NebClimber
ArboristSite Operative
I've decided it is time I start knowing the working capacity of my equipment rather than guessing. But I don't know how to account for the loss of strength due to knots and hitches I use.
Please help.
I'll set up an example, first listing the rated capacity of my rigging gear:
Sampson bull rope: 8,500# tensile
block: 2 ton
whoopie: 3,380 WLL
loopie: 3,000 WLL
Example: I girth hitch the whoopie to the base of the tree and install a port-a-wrap. I girth hitch the loopie high in the tree and install the block. I run the bull rope through the block, and tie it to piece to be removed with a running bowline. Assuming a static load, what is the biggest piece of wood this system can lower (assuming I want to work at 10% of tensile strength)?
At first blush, the answer appears to be 850# (i.e., the WLL of the weakest link in the system - the bull rope).
But I have not accounted to strength lost in knots, hitches, etc. So how do I figure this out?
Steven
Please help.
I'll set up an example, first listing the rated capacity of my rigging gear:
Sampson bull rope: 8,500# tensile
block: 2 ton
whoopie: 3,380 WLL
loopie: 3,000 WLL
Example: I girth hitch the whoopie to the base of the tree and install a port-a-wrap. I girth hitch the loopie high in the tree and install the block. I run the bull rope through the block, and tie it to piece to be removed with a running bowline. Assuming a static load, what is the biggest piece of wood this system can lower (assuming I want to work at 10% of tensile strength)?
At first blush, the answer appears to be 850# (i.e., the WLL of the weakest link in the system - the bull rope).
But I have not accounted to strength lost in knots, hitches, etc. So how do I figure this out?
Steven