Strongest Block Attachment Sling

[Reg]

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Could someone please clarify what is meant by "negative" when it comes to rigging down chunks? Do you mean using a false crotch and block and pushing the piece off into a lowering line? I know the thread is about slings...thanks for the input.

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where the block is set below the falling limb/log

 

[southsoundtree]

Reg,

Thanks for adding in that point about equalizing the resistance force on each line via a prussiked line #3. This is not something that I had thought about when envisioning a scenario to employ this double block method. It surely would be hard to halve the forces on the lines.




What are you using to sling those blocks? Are you using a green log chart for those, or just experience, and crane scales? What would you guess on the weights of that chunk your catching in the picture?


In one of your videos, there seemed to be a clear shot to bomb wood, but you rigged it down. Was there a target below (utility line or something) or are people just more willing to pay for lawn damage mitigation through rigging, or...?

 

[allmark]

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Thinking about it further it seems to me it covers many similar things the fiber would experience in our application. Abrasion, twisting, compression, shock loading. Though I'd like to see something on the heat and friction part of it cause surely there had to be some friction and heat created somewhere if they "shock loaded" it.

[/ QUOTE ] Shock load may not weaken it in that study but surely it would cause it to break at a high enough point. What percentage of capacity were they using to shock load? That would be the question.

 

[moray]

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moray:... what heat was produced was distributed throughout the rope mass and wasn't enough (probably not nearly enough) to cause a large temperature rise...

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I decided this needed further checking. Fortunately the Yale Cordage web site provides beautiful charts showing the performance of some of their ropes. These specifically show, in foot-lbs, the maximum amount of energy that a pound of rope can absorb before it breaks. Even though this varies a bit by rope construction, they show a Dyneema (Spectra) rope can absorb 5,000 ft-lbs while a polyester double-braid can absorb 11,000. Converting these numbers to metric units to make the math easier, we have the HMWPE (Spectra) absorbing 14.9 kilojoules per kg, and the polyester absorbing 32.9. Now if you pour 14.9 kilojoules of energy into a kg of anything, it will warm it up. How much depends on the nature of the material. Water has one of the highest heat capacities known, and it takes a lot of energy (kilojoules) to raise its temperature. It is easier to warm up HMWPE, and easier still to warm polyester.

The result: the 14.9 Kj raises the temperature of HMWPE by 12.2 degrees F, and the 32.9 Kj warms the polyester by 45.5 degrees F. This is an absolute worst case. Clearly the mere loading and stretching of a rigging rope or sling cannot inject enough energy to raise the rope temperature very much. When ropes melt it is from excessive surface friction.

 

[Reg]

[ QUOTE ]
Reg,

Thanks for adding in that point about equalizing the resistance force on each line via a prussiked line #3. This is not something that I had thought about when envisioning a scenario to employ this double block method. It surely would be hard to halve the forces on the lines.




What are you using to sling those blocks? Are you using a green log chart for those, or just experience, and crane scales? What would you guess on the weights of that chunk your catching in the picture?


In one of your videos, there seemed to be a clear shot to bomb wood, but you rigged it down. Was there a target below (utility line or something) or are people just more willing to pay for lawn damage mitigation through rigging, or...?

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I now have a couple of 1in double-esterlon, although only used in the second video....the others were 3/4

http://www.yalecordage.com/arborist-rope/rigger-s-line/double-esterlon.html

The log in the photo was probably about 500kg.

No I don’t use a log chart.

I could have safely bombed the logs in the first vid but the customer was very particular about his lawn.

I have melted and scorched so many new slings in the past using a single line, and they are not cheap to keep replacing....so for me at least, load sharing is a good alternative.

 

[Norm_Hall]

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i'm having a couple made by 7/8" double braid eye slings made just for that purpose now norm. my guy at pinnacle arborist supply says a one inch spliced double braid won't fit into a 3/4" arborist block. i have never tried it personally, are you sure a one inch sling will fit norm? because i would rather have a couple of 1" slings than a couple of 7/8" slings.

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Yes, a 1" spliced eye sling, double braid, will fit in the CMI RP131.

 

[jduvall]

What size sling is in the blue pulley and is it the largest it will accept?