Rapid Fire Rigging Questions

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Treehouser
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Jan 30, 2023
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Michigan
  1. I do a lot of spider leg balancing using klemheist prussiks, but was never taught the how and why. I want to dial in the details. I could describe how I do it – and that I haven’t messed one up in 2022 or 2023, but I’m always a little anxious, and sometimes they don’t stay exactly how I wanted them to – so obviously I’m eyeballing it more than I should. I’ve looked but can’t find videos or threads on this. Can someone either break down the details or point me to a reference?
  2. I was taught estimating the dynamic load of a piece of wood using the ‘weight + weight x(drop distance +1 in feet). So a 200 lb log with a 4 ft drop (from center of mass) is 200 x (4+1) = ~1,000 pounds. Do you guys use this method, or something different? (and yes, I have the samson log impact ‘rigging wheel,’ for when it counts... but how often do you pull that out?). I’m good with mental math and would love to learn a different ‘rule of thumb’ and why you think it’s more accurate.
  3. How much do you guys adhere to the 6:1 bend ratio, and how important is it for rope longevity? Or are you much like my mentor who runs 3/4" rope on 2.75" sheaves and doesn't worry about it?
    1. Do we all agree that a ‘rig and ring’ friction saver like pictured below (where max ‘sheave’ on the #3 thimble is 2”), that the rope would have a 90-degree bend and use half of the #3 thimble (so 1”), then another 90 degree bend around the #2 thimble (~0.75”). A total of ~1.75” rather than the often advertised ~ 4?” And for that reason this rig n ring, or similar products, are not for ¾” rope (unless exclusively used as redirect)?
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bend radius isnt as big of a deal IMO, ive negative rigged on rope snaps in a pinch
and yes, it is 2 tight bends instead of one large one like people say
I would run 3/4" line in a rig and ring all day every day if given the option
i dont use any rule of thumb for log weight generally, I just eyeball it, never had an issue although as with 99% of the things I do I dont condone it
6:1?, a 3/4" line would need a 4.5" sheave or ring, quite large and heavy if you ask me, mine is like 3" and works just fine, every knot you tie has a 1:1 bend radius
 
1. Not sure what you're asking exactly but here goes. I assume you're using spiderlegs to try to balance a limb over structure and they keep moving on you in unpredictable ways. All pieces have a center of gravity (cog) and with a spiderleg setup you are setting multiple slings on either side of it giving a much better control over a single sling pic, but the problem remains that the system will adjust itself so that the cog is directly under the hook. You can try to get it right by tensioning the tip side so it bends up hard when tensioned which means you have control over the tip (usually the part you don't want to swing down), but it leaves a lot to be desired.

For me at least spiderlegs are a slight step up from a single line in control, but they aren't good enough for rigging leads over houses. For that i greatly prefer 2 lines since it gives so much more control. It sounded like you recently bought a grcs, and so you'll want to use that on the tips then another rigging device for the butt. While you can crank leads up just like you could with a crane, it's far easier and quicker to simply swing them, so rather than notching it to fold up, notch it towards the open area. Come up on the tips to take the weight from the limb, then after doing the cuts and climbing to a safe spot you can have the ground guys initiate movement with a tag line (tied on the tip obviously) pulling it to the open area. When the hinge finally breaks the butt will drop a bit as the butt line takes the load, and the limb can be manipulated in the air to adjust how and where you land it. Here's a terrible picture of this setup set from the ground to pick this limb off of the roof.

20210108_083406.jpg


2. The actual formula for force of a falling object is F = ma, m being mass and a being acceleration, which is 9.8 meters (~32 feet) per second per second on earth. So for every second it falls it's going faster and faster, constantly accelerating until air resistance accelerates it fast enough to where the forces equal out reaching terminal velocity. To fully explain these relationships requires calculus, but my point is your linear formula isn't this. The longer an object falls the forces go up exponentially, so i wouldn't use that at all. Just know that the longer it falls the worse it is, and it's gonna be a multiple of the weight so error on the small side when negative rigging, and don't do it unless you have to.

