Mechanical Advantage
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Do you have a big load that you need to move a short distance? Here's one crafty way to do it: the stirrup hoist. This may not be the most efficient method, but it's quick and simple.
Do you have a big load that you need to move a short distance? Here's one crafty way to do it: the big waller's trick of the "far end haul". aka 2:1 redirected haul. (I learned this from big wall expert Mark Hudon, thanks Mark!)
With nothing more than a cordelette and two carabiners, the “alpine block and tackle” creates a bit of mechanical advantage that can help you move a large load a short distance.
Do those pictures in the rock rescue book of a 5 :1 rescue system leave you scratching your head? Yeah, me too. These posts, written for the math-challenged, takes a deep dive into the theory and application of mechanical advantage systems for climbers.
Meet your new climbing partner, Sticky! Let’s start with the basics, a straight 1:1 pull. Then, we’ll add some components that make it into an MA system with progress capture.
Knowing how to set up a 3:1 mechanical advantage Z drag system is fundamental to rope rescue. However, it's a lot easier to remember if you follow a sequence of steps. Here’s a photo walk through of how to set up a Z drag.
Alpine climbers and big wall climbers have different requirements when it comes to MA systems. Here’s a summary.
A few of the more common questions about MA systems and gear are covered here.
Say you need to set up a mechanical advantage system, and you only have one pulley. Your choice of where to put it can make a difference in your ease of hauling. Sometimes this will be on the load, and other times it might be on the anchor.
We often have to improvise on gear for alpine rescue scenarios, but carabiners really do suck for hauling. This post may convince you to carry a pulley more often.
The progress capture / ratchet is a critical part of a hauling system. There are lots of devices you can use, and they vary greatly in terms of weight, cost, and most importantly, friction.
Here are some test results from various combinations or pulleys and carabiners for 3:1 and 2:1 MA systems. Some things were as expected, but I got a few surprises.
You have lots of options for pulleys, carabiners and ratchet mechanisms. Some are wildly less efficient than others. There are two you should really avoid using.
No, it’s not a trick question. MA systems can be a definite benefit, but in the end, you’ve done the same amount of work.
Does an MA system always increase the load on the anchor? Usually yes, but sometimes no. Yes, it can be a bit confusing. This post will clarify.
Getting into slightly more advanced MA topics - the differences between simple, compound and complex pulley systems.
Here’s how to calculate the actual MA of a given pulley system.
Pulley diameter and rope stretch do affect your hauling efficiency. It’s more relevant to mountain rescue teams and big wall climbers than to alpine climbers.
Once you have a 2:1 and a 3:1 mechanical advantage system dialed, It's easy to combine them and get a 6:1. Here are two step-by-step examples how to rig these with a minimum of equipment.
You can tie a Z drag in your sleep. You bring a pulley to the rock gym. You are a Mechanical Advantage ninja. You’re ready for the bug guns - bring on the 9:1!
Think you have a good understanding of a simple 1:1 and 2:1 mechanical advantage systems? Well, it turns out there's one very interesting variable: who’s doing the pulling? If you, (i.e, the load) are lifting yourself, the mechanical advantage increases! No, this is not very intuitive, and yes it is helpful for climbers. (Thanks to ropelab.com.au for the diagrams.)
When hauling on a big wall a 1:1 mechanical advantage system might need a boost, if your bag gets hung up or is dragging on a slab. Here's a quick way to increase your pulling power to a 3:1.
On a longer big wall, with bigger loads, using mechanical advantage to lift your haul bags can be extremely helpful. Here's a deep dive into the 2 to 1 hauling system.
Sure, a svelte progress capture pulley in a hauling system (such as a Petzl Micro Traxion) is great. But if you don't have one, a quick link, captive eye carabiner, or belay device can help keep your prusik loop in place in a hauling system. And let's not forget the big wall favorite, an ascender.
Here's a link to a very cool online mechanical advantage calculator! Choose your rigging method, choose your components, choose your load, click a button, and you instantly see all of the different forces in the different legs of your rigging system. Courtesy of the New Zealand-based guiding company, alpinerecreation.com.
A good general rule: use the least amount of mechanical advantage (MA) that you can to get the job done. Adding additional pulleys and ropes grabs also introduces more friction. In some cases, what you think is giving you extra MA may actually be worse than what you had before.
Mechanical advantage (MA) systems have been described as like a blind date: what’s promised is always better than what's delivered. There can be a significant difference between theoretical, calculated, and real-world mechanical advantage. Learn what these are and see some examples.
After you have the basics of a 2:1, 3:1 and 6:1 hauling system dialed, rope geeks and mechanical advantage fans might want to learn some more esoteric rigging. Here's one of them, the 3:1 Spanish Burton. It lets you pull down, instead of up, which could be helpful in a vertical haul. Practice with it, it's fun!