Tagged Spider Leg Slings

I've been trying to do some research and figure out the MBS and safety factor of WLL of the Chisolm crane slings. Treestuff lists the WLL as 8,400lbs for a choker. Is that a 5:1 safety margin? By "choker", does that mean just tying of the working end with a cow hitch or some similar hitch to the pick? Anybody have pictures of the tags on these slings?
Good question! Choking knots can reduce the MBS up to 50% so I assume that's what they're factoring. I was under the impression that the WLL was 10% of the MBS though.
 

Steve Connally

Well-Known Member
The timber hitch and cow hitch are not Knots. They are hitches. Its a locked version of the tensionless anchor with a virtually zero strength loss. Generally for rigging the factor is around 5%. I have them in the truck. I'll take a look when I get a chance
 

cbchris17

New Member
The safety margin seems to depend on application and other factors. The company I work for likes to use 10:1 safety margin for rigging applications. It would make more sense if these slings used a 5:1 safety margin, I can't see these slings having MBS of 84,000lbs. I want to start using these slings but figured I'd try to get more info before asking the bosses to buy them. Right now we just use whatever the crane operator has on the crane, usually round slings with shackles.
 

climbhightree

Well-Known Member
The safety margin seems to depend on application and other factors. The company I work for likes to use 10:1 safety margin for rigging applications. It would make more sense if these slings used a 5:1 safety margin, I can't see these slings having MBS of 84,000lbs. I want to start using these slings but figured I'd try to get more info before asking the bosses to buy them. Right now we just use whatever the crane operator has on the crane, usually round slings with shackles.
I'll post pictures of mine as soon as I get home.

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The timber hitch and cow hitch are not Knots. They are hitches. Its a locked version of the tensionless anchor with a virtually zero strength loss. Generally for rigging the factor is around 5%. I have them in the truck. I'll take a look when I get a chance
You're right, though some sources describe hitches as a sub category of knots.

I do believe that there is a significant strength reduction from the cow hitch since there is a rope bridge that's choking. I believe there is less strength loss with a clove hitch. Maybe someone here will school me on this though...
 

Steve Connally

Well-Known Member
Additionally. In the dead eye crane sling set up, I personally would never use one sling alone much less at the rated strength. I use minimum 2 and usually 3. It's not a dynamic load either. I have done 11k pics with three of those slings in use on the same pic. Taking into account, angles off the hook and balancing, they are pretty close to sharing the load between 3 slings. On big wood with branches I choke the trunk with a heavy sling and use slings for balance. They will take some of the load but if rigged in the proper configuration they will not take the entire load. The key is to know how and when to use a proper tool for the job. I personally have not taken a pic too big for 3 dead eye slings. It's usually outside of the lift capacity of the crane.
 

cbchris17

New Member
Thanks for the info everybody. I got the approval to use these slings at work, now I need to convince some of the older guys of the benefits of using these slings. One guy in particular was worried about the WLL and if he would have to take smaller picks ("If I gotta go smaller than what the operator tells me he can pick, I ain't using those things..."). He's an excellent climber and has tons of crane experience but is stubborn. Steve, I'll definitely be paraphrasing your last post when I talk to this coworker, i.e. load sharing, using round slings and the endura braid slings as balancers. Like you said, we mostly rent 35-40 ton cranes so usually we can't take picks that would exceed the WLL of these slings anyway.
 

flyingsquirrel25

Well-Known Member
. Like you said, we mostly rent 35-40 ton cranes so usually we can't take picks that would exceed the WLL of these slings anyway.
Unless you are close to the tree, being able to pick more than the those slings are capable of can be difficult with that size crane. I find it's more my landing zone that limits the pick anyhow. If I have a crane out (most times) I don't have huge expanses of open territory to work in. It's also important to use the sling that makes the pick go the best. Spiders are great for tops and off balance wood. But the round slings are much quicker for straight wood or wood with balanced limbs. Normally we have all our sling off to the side of the chipper or end of our LZ and it's an easy change if the climber wants/needs something different.
 

dbl612

Active Member
Unless you are close to the tree, being able to pick more than the those slings are capable of can be difficult with that size crane. I find it's more my landing zone that limits the pick anyhow. If I have a crane out (most times) I don't have huge expanses of open territory to work in. It's also important to use the sling that makes the pick go the best. Spiders are great for tops and off balance wood. But the round slings are much quicker for straight wood or wood with balanced limbs. Normally we have all our sling off to the side of the chipper or end of our LZ and it's an easy change if the climber wants/needs something different.
in essence, the use of spider legs is an important component of your lifting gear. they should not be treated as the main lifting method if simpler rigging can be employed.
 

cbchris17

New Member
Normally we have all our sling off to the side of the chipper or end of our LZ and it's an easy change if the climber wants/needs something different.
I'm all about ideas like this that makes things smoother and more productive. Up to this point I've only used round slings and shackles but have had many times it would have been easier to throw a spider leg or two on the pick to help balance it. The spider legs will just be another tool in the toolbox.
 

flyingsquirrel25

Well-Known Member
in essence, the use of spider legs is an important component of your lifting gear. they should not be treated as the main lifting method if simpler rigging can be employed.
Correct! They are just another tool that gets employed as we see necessary. Many times the actually get used in conjunction with a heavier round sling and shackle. It all depends on size, balance and obstacles.

I'm all about ideas like this that makes things smoother and more productive. Up to this point I've only used round slings and shackles but have had many times it would have been easier to throw a spider leg or two on the pick to help balance it. The spider legs will just be another tool in the toolbox.
It works very well for us. But I can see an inexperienced ground crew or a crew with no comm sets having an issue with it. The climber needs to be looking at the next piece as soon as the current one flies away, because the communication needs to happen before the ground guy taps out for noise reasons (which is normally right after unhooking).
 
Unless you are close to the tree, being able to pick more than the those slings are capable of can be difficult with that size crane. I find it's more my landing zone that limits the pick anyhow. If I have a crane out (most times) I don't have huge expanses of open territory to work in. It's also important to use the sling that makes the pick go the best. Spiders are great for tops and off balance wood. But the round slings are much quicker for straight wood or wood with balanced limbs. Normally we have all our sling off to the side of the chipper or end of our LZ and it's an easy change if the climber wants/needs something different.
I agree with everything you've said. We work in the Twin Cities metro so the LZ is always cramped! It's also amazes me how much smaller branches look when they're still attached to the tree. Everything seems longer when it hits the ground.
 
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