3. Bend radius is very important in rigging, it determines how fast your ropes wear out or can even snap them. When a rope is bent while under load, the fibers closest to the sheave go from being under tension to under compression as the load is taken up by the outer fibers. The heavier the load and the sharper the radius compared the more you'll stress the outer fibers, which is what wears ropes out and causes cut lines. 3/4 line implies very very heavy pieces, so using small blocks/ rigging rings with large rope is simply inappropriate since your efficiency is going to drop so much that you might as well use smaller ropes correctly.
 
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  • #4
1. Not sure what you're asking exactly but here goes. I assume you're using spiderlegs to try to balance a limb over structure and they keep moving on you in unpredictable ways. All pieces have a center of gravity (cog) and with a spiderleg setup you are setting multiple slings on either side of it giving a much better control over a single sling pic, but the problem remains that the system will adjust itself so that the cog is directly under the hook. You can try to get it right by tensioning the tip side so it bends up hard when tensioned which means you have control over the tip (usually the part you don't want to swing down), but it leaves a lot to be desired.

For me at least spiderlegs are a slight step up from a single line in control, but they aren't good enough for rigging leads over houses. For that i greatly prefer 2 lines since it gives so much more control. It sounded like you recently bought a grcs, and so you'll want to use that on the tips then another rigging device for the butt. While you can crank leads up just like you could with a crane, it's far easier and quicker to simply swing them, so rather than notching it to fold up, notch it towards the open area. Come up on the tips to take the weight from the limb, then after doing the cuts and climbing to a safe spot you can have the ground guys initiate movement with a tag line (tied on the tip obviously) pulling it to the open area. When the hinge finally breaks the butt will drop a bit as the butt line takes the load, and the limb can be manipulated in the air to adjust how and where you land it. Here's a terrible picture of this setup set from the ground to pick this limb off of the roof.

View attachment 126665


2. The actual formula for force of a falling object is F = ma, m being mass and a being acceleration, which is 9.8 meters (~32 feet) per second per second on earth. So for every second it falls it's going faster and faster, constantly accelerating until air resistance accelerates it fast enough to where the forces equal out reaching terminal velocity. To fully explain these relationships requires calculus, but my point is your linear formula isn't this. The longer an object falls the forces go up exponentially, so i wouldn't use that at all. Just know that the longer it falls the worse it is, and it's gonna be a multiple of the weight so error on the small side when negative rigging, and don't do it unless you have to.

3. Bend radius is very important in rigging, it determines how fast your ropes wear out or can even snap them. When a rope is bent while under load, the fibers closest to the sheave go from being under tension to under compression as the load is taken up by the outer fibers. The heavier the load and the sharper the radius compared the more you'll stress the outer fibers, which is what wears ropes out and causes cut lines. 3/4 line implies very very heavy pieces, so using small blocks/ rigging rings with large rope is simply inappropriate since your efficiency is going to drop so much that you might as well use smaller ropes correctly.
i appreciate the hell out of this thoughtful response.

with respect to spider legs, before I bought the GRCS I had no way to lift a limb, so you pre-tension as much as you can, try to estimate COG, set the tip tie and spider leg equally far away in terms of weight erring on the side of the tip, notch, kerf cut, strap if needed, and slowly apply a back cut letting it tear rather than snap to diffuse dynamic force. I haven't smashed anything in ~18 months doing this, but yes, they don't always go IRL as I planned on my head. (edit:. but I guess I was hoping I could nail the fundamentals, and lift a limb perfectly horizonal using the GRCS). if that's impossible it's great to know, because I would have spent all summer friggin' around before hopefully learning that lesson)



now with the GRCS I'm figuring out what benefits ~ 2K pounds of lift can give me. I'll try your method the next time I don't have the vertical space to just stand it up straight, which has been my go-to move so far. (very limited business in the winter to play with it).



