works for rigging and climbing but this option demands a more complex understanding about rigging to mechanical disadvantage.

Take it away=

****

Minuses for natural crotch rigging=

Increased rope wear and quick deterioration
Unknown amount of friction generated by variety of tree bark
Unknown amount of friction generated by varitey of tree diameters
Limited to only natural locations

Pluses for using blocks and pulleys

Little rope wear
Known friction in block/pulley...theoretically zero
Since the friction is managed at the lowering device the groundies can make quick adjustments to take into account the estimated log/branch weight. The groundie can dial in the number of wraps very easily.
A sling can be choked anywhere on a bare stem/branch to locate the perfect rigging point

Eric Frei

Another big minus for blocks is the doubling effect of the load at the pulley.

If you do as Quercus suggests you actually 4x the load at the pulley.

If you use natural crotch then other than the initial dynamic load the force on the lowering point is the weight of the piece. Graeme McMahon rigs out large sections and takes the wraps up in the tree to prevent the doubling effect.

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quercus

There's a time and place for everything ekka... But adjustable false crotching can be done...If the need arises and the opportunity is there, it saves some time and effort...

Eric Frei

Did I say there wasn't?

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quercus

No ya didn't...

Ace Master

Yes,most of the time i natural crotch but you can set up pulleys block anywhere in the tree when needed(less rigging thinking with blocks),also we use the blocks alot with the grcs when lifting is needed. You must always be carful of the load forces, friction, Rope heat, tree limb stress, rigging point,crossing of ropes, and the tress heath.

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jim1nz

Very good posts here. George, Ekka great.

Thought i would had, if your retaining the tree your rigging off, be sure to use a friction device as natural crotch rigging will absolutely hammer the cambium.

Also natural crotch rigging, taking wraps around the trunk with long ropes is a pain!

Some lowering systems twist ropes, especially wound laid ropes.

George Hayduke

Before you walk away from that comment you need to elaborate. This isn't true.

The load on the rigging point will double even with natural crotches. Adding a block displaces friction but it doesn't change the load.

In GM's rigging he would wrap the down rope around the tree which displaces the friction, and the load, somewhat. It's too simplistic to say that the trunk wrapping eliminates the load...not actually true.

Pete Donzelli wrote an article about how more efficient blocks displace friction and it's effect on rigging.

Eric Frei

Good point, maybe we need to expand on some techniques and variables.

In natural crotch rigging you will always have friction where the rope runs over the crotch. You'll know how much and how bad when you try to pull a load back up.

If you are wrapping up top as in this diagram always wrap from the top down or the branch outwards then toward the trunk. This will prevent the loaded line cinching the lowering rope and holding the load up.

When lowering in this fashion you will not be doubling the load at the rigging point, other than the initial dynamic shock if taking a head out etc once the load is fully braked and stopped the force on the tree is 1:1 or slightly higher depending on the wraps obviously. Here's where it gets interesting, if you are up in the tree and grab the lowering rope and lock it off up there or lower from up there then the force is a lot closer to if not exactly 1:1

However if the load was braked and held up (still, stopped etc) through a block it would be 2:1

And if it were through a suspended false crotch like Quercus says then it would be 4:1

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newguy18

I like using your method for lowering tops out.I always thought there was more dynamic loading in natural crotch rigging but it sounds like theres less according to what i understand from ekka's post anyway.

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old schooler

Eric Frei

Dynamic loading.

Great question NG

I would say that there's more dynamic loading on the rope in natural crotch rigging than using a block.

When running through a block the load is absorbed by the rope over a greater length.

When the rope is through a natural crotch especially if wrapped as shown then there's a lot less rope to absorb the shock.

Now that's shock load on the rope not necessarily the anchor point, there's a difference.

In the Art & Science of Practical Rigging they put a dyno on the block to measure forces. Now on a well run piece the block still recorded a load of 7x weight of cut piece. In a locked off situation it went 11x

Now I assure you that if they could somehow measure the forces on the crotch of natural crotch rigging it wouldn't be so high and in a locked off situation not as high.

