Loopies, whoopies, ultras etc

[AHPP]

41 minutes ago, Joe Newton said:

Gotcha. Worst case force multiplication factor is 11x the load.

 

That's in the case of Rigging Point Below or "Negative rigging"

 

I have it memorised as 14x but I could have easily added a bit of my own for safety. What's your source for 11x?

 

 

Related story:

A bloke I climb for messages.

"Got a client with a big redwood. They want it down in 10m sections. No crane access. Can you rig it?"

"Can we get a helicopter?"

"Possibly but give me options."

 

I drew it up, calculated the weights and then factored in the 14x for negative, dead-stop catches. Mental numbers. Made a shopping list for four double whip systems. Four bloody thick ropes, eight safeblocs, four bollards, twelve chokers. It was thousands in gear that would be used once and frankly ridiculous anyway. Oddly enough it didn't go ahead.

 

[Joe Newton]

53 minutes ago, AHPP said:

 

I have it memorised as 14x but I could have easily added a bit of my own for safety. What's your source for 11x?

 

 

 

 

[Mark Bolam]

You’d have to be a real cretin, obviously, but what if the rigging point was WAY below the load?

 

Could it exceed 11?

[Mick Dempsey]

2 hours ago, Joe Newton said:

https://youtu.be/CH1YwShhx0I?si=eYJ-urx8Qdfxai1J

 

Watch at your own risk, old timer. Don't want you suffering an aneurysm this close to retirement. 

Very nice, lucky to have that ‘scaffold’ tree or it would have needed another approach.

Edited Saturday at 15:39 by Mick Dempsey

[Joe Newton]

16 minutes ago, Mark Bolam said:

You’d have to be a real cretin, obviously, but what if the rigging point was WAY below the load?

 

Could it exceed 11?

So I asked the same question of one of the blokes who helped write TG3.

 

The answer was no. 11 is the absolute worst case scenario with the rigging point way below the load. Any lower and the forces were less due to stretch in the rigging line dissipating the load. 

[AHPP]

Any mention of forces if you used static rope?

[Joe Newton]

1 hour ago, AHPP said:

Any mention of forces if you used static rope?

Rigging lines for arb work are generally "static".

 

Any rope will have an amount of elongation under load though. 

[peds]

As you say, they are all called "static", but are in fact "semi-static" as they do inevitably stretch a bit, unless they are a genuine zero-stretch cord made of kevlar or aramid or something. 

 

With that in mind... is there anything to be said for using a truly dynamic rope, like wot rock climbers use, for catching big falls, when you switch to negative rigging? "Dynamic" ropes can have something like 15%, 20%, anywhere up to 40% stretch... which does of course soften the blow on the anchor and is kinder to the system on the whole.

[AHPP]

35 minutes ago, Joe Newton said:

Rigging lines for arb work are generally "static".

 

Any rope will have an amount of elongation under load though. 

 

There's static and static. Double braid like Sirius is stretchier than dyneema like arborWINCH (both Teufelberger).

I'm aware this is academic. Nobody's going to snatch anything big on arborWINCH. Just curious if it was mentioned?

Edited Saturday at 17:55 by AHPP

[AHPP]

13 minutes ago, peds said:

is there anything to be said for using a truly dynamic rope, like wot rock climbers use, for catching big falls, when you switch to negative rigging? "Dynamic" ropes can have something like 15%, 20%, anywhere up to 40% stretch... which does of course soften the blow on the anchor and is kinder to the system on the whole.

 

Mainly no. High up, you let it run and catch it slowly. Low down, you have to stop it dead anyway. Usually. Perhaps some use case if you want to run the piece into the ground but have it on a line so it doesn't then bounce. Or if your rigger is crap and you have no choice but to use him. Then you have to log the heavy lobs the rope has taken. You'll be aware from rock climbing that that's only ten or twenty before it has to be retired.

 

Best solution - find a way to avoid negative rigging. The ropes are heavy and expensive and then it's violent.