I recently came across this clever online tool from alpinerecreation.com, a New Zealand based guiding company.

It’s a mechanical advantage calculator, very cool!

This is an excellent way to instantly see some of the forces involved with different rigging methods, and how using a carabiner rather than a pulley can change the efficiency of your system.

(Works fine on a mobile phone but it's easier to see the big picture on a wider computer screen.)

• Choose your hauling system (2:1. 3:1, 5:1, 6:1, etc.)

• Choose your components (Micro Traxion, rescue pulley, large carabiner, small carabiner, etc.)

• Choose your load (default is 100 kg)

• Choose your units (percentage of load, kg, or kN)

Press “Calculate” and it gives you values and forces all the way through the system!

Check it out here.

Here’s a screen grab showing values for a 3:1 Z drag, using a Micro Traxion as the progress capture and a good quality pulley on the “tractor”.