It would be possible to duplicate this theory and turn it into fact if I had a darn dyno.

On one example we tie the load to the dyno and dump it, that's a locked off natural crotch.

On the other we run the rope through a block to the ground and tie it off down there, the dyno is attached to the block and the tree then dump the same load same fall distance. I bet I know which will be worse, of course the one with the pulley coz of the doubling effect however as far as the rope is concerned there's a lot more of it to absorb the shock and could actually be less.

Is this making sense or do I have to go to paint shop?

Two things to consider, load on rope and load on anchor/crotch.

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newguy18

So theres less load when i'm dead ending the rope,cutting,then lowering from up top then if i had a groundie hold the rope tight or tie it off.Maybe i'll just stick with natural crotch rigging.

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James Sayers

hi guys i saw you talking about false crotches and natural ,i only really use pullys because with the right ground crew and the right job eg being able to run branches there should be minimal effect on the tree but when working with unnone groundsmen i tend to use a natural crotch i might be wrong but it seems to spead the load more and you dont get so much movement ,but i might be just imagining it

Eric Frei

No, you are missing the point.

There's 2 forces.

1/ force on the rope
2/ force on the crotch or block attachment point

Natural crotch will put more force on your lowering rope and less on the crotch.

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James Sayers

yes i get the doubling of the load and all that but if you are natural crotching would not some of the load be absorbed down through the tree it just is not good for your rope and if you use crap rope you are just as likly to burn through it on your first limb you lower

Jeff Darby

Good piont, Ace, This where people let them selve's down with tools like the grcs,friction drum, They step up considerably in hardware but their technique and assessemnt stay far below their mechanical abilities, resulting in tops being riped out and down to the ground it all comes, for the lucky ones there's no targets for the others thats the end of their career.Please take time to learn how to use mechanical advantages properly.

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Eric Frei

Whether natural crotching or using a block the force is absorbed down the tree, that's a constant.

However the low friction of the block to either a lowering device or wraps below means more force at the block. With natural crotch there's more friction over the crotch so less force on the tail of the lowering rope (the end you are holding).

Remember in the last job I had the occasional piece that wouldn't come down and that was from the lowering rope running through the forks ... but if it were through a block they would have come down.

Now in a locked off rope situation like NewGuy18 was saying the block will increase the attachment point forces a lot more as there's no friction there and you'll get lots of duplication of force.

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southsoundtree

Ekka-

Seems like what Graeme McMahon was doing would work well for situations where you need extra groundie hands but don't have them.

I found myself in this situation doubly the other day. The rope was not long enough on its own to reach from the ground/ figure 8 to the block and back down. In order to lower on that line, we tied another lowering line to running end (I believe it to be properly called). We had to have the climber (me) pinch the two ropes together below the block to hold the load, while the groundie unclipper the figure 8, then lower the rest of the load with leather gloved hands.

Had we used the brake device in place of a block, they could have controlled the trunkwood being blocked down from the ground, then transfered control to the climber for the final lower on the one line. Wish I would have thought of that.

Seems that this would have reduced the doubling effect to me. Would you agree?

I know that there is a mini Portowrap marketed for use in the the tree. Do you see any downfalls to the is system. It seems that for dynamic loading, as in blocking down the stem, that there would be less rope in the system to elongate and absorb energy, so a good "soft catch" letting the rope run and slow down gradually would be extra important.

I'd be interested to hear all thoughts on this brake device up with the climber scenario.

Seems like static load would not pose any unseen threats, just dynamic.

thoughts???

Hope this isn't hijacking the thread, just seemed to be an extension of the considerations of natural crotching and block-lowering. Somewhere in between maybe.

Eric Frei

You are spot on, and people do ... do that.

Lots of smaller rigging is done with figure 8's attached to the tree aloft by the climber who cuts and rigs his own pieces.

A porty etc attached to the tree up there same.

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