GRCS Forces

PUClimber

PUClimber

Location
Indiana
We were doing some rigging today and I was wondering what kind of forces are generated or can be generated by a grcs. This is not only at the rigging point but also on the two legs of the rope and even at the grcs itself. At a point you have no movement of the piece that you're dropping when you tighten up the light to take the stretch and slack out of it. If anyone has some feedback that would be great.
 
I strongly feel that you should not drop pieces on the GRCS. Use the aluminum bollard. Being able to take out the slack before bombing a piece does not make up for being a terrible tool for letting it run. Use the GRCS as a lifting device only. IMO
 
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I strongly feel that you should not drop pieces on the GRCS. Use the aluminum bollard. Being able to take out the slack before bombing a piece does not make up for being a terrible tool for letting it run. Use the GRCS as a lifting device only. IMO

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x2
As for the question. If I am reading your question right, the forces are the same as rigging with a portawrap. 150 # piece, block sees 300#, GRCS sees 150# (in a perfect, frictionless world). The only difference (over porty) is you can now lift and remove most if not all of possibility of shock loading.
 
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We were doing some rigging today and I was wondering what kind of forces are generated or can be generated by a grcs. This is not only at the rigging point but also on the two legs of the rope and even at the grcs itself. At a point you have no movement of the piece that you're dropping when you tighten up the light to take the stretch and slack out of it. If anyone has some feedback that would be great.

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Very hard question to answer as there are so many variables that go into the equation (and the equation changes with every piece taken) that I don't even think that we can answer that question completly.

For a more definitive answer, I would refer you to the HSE Rigging Report which covers a wide range of studies.
 
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We were doing some rigging today and I was wondering what kind of forces are generated or can be generated by a grcs. This is not only at the rigging point but also on the two legs of the rope and even at the grcs itself. At a point you have no movement of the piece that you're dropping when you tighten up the light to take the stretch and slack out of it. If anyone has some feedback that would be great.

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Tough question to answer definitively. Like Kevin said,the winch should be used for lifting only. But, I have had pieces break off prematurely and create some high forces that were unexpected. If I'm lowering or catchin wood, the bollard goes on.

This one should be addressed by Mr. Good, the inventor.

Tyler, sounds like you were catching wood with the winch. I don't think Mr. Goodwinch would recommend that.
 
I think that in order to really maximize the benefits of the GRCS, you need to be able to lower loads into the winch. The whole process of pretensioning to remove slack and then cutting/releasing the load can't be practically done without doing this, unless you have two units set up. I agree that dumping heavy loads into the winch is bad, but routine rigging is allowable IMO. I believe that the SWL on the winch is 2000#, so if you keep nasty shockloads under 100# and minor shockloads under say, 2-300# you should be safe. This is based on what I have seen at multiple rigging demos with the use of a dyno.

-Tom
 
Well we were winching it to get to break away from the house or to pull it towards are rigging point. I understand the forces as far as your piece is this amount of weight and all that. My question is what kind of force can be put on the rope before the piece is loose. Say the cut is not through enough and the piece is stationary or the operator says to pretension the line and the groundman cranks it till he can't crank anymore.
 
I don't think you can break a healthy rope with the GRCS, you have to be careful not to break the tree. u cant put enough force manually to hurt the GRCS, but if you don't have your fairleads lined up right, then you can bend them.


In the instructional CD, It is recomended to bomb peices using the GRCS and the ability to pretension the load is mentioned as a perk. I have had a couple of bad experiences trying to do this. I believe the winch is strong enough to handle bombing big wood but the ability to let the rope run smoothly and cleanly is lacking. the bollard on the winch is not shaped in a way conducive to running a falling load smoothly. The ropes tend to cross and bind and bing the load to a sudden unexpected stop. At slow speeds, as in raising and lowering in a controlled fashion, it is an amazing tool.

Now, I sometimes hang the portawrap on the tree if I am going back and forth between dropping loads and raising loads. The aluminum bollard works the best though.
 
On the wesspur site it says the GRCS "has a dead lift rating of 3,000 lb". So it should be able to generate 6000lb at your rigging point while winching. It's hard to say what this is based off of though. I would think the handle would fail first, but what if you're using a drill? I doubt the gearing would break. Maybe the handle is designed to fail at about this rating.
 
they dropped a volvo into the grcs with ten foot of slack and it survived unscathed with the visor plate on and got wrecked without being cut into the tree. they were using 1 1/2" line i think.
 
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Well we were winching it to get to break away from the house or to pull it towards are rigging point. I understand the forces as far as your piece is this amount of weight and all that. My question is what kind of force can be put on the rope before the piece is loose. Say the cut is not through enough and the piece is stationary or the operator says to pretension the line and the groundman cranks it till he can't crank anymore.

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Sounds like your climber needs a lesson in rigging cuts and the groundsperson needs a lesson on the GRCS and forces. I haven't heard of a rigging line parting from cranking too hard. I would be more concerned about the tree breaking. I've heard of several limbs breaking from cranking too hard.
 
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