Hauling systems: boost your 3:1 to a 5:1
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If you have a basic 3:1 mechanical advantage “Z drag” set up, and need some extra pulling power, here’s a slick way to convert it into a 5:1 system.
Advantages:
Easy to convert from an existing 3:1 system
May allow a small person to haul up a relatively large / heavy person
Requires minimal extra equipment (only 2 spare carabiners and a cordelette)
There's no change of direction at the anchor, so your pulling efficiency is increased
Easy reset
Because there are two different lines in the system, you could distribute this load across two different anchors.
Don’t have a long sling or a cordelette? You could also use the other end of the climbing rope.
Here’s how to convert a 3:1 to a 5:1.
Start with a standard 3:1 “Z” haul.
Clip a sling to the anchor. Clip a carabiner into the other end of the sling.
(If you're doing a crevasse rescue, using an untied (aka “open”) cordelette works better. Photo of that rigging is below.)
Unclip the rope from the carabiner on the friction hitch.
Clip your sling to the friction hitch.
Clip the rope to the carabiner on the end of the sling.
Start hauling!
You made a 5:1 system. Schweeeet, give yourself a high five!
For every 5 meters of rope you pull through the system, your load moves 1 meter.
In a theoretical frictionless world, you could move a 100 kg load with about 20 kg of pulling power. In the real world, your actual efficiency is probably about 3.5 to 1, but that should be enough to pull your buddy out of the crevasse.
You can increase your efficiency a bunch by having a pulley at each change of direction rather than a carabiner.
Both carabiners/pulleys are moving the same direction (toward the anchor) when you're pulling, so you don't need to reset the tractor as often.
Definitely practice with this a few times in a controlled environment. It may look simple when you're reading it here, but it can cause some brain lock when you're trying to do it under some real world pressure.
Want to see an photo and video of how to set this up with a cordelette for crevasse rescue?
How about another way to set up a 5:1: with a distinct disadvantage to the method shown here?
