Where to put the pulley?
I only have one pulley. Where should I put it to get the easiest pull?
Excellent question! We often have to improvise with limited equipment, and the location of the pulley can make a difference in the efficiency of your hauling system.
You should use your “good” pulley on the position that’s closest to your pulling force (aka, your hands).
A simple explanation, in the words of rigging expert Richard Delaney: "...the best place is closest to where the effort is applied, as this preserves maximum effort moving into the system rather than wasting it at the first bend."
Or, to say it another way, any inefficiency at the first pulley is compounded throughout the system, so you want your most efficient pulley closest to the pulling force (that’s you).
For a 3:1 (below), your pull is closest to the travelling pulley, so that’s where the good pulley should go.
For you engineers and physics folks out there, an Alpinesavvy fan on Instagram (@jared_vilhauer who's way smarter at this stuff than I am) calculated that:
If you have a 50% efficient carabiner on the tractor, your real world mechanical advantage is 1.95.
if you had a 90% efficient pulley on the tractor, your real world mechanical advantage is 2.35
If you want to take a deeper dive into this, here's a nice video from The Rope Access Channel that walks you through each step. His example shows a redirect off the anchor (good practice if you need to lift the load vertically instead of horizontally) but the principle is the same. If you put the pulley closest to the load from the pulling force (aka you) that’s optimal.
image credit : the rope access channel screen grab from https://www.youtube.com/watch?v=sIMFvf_E5Y8
A lot of folks think the pulley always should go on the moving part of the load to gain easiest pull, but this is not always true. Below, in the 2:1 with a redirect, the pulley should go on the anchor. Again, it’s because the anchor is closest to where you’re actually pulling on the rope.
This may seem a little counterintuitive (it was to me!), but it's easy to set up a test and prove it to yourself. Get a pulley, a carabiner, a rope, something heavy, and an anchor point. Set up each way and notice the pulling force needed in each set up. In this case, a pulley on the anchor is better.
Confession: this did not intuitively make sense to me, so I did a little observational study to prove it to myself.
I set up a 2 to 1 system, redirected through a top anchor point, as in the diagram above. I had a 10 pound barbell weight, and attached an inexpensive spring scale to the pulling strand. I pulled at a slow steady rate, and noted the most common whole number reading on the digital scale while I was pulling.
2:1 - pulley on ANCHOR, carabiner on load: 8.5 lbs. of force needed
2:1 - pulley on LOAD, carabiner on anchor: 11.3 lbs. of force needed
2:1 - pulley on BOTH anchor and load: 8.2 lbs. of force needed
Clearly, putting the pulley on the anchor is the best approach. I almost didn’t need a pulley on the load, as the force needed with a pulley or a carabiner on the load was almost the same.
