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Ever look at those drawings in Crevasse Rescue books (MFOTH, remember the older editions?) and get all turned around and confused? Ya, me neither.
These Pics are from a seminar I took a few years back from Northwest Mountain School. Looking at these pictures doesn't make you mountain-ready BTW, there is plenty you aren't seeing, like padding the crevasse lip, escaping the system, building anchors, checking the victim, catching the fall, etc.
If it all ever looked confusing to you, here are a few more pics to add to your confusion, or possibly illuminate.
Another pulley on the weighted (victim end) line gives me a 3:1 mechanical advantage. I pull on the top line in the pic. My pulley weighs less than a locking carabiner and provides less friction but many just use a carabiner here.
If 3:1 is too much weight (and it can be if you only have one partner) and if you have the extra coils, you can make a 6:1 system. I was out of pulleys so I used a locking carabiner here.
The anchors aren't depicted but are two 18" pickets dead-man placed 18-20" deep each, angles at about 10 and 2 o'clock.
If this helps; cool, if not; sorry.
What is your favorite system?