Alternative rigging pulleys

[High Scale]

Redirects do spread the load.

 

I agree, the highest pulley takes the majority of the load.

[John Shutler]

Re directs dont spread loads mate, load is still applied to the main anchor point regardless of and secondary anchor. Redirects as in pullys not natural crotching were brought about because of double braid rigging lines being introduced to rigging as we know it. I.E you cant natural crotch double braids like you can 12 strand, 16 strand etc etc. But they do act as a back up if you overload your main anchor.

 

sorry pal, your wrong there

"As a rule forces can be minimized by, Putting more rope in the system"

quoted from the Art and science of practical rigging

 

load is also shared between multiple anchor points

[Paul Smith]

I agree, the highest pulley takes the majority of the load.

 

Dependent on angles between the pulleys and therefore heights etc.

[aaron mj]

Ok re direct pullys do add a bend to the rope which i suppose can loosly be classed as spreading the load through friction. I agree by changing the angle a rope runs through a pully you can change forces on that pully..... but the load is the same no matter what you do. Your only really changing the way load is applied to the highest anchor point/(s) Ive only ever skimmed through the art of practical rigging i have to admit. Adding more rope?? How can this help? the force is the same........ Cheers for the help with this if im wrong its good to know but im fairly certain. vtio website has some info on force vectras

[DrewB]

imagine falling on a short bit of rope-it will hurt as no stretch. imagine falling on a 100m rope, more stretch equals less pain.

[aaron mj]

imagine falling on a short bit of rope-it will hurt as no stretch. imagine falling on a 100m rope, more stretch equals less pain.

 

Sure i understand about that, but 200kg is still 200kg the load isnt anyless?? That reduces force, surely?? which in tern reduces shock loading and there for reduces stress on the anchor points. we all know about that. Its why cord like yale double esterlon and pollydene are so popular. and favoured over static cord with far hire breaking strength. but John was talking about load spreading. opening an angle is great. but you still have a double load on the two systems rather than the one main one. In my opinion re- directs are little more than a back up and cranning point. weight is still there. and still affecting systems/anchors in the same way. i dont know many people/anyone who goes up and sets two exactly level lowering points, would be very awkward and very inefficient. if they arnt exactly level the highest will still fail under the same load as it would have with out a secondary. force is reduced but not load..............

[DrewB]

but if the force is reduced then surely the load on the anchor point is also? As i see it (and may be wrong) the 200kg is always going to ramp up massively in load due to falling weight on the anchor, so if you can reduce that load by increasing rope in th system then you can reduce the load on the anchor from ramping up so masively. of course with the wrong angles you may in fact increase the load theoretically but the rope stretch then might negate that increase. or just cut smaller bits.......

[Mark Bolam]

You're all right, sort of.

 

As Aaron correctly says, if you are lowering a 200kg lump, you will have 200kg hanging off your top anchor, you can't avoid that.

 

That is purely in weight (mass, m).

 

You can, as many have said, avoid putting any unnecessary stress onto that anchor by using additional pulleys etc. because you are reducing the FORCE (f)on the anchor, by limiting the acceleration (a) of the falling timber.

 

f = m x a

 

m is a constant, so by reducing a you reduce f, the force, i.e. stress on the anchor.

 

I've had 11 cans of Stella tonight, so I'm glad I could help.

 

Mark Bolam

BEng (Hons)

[Paul Smith]

If you have 200kg hanging of the pulley you have 400kg of force on the pulley and subsequent anchor point. 200kg on the working end and 200kg on the other end to stop it falling. By adding more pulleys you spread the force which if you are doing any negative rigging is imperative.

 

Take the 200kg example above. 1 metre free fall = 200kg X3 +1= 800kg. It doesn't take much to ramp it up!

[aaron mj]

If you have 200kg hanging of the pulley you have 400kg of force on the pulley and subsequent anchor point. 200kg on the working end and 200kg on the other end to stop it falling. By adding more pulleys you spread the force which if you are doing any negative rigging is imperative.

 

Take the 200kg example above. 1 metre free fall = 200kg X3 +1= 800kg. It doesn't take much to ramp it up!

 

Yeah thats correct and very often overlooked as well.....Perfect example of reducing (load) is when installing access line for SRT isolating an anchor with alpine butterfly as apose to running a line over each side of that limb and tieing around the base means Say 100kg climber is still 100kg not 200kg. And Drew im not talking about reducing force here i 100% agree that by reducing force you reduce shock load on that anchor point, but initial load is still there........ The reason i really think this is worth while discussing is because with new developments in cord and pullys etc massive loads can be acomplished. However i see a real future problem with anchor point loading being overlooked because of simple misconceptions regarding ''loadspreading'' which doesnt exist. Load is load is load and force minimisation is the way in which people seem to be focusing on eliminating it. Load cant be Eliminated.

 

Any way i dont usually post on important threads like this...... Mainly because i feel like some kind of old dude with nothing better to do with my time haha. But i do think its important, and more and more relevent as things get more advanced.