MA in the real world

In a previous post, I did a little testing of 1:1 pulls redirected through various devices. Now, I wanted to see how things worked with some actual mechanical advantage.

I tested various rigs of 3:1, 2:1 and 2:1 “far end haul” systems.

Here’s what I used, and here’s what I found.

Components:

• Anchor about head height

• 10 pound barbell weight

• Two reasonable quality rescue pulleys 

• 9 mm dynamic climbing rope

• Sterling hollow block or WIld Country Ropeman as a prusik

• Digital spring scale

• Various carabiners (Petzl Attache rounded stock, Black Diamond Neutrino and DMM Revolver)

I tied the end of the rope directly through the barbell weight for the 3:1, ran it up through the anchor, and set up pulls using different gear. For the 2:1 tests, I ran a short runner through the barbell plate and clipped the rope to that.

I did several slow, steady, pulls on the rope and recorded the most common number from the scale. 

This is hardly a scientific test by any means, but I think I can give a pretty good idea of relative efficiencies. Try to replicate this yourself. All the extra gear you need is a 10 lb weight and a spring scale, about $11 on Amazon.

My testing set up looked like this:

What do we see here?

• 2 pulleys in a 3:1 gives the most efficiency, but it’s still basically a 2:1 in the real world.

• If you have just 1 pulley, put it on the load strand of a 3:1 to get the most efficiency.

• Not much difference between round stock and non-round stock carabiners, use what you have.

• A 2:1 with a pulley required the same pulling force as a 3:1 with carabiners. You may want to use the 2:1, because you get more lift with your pulling strokes.

• Use a pulley with a far end haul - using carabiners gives a less than 1:1 mechanical advantage.