If you Build it, It will Fall! - Mechanical Advantage in the Tree Industry.
In our industry, performing tasks efficiently and safely often involves overcoming the challenges posed by the size and weight of trees and in some instances, tree sections. Mechanical Advantage (MA) refers to the amplification of force achieved by using tools and systems that distribute the load and leverage the principle of physics. This is what allows us to accomplish great feats with such small crews. The purpose of this blog is to spark interest into mechanical advantage systems (if you don’t already apply it), the tools required, both simple and compound systems.
Simple Mechanical Advantage Systems
Well, simple systems can be defined as systems where one rope is routed between one or more pulleys on the anchor and the load. You will effectively double the force you exert, making life easier! What this means; hypothetically, if you were to input 100 lbs. of force into a 2:1, the load should experience 200 lbs. of force – halving the effort required on your part.
- Easy to set up and use.
- Provides a significant boost in lifting or pulling power.
- Ideal for straightforward tasks requiring a moderate MA.
- Limited increase in efficiency compared to more complex systems.
- May not be suitable for extremely heavy loads or complex scenarios.
Compound Mechanical Advantage Systems
When we are faced with more challenging scenarios, such as hoisting logs or felling leaners; where machinery can’t get to, this can be interesting yet fun to set up. In a compound system, simple setups are taken a step further by stacking one simple system onto another simple system, and we’ll then multiply the two systems to get our resulting MA. Doing this will create multiple friction points that amplify the force applied. It’s MA on steroids!
- Offers a higher mechanical advantage compared to simple systems.
- Handles heavier loads and more complex tasks.
- Maintains a manageable level of rope travel for each pull.
- Requires more hardware, which may not be readily available.
- Having appropriate anchor points. You will create MASSIVE force!
- May take practice to assemble.
- Pulling a lot of rope.
There is another… Piggyback MA!
This to me, is the crème de la crème of MA systems! Piggyback systems are MA on a haul line. For example, the tree being felled will have the tag line on it and onto it, another pre-rigged MA system is connected to the tag line via prusik. It may be helpful if you rig up a form of progress capture onto the tag line, in the event the system needs to be advanced further onto the rope or lowered. However, in our world, lowering with MA is almost non-existent.
Sometimes, determining the MA of a system isn’t as obvious as you would like it to be. At times, systems using multiple carabiners, ropes, and at times, it will depend which way the user is pulling from. This can heavily dictate the MA outcome. A simple way to calculate how much MA has been created is to use the T-System. It works great to help decipher simple and compound systems; however, it may get dicey when trying to figure out these elaborate systems.
What tools are required?
There are a multitude of ways in accomplishing MA systems from only using rope to including carabiners, prusiks, and pulleys. It is important to note that when using a rope-on-rope MA system, you run a high risk of melting the rope due to the amount of friction that will be applied and that is why the additional use of hardware is recommended. One thing to understand with pulleys; it does not create a true “friction free” system. There will still be some efficiency loss whether at the pulley itself or lost within the rope traveling through the system.
Building a SIMPLE MA system.
Quick and easy SIMPLE systems to build include 2:1 and 3:1.
2:1 includes the following:
- Anchor your haul line onto the anchor itself.
- Run the haul line up and attach it via pulley onto the load being shifted.
- Last step, get pulling.
3:1 MA or known to some as, Z-Rigs
- Begin by tagging the load with a haul line.
- Run the rope back to the suitable anchor and pass it through a pulley (you may add a progress capture prusik if desired).
- Attach a prusik and pulley combo up onto the leg of rope tagged onto the load.
- Rope goes through the newly attached pulley.
- Voila, you’ve just created a Z-Rig!
Compound systems can be tricky to build at first, but I will attempt to break down a compound 6:1 right here:
- Follow the steps above and build yourself a quick 3:1.
- In this instance, the standing leg coming out of the pulley is not long enough, so we’ll attach it to a carabiner and pulley combo.
- We’ll bring in another rope and with this new rope, we’ll anchor an end to our anchor point.
- Follow that by running this new rope through the last pulley we’ve attached.
The end result gives you a compound 6:1. When systems like this become stacked, we calculate the total MA by multiplying 2:1 and 3:1. Ultimately giving us the 6:1.
I’ll leave you with this question:
Our standard moving rope system; is it a 2:1 or not? In the world of rescue, the rope is terminated at an anchor point and then gone through the pulley. In our climbing world, we as the climbers are both the load and anchor point. So, what does that mean there?! Let us know your thoughts.