2) regarding estimating dynamic load, I appreciate the difference between linear and geometric growth. that said, there has to be a rule of thumb the pros apply in order to 1) not overload your ropes/rigging/tree, and 2) telling the groundie how many wraps to put on. I'm mostly self taught, but the few times I've worked as a groundie I've never once seen a guy with a calculator up in a tree.

my day job is essentially math and probability in a bank setting. I've literally memorized a big chunk of the 'green weight log chart' because ... that's who I am and it's more interesting than commercial banking. if there isn't a good 'best practice' rule of thumb on this' I'd be inclined to make one myself. but ai thought it was essentially 'weight + weight x(drop distance +1 in feet)' with the caveat that over say 5 ft of fall you're underestimating it.

3) bend radius: what I've read seems to suggest you are right, that bend radius is very important for ropes. my more specific question is how close to the 6:1 should I try to be. I'm a little obsessive about my ropes (comes from rock climbing) and never natural crotch, for example. my present 4K WLL blocks have a 2.75" sheave, which is 4.4 : 1 over a 5/8" rope. I was going to say that was 'good enough, probably better than many others are using.' would you advise me to spend the money to achieve 6:1?
 
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My opinion ... you are probably more than okay for now , keep rigging and you'll develop a good collection of Blocks anyways. Congrats on buying the GRCS as it is a big throw for sure ... My only down with the GRCS is it just doesn't go out enough but when needed it is THE shit and saves lots of climbing and cutting up high on the job ... really saves the whole job.
 
i appreciate the hell out of this thoughtful response.

with respect to spider legs, before I bought the GRCS I had no way to lift a limb, so you pre-tension as much as you can, try to estimate COG, set the tip tie and spider leg equally far away in terms of weight erring on the side of the tip, notch, kerf cut, strap if needed, and slowly apply a back cut letting it tear rather than snap to diffuse dynamic force. I haven't smashed anything in ~18 months doing this, but yes, they don't always go IRL as I planned on my head. (edit:. but I guess I was hoping I could nail the fundamentals, and lift a limb perfectly horizonal using the GRCS). if that's impossible it's great to know, because I would have spent all summer friggin' around before hopefully learning that lesson)



now with the GRCS I'm figuring out what benefits ~ 2K pounds of lift can give me. I'll try your method the next time I don't have the vertical space to just stand it up straight, which has been my go-to move so far. (very limited business in the winter to play with it).



2) regarding estimating dynamic load, I appreciate the difference between linear and geometric growth. that said, there has to be a rule of thumb the pros apply in order to 1) not overload your ropes/rigging/tree, and 2) telling the groundie how many wraps to put on. I'm mostly self taught, but the few times I've worked as a groundie I've never once seen a guy with a calculator up in a tree.

my day job is essentially math and probability in a bank setting. I've literally memorized a big chunk of the 'green weight log chart' because ... that's who I am and it's more interesting than commercial banking. if there isn't a good 'best practice' rule of thumb on this' I'd be inclined to make one myself. but ai thought it was essentially 'weight + weight x(drop distance +1 in feet)' with the caveat that over say 5 ft of fall you're underestimating it.

3) bend radius: what I've read seems to suggest you are right, that bend radius is very important for ropes. my more specific question is how close to the 6:1 should I try to be. I'm a little obsessive about my ropes (comes from rock climbing) and never natural crotch, for example. my present 4K WLL blocks have a 2.75" sheave, which is 4.4 : 1 over a 5/8" rope. I was going to say that was 'good enough, probably better than many others are using.' would you advise me to spend the money to achieve 6:1?
Ropes are consumable items. I very, very frequently natural-crotch on removals, and lots of pruning jobs if I can burn the tree on a spot that will be pruned off (sometimes using a sling and biner a bit toward the tip from the NC point to keep a natural crotch wrap from creeping to the crotch/ branch collar, which needs preservation) with 1/2" rope.

Double-braids are not so durable for NC, rigging, so I use hardware for my 3/8", 1/2", 9/16" and 5/8" double-braids, almost never using my GRCS.


