shankenstein
New member
- Location
- Twin Cities
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.
Tagged Spider Leg Slings
- Thread starter shankenstein
- Start date
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
Been here much more than a while
- Location
- Suffolk, Virginia
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
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
Branched out member
- Location
- Lebanon, Pa USA
I'll post pictures of mine as soon as I get home.
Sent from my SAMSUNG-SM-G891A using Tapatalk
climbhightree
Branched out member
- Location
- Lebanon, Pa USA
Pictures of teulfenberger crane slings
Sent from my SAMSUNG-SM-G891A using Tapatalk
Sent from my SAMSUNG-SM-G891A using Tapatalk
shankenstein
New member
- Location
- Twin Cities
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...
southsoundtree
Been here much more than a while
- Location
- Olympia, WA
http://www.samsonrope.com/Documents...atically Loaded Synthetic Ropes_March2011.pdf
There is definitely strength loss with hitches and knots, depending on material used and rope bend radii.
There is definitely strength loss with hitches and knots, depending on material used and rope bend radii.
Steve Connally
Been here much more than a while
- Location
- Suffolk, Virginia
http://joa.isa-arbor.com/articles.asp?JournalID=1&VolumeID=38&IssueID=1
see the pdf here. SHows more breaking is determined by rope construction than hitch type. I would agree about strength loss however the cow is way low on the scale Timber is even lower Add in a marl or a half hitch and it reduces the force on both
see the pdf here. SHows more breaking is determined by rope construction than hitch type. I would agree about strength loss however the cow is way low on the scale Timber is even lower Add in a marl or a half hitch and it reduces the force on both
Steve Connally
Been here much more than a while
- Location
- Suffolk, Virginia
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.
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.
Steve Connally
Been here much more than a while
- Location
- Suffolk, Virginia
Yeah you'd be hard pressed to have issues with cranes that size. IMHO
flyingsquirrel25
Carpal tunnel level member
- Location
- South East, PA
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
Participating member
- Location
- torrington, ct.
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.
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
Carpal tunnel level member
- Location
- South East, PA
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.
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).
shankenstein
New member
- Location
- Twin Cities
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.
