A More Efficient 3:1 Pulley System?


Tip/Trick/Gimmick: A More Efficient 3:1 Pulley System ?


Source: Ontario Rock Climbing Association -      Safety Manual

Contributed by: Marty Comiskey ( martycomiskey@yahoo.com)


Best useful for:   Top rope      Trad   x      Mountaineering x
                            Sport      x    Ice    x        Other (list)


Description (limit to 200 words): At the recent "Leader's SKill Day" at Carderock, Md. on 4/10/10 we showed PATC members how to construct a 3:1 pulley system in the event they needed to help/aid a stuck "second" having trouble on the crux.


With any system there are pros and cons. Using the relatively simple to set up "3:1 'Z' Pulley System" here are some of its advantages and disadvantages:


Pros - simple to set up, quick to break down

Cons - lots of friction at Reverso/BD Mountain Guide ATC/belay device
     - need to 'pull up' (inefficient)
     - if rigged with re-direct to allow 'pulling down', system introduces more friction   and reduced mechanical advantage


At "Leader's Skill Day" I briefly demonstrated an alternative pulley system that some found interesting (and I promised participants I would send out this write up). I found this pulley system in the "Ontario Rock Climbing Association - Safety Manual." They called it an "Inverted Piggyback Pulley System." It is a variation of the Spanish Burton pulley system.


The Inverted Piggyback system's advantages include:
- bypass high friction at Reverso without losing its locking capability
- allows a "pull down" without the addition of more pulleys and reduced  mechanical advantage


Disadvantages include:
- it is more complicated to set up than the "Z Pulley system."
- there is more rope management involved (i.e. slack in climbing rope at Reverso)


The Inverted Piggyback system can be set up using a seperate length of cord (i.e. cordalette) or a section of the climbing rope. As one pulls down on the Inverted Piggyback pulley system, slack will develop in the climbing rope at the Reverso. This slack must be pulled through the Reverso while holding the pulley line tight to assure proper belay of "second." This is a bit cumbersome, but more than worth it for the improved efficiency of the pulley system.


I have included a diagram from the Ontario Safety Manual showing this set up. Take note that this book was written (~ 1990) before the invention of the Reverso and their diagram shows an old style locking belay rig.



    

MEMBERSHIP other Sites ABOUT
2018 PATC-MS | The Mountaineering Section of the Potomac Appalachian Trail Club | All Rights Reserved.