Laying down or speed lining more numerous, smaller pieces with less set-up/ break-down can be easier and faster on both the climber/ bucket-op, and the ground crew. Double-whip tackling doubles the WLL of your ropes. Other times, it's better to set up bigger stuff on bigger gear.

A lot is market and species dependent.

Keep your options open.

$.02
 
Ropes are consumable items. I very, very frequently natural-crotch on removals, and lots of pruning jobs if I can burn the tree on a spot that will be pruned off (sometimes using a sling and biner a bit toward the tip from the NC point to keep a natural crotch wrap from creeping to the crotch/ branch collar, which needs preservation) with 1/2" rope.

Double-braids are not so durable for NC, rigging, so I use hardware for my 3/8", 1/2", 9/16" and 5/8" double-braids, almost never using my GRCS.


Laying down or speed lining more numerous, smaller pieces with less set-up/ break-down can be easier and faster on both the climber/ bucket-op, and the ground crew. Double-whip tackling doubles the WLL of your ropes. Other times, it's better to set up bigger stuff on bigger gear.

A lot is market and species dependent.

Keep your options open.

$.02
... yep , many times for me the Speedline is the most efficient way to solve problems ... also if the Big Dog is eating , I have found that extra Blocks and Line Length make for versatility with the Harken ... using other Trees , stuff like that
 
every knot you tie has a 1:1 bend radius
And that's why you loose a good 50% of the rope's strength most of the time with the knots.
When I looked for the bend radius thing, I found a detailed answer on a site dedicated to the wire ropes for cranes.
Actually, the rope has its nominal strength when it lays purely in line. As soon as it takes a bend, even a slight one, it looses some % of the strength. The more the rope is bend, the more its strength's loss increases. The deal with the 6/1, or whatever you choose, is that it gives a % of loss within an "acceptable" limit. If you don't aggree with the standard practice in industry, you can define the loss good enough for you, then you have "your" bend radius's reference for a given rope. Fine ?

If you think of it, who cares if the sheave reduces the rope's strength by 15 % when the knot to hold the load reduces it by 50 % ?

edit: A tight bend radius weakens the rope by an uneven loading of the fibers, but too makes the fibers slip more again each other and therefor wear more internally.
 
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Do we all agree that a ‘rig and ring’ friction saver like pictured below (where max ‘sheave’ on the #3 thimble is 2”), that the rope would have a 90-degree bend and use half of the #3 thimble (so 1”), then another 90 degree bend around the #2 thimble (~0.75”). A total of ~1.75” rather than the often advertised ~ 4?”
Almost. To me, that's two separated bends of 90° (more or less, along the real position of the two rings related to each other), yes. But though, as one is 1" and the other is 0.75"( I take your numbers), it isn't 1.75" as a total radius but still only 0.75, like the tightest part.
 
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  • #11
And that's why you loose a good 50% of the rope's strength most of the time with the knots.
When I looked for the bend radius thing, I found a detailed answer on a site dedicated to the wire ropes for cranes.
Actually, the rope has its nominal strength when it lays purely in line. As soon as it takes a bend, even a slight one, it looses some % of the strength. The more the rope is bend, the more its strength's loss increases. The deal with the 6/1, or whatever you choose, is that it gives a % of loss within an "acceptable" limit. If you don't aggree with the standard practice in industry, you can define the loss good enough for you, then you have "your" bend radius's reference for a given rope. Fine ?

If you think of it, who cares if the sheave reduces the rope's strength by 15 % when the knot to hold the load reduces it by 50 % ?

edit: A tight bend radius weakens the rope by an uneven loading of the fibers, but too makes the fibers slip more again each other and therefor wear more internally.
agree with this, as it aligns with my research on the topic of rope strength, bend radius, and rope maintenance.

I'll also add that I periodically remove the last 15' of line 2-3 times before retiring the rope... for this very reason. that's the part that will break under heavy load, as you said b/c a knot will reduce strength ~40-60%, plus all the wear externally from the piece, and wear internally from the 1:1 bend radius, makes that area in the rope at the same time the weakest.
 
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