GRCS and Pre-Tensioning Load Line

[chris_girard]

I believe its pretty common knowledge among tree riggers that if you’re rigging a load with an overhead anchor point (such as an arborist block/pulley) and you’re using a double braid lowering line, that it’s a good idea to remove as much slack as possible from the line by pre-tensioning it with the GRCS. This will reduce the amount of dynamic loading that occurs (once the cut is made) and in effect make it a static load.

Now, if you use that same double braid to block down the trunk wood, how much do you want to pre-tension it? Assume a worst-case scenario where the load will be snubbed off and not allowed to run.

I know that you do want to take some stretch out of the line to reduce the distance of fall and dynamic loading that will occur, but if you remove all the slack (or most of it), in effect your double braid has now become more of a near zero stretch full static line, which in a dynamic rigging operation is REALLY BAD for all components of the rigging, including the tree.

Now, if you don’t take any stretch out of the line, the load will run a little further and decelerate slower (which will reduce the load) by using some of the elongation properties in the line.

Obviously this is all theory and not practical to try and quantify, but I was just curious as to how much tension others apply to their GRCS when blocking down trunk wood and what the different implication can be.

 

[tomthetreeman]

Mark C. pretensioned one of the pieces in the rigging workshop in Providence, which turned out to be the best way to reduce the shock load short of using a second lowering point and/or line. How much is a little bit? Mark?

-Tom

 

[Norm_Hall]

I take off the winch and install the bollard when I'm drop hitchin.
Used Reg's tightening pulley to take out the stretch. Worked well.

 

[chris_girard]

Sounds like a good idea Norm. How exactly did you set it up on the GRCS frame? Did you use the pigtail to hold the tension?

Where is Reg's tightening pulley for sale here in the States, or do you have to go to the Stein website?

Thanks
Chris

 

[treebing]

the Harken in my opinion is only for lifting and definitly not for chunking blocks. bad idea. Thats not what it is made for. It sucks for "letting it run." switch it out and put on the bollard. I think its a safety issue as well. The GRCS only allows you to stand at one angle from the rig because of the way you wrap it. The bollard allows you to stand wherever you wish. Further more, the dinky pig tail should experience no load at all, so you should not stand at an angle to the pig tail when something gets dropped. If you dont have enough wraps, and you load that pigtail, it can break off and you will lose the whole load. The bollard works awesome though.

 

[Colin]

it wouldn't be hard to make one just cut one side plate off a petzle fixe.

 

[Blinky]

We generally hand tighten for blocks (no GRCS) but almost never do I have to drop wood onto a snubbed off line, so I'm banking on the groundie to minimize shock.

 

[theXman]

[ QUOTE ]
but I was just curious as to how much tension others apply to their GRCS when blocking down trunk wood and what the different implication can be.

[/ QUOTE ]

We don't use it to block down trunk wood.

We put on the hobbs for that. We use both the hobbs and grcs, sometimes on the same removal tree. (we will likely be doing this today on a really tall Tulip Tree removal)

if we didn't have the hobbs, I would definitely put in the alum bollard to "block down wood". ... hinging logs off.

what i like about the hobbs is that a good groundman can pull out several "clicks" as the log is hinging over, which shortens the length of rope from the tie to the block, then the groundman switches his thinking fast and lets it run when the log comes off. This works extremely smooth and barely wiggles the spar I'm on.

like i said, if we didn't have i hobbs I'd use the alum bollard, but unfortunately, we wouldn't be able to pull out slack much as the log was hinging over.
-----------------------------------
About the pretensioning of the rope and holding on to it:
I would imagine, if you pre-tensioned the rope, as the log hinged over, it would then at that moment get some of it's elasticity back from the shortening of the distance from block to tie point.

 

[Norm_Hall]

[ QUOTE ]
Sounds like a good idea Norm. How exactly did you set it up on the GRCS frame? Did you use the pigtail to hold the tension?

Where is Reg's tightening pulley for sale here in the States, or do you have to go to the Stein website?

Thanks
Chris

[/ QUOTE ]

It attached on the running end of the rope using a prusik cord. See Reg's video describing how to set it up/use it. Pretty slick.
I think? it's available from Sherrill. Reg was kind enough to send 1 to me to try out.

 

[chris_girard]

Just wondering Norm, have you had a chance to try Reg's pulley out on a Porty yet?

 

[Roger_Barnett]

[ QUOTE ]


I know that you do want to take some stretch out of the line to reduce the distance of fall and dynamic loading that will occur, but if you remove all the slack (or most of it), in effect your double braid has now become more of a near zero stretch full static line, which in a dynamic rigging operation is REALLY BAD for all components of the rigging, including the tree.



Obviously this is all theory and not practical to try and quantify, but I was just curious as to how much tension others apply to their GRCS when blocking down trunk wood and what the different implication can be.

[/ QUOTE ]

Not an issue, Chris, imo. Xman said it well :
----------------------------------
About the pretensioning of the rope and holding on to it:
I would imagine, if you pre-tensioned the rope, as the log hinged over, it would then at that moment get some of it's elasticity back from the shortening of the distance from block to tie point.

what i like about the hobbs is that a good groundman can pull out several "clicks" as the log is hinging over, which shortens the length of rope from the tie to the block, then the groundman switches his thinking fast and lets it run when the log comes off. This works extremely smooth and barely wiggles the spar I'm on.

--------------------
X

I've pretensioned blocks, to shorten the distance of fall, but also to aid in coaxing the load over. Can help remove the need for a tag/pull line. But, as X said, all the tension disappears as the block tips over, which then allows for rapid slack removal, to reduce the free fall before the load comes tight again, and is then let run. Great way to reduce dynamic loading, and can't be done with the fixed bollard.

With the proper amount of wraps, the pigtail shouldn't see enough force to be bent, imo. But I agree, the possibility exists.

While I negative block a lot less than many of you, I have the old Hobbs with no exit fairlead (I should have one put on) so can only stand in line with the wraps, and thus prefer the GRCS w/ pigtail. But the Hobbs is better for big wood, as the capstan can handle more wraps and larger line.

 

[southsoundtree]

[ QUOTE ]
[ QUOTE ]

-----------------------------------
About the pretensioning of the rope and holding on to it:
I would imagine, if you pre-tensioned the rope, as the log hinged over, it would then at that moment get some of it's elasticity back from the shortening of the distance from block to tie point.

[/ QUOTE ]

I'm going to take a little info from the rock climbing world where dynamic/ stretchy ropes are used. Someone please correct me if this doesn't apply to tree ropes.

After a Significant leader fall (where the climber is in the negative blocking scenario and might fall 20, 30, 40 feet) the climber is supposed to clip into the cliff directly to take all load off of the rope to let it "rest" for a few, 5, 10 minutes so that the elasticity of the rope can "re-set".
This does and doesn't happen.



I don't know if any elasticity is regained in the split second from the log hinging over, to freefalling, to stretching the rope again.

 

[Norm_Hall]

[ QUOTE ]
Just wondering Norm, have you had a chance to try Reg's pulley out on a Porty yet?

[/ QUOTE ]

Yeah, it's a little challenging trying to keep the tension on it as you pull down on the 3 to 1. Tried it just the wrap inside the retension bar and also with a full wrap on the long leg. Lots of friction with a full wrap. Hard to keep the tension with just the wrap inside the retension bar.