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Old 17th March 2008, 06:52 AM   #15 (permalink)
Ekka
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Join Date: Jan 2007
Location: Brisbane
Posts: 7,678
Default Re: Convert me from Natural crotch to Arbor block

Dynamic loading.

Great question NG

I would say that there's more dynamic loading on the rope in natural crotch rigging than using a block.

When running through a block the load is absorbed by the rope over a greater length.

When the rope is through a natural crotch especially if wrapped as shown then there's a lot less rope to absorb the shock.

Now that's shock load on the rope not necessarily the anchor point, there's a difference.

In the Art & Science of Practical Rigging they put a dyno on the block to measure forces. Now on a well run piece the block still recorded a load of 7x weight of cut piece. In a locked off situation it went 11x

Now I assure you that if they could somehow measure the forces on the crotch of natural crotch rigging it wouldn't be so high and in a locked off situation not as high.

It would be possible to duplicate this theory and turn it into fact if I had a darn dyno.

On one example we tie the load to the dyno and dump it, that's a locked off natural crotch.

On the other we run the rope through a block to the ground and tie it off down there, the dyno is attached to the block and the tree then dump the same load same fall distance. I bet I know which will be worse, of course the one with the pulley coz of the doubling effect however as far as the rope is concerned there's a lot more of it to absorb the shock and could actually be less.

Is this making sense or do I have to go to paint shop?

Two things to consider, load on rope and load on anchor/crotch.
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