Alpine Tips
Load transfer - The 2:1 redirected haul
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!)
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This is part of a series of articles that cover methods to move a large load a short distance, typically to unweight an anchor.
I learned this trick from big wall expert Mark Hudon, thanks Mark!
You may find yourself in a climbing situation where you need to transfer a BIG load from one anchor point to another.
Beginner big wall climbers, you know what I'm talking about; you clipped the haul bag in the wrong spot and it needs to get moved, whoops! (I’m an expert on this particular mistake; I probably did it five times on my first wall . . .)
Maybe a rescue situation (which you’re hopefully never in) where you need to lift the weight of your uncooperative partner off of the anchor to continue rappelling.
How can you do this the SMART way?
Brute force powerlifting is probably not going to cut it. It's much smarter to use a little mechanical advantage to make this happen. Work smart, not hard!
Here's one method: a redirected 2:1 haul with a progress capture pulley. In the big wall world this is known as the “far end haul”; here's an article on that.
The steps here might appear complicated when you see them the first time, but as soon as you give it a try you'll learn how easy it is.
Look through the step-by-step photos below and then watch a how-to video at the bottom.
You have a big load on the right anchor, and you need to move it to the left anchor. How do you do this the smart way?
Here’s a step-by-step sequence, with a tutorial video at the bottom.
Clip some cord or rope to the anchor.
Clip your progress capture pulley such as a Petzl Traxion, onto the rope is shown. (Remember to clip it “teeth to tail”, so the “teeth” on the device point to the “tail” side that you’re going to pull.)
Clip the Traxion onto the load.
Add a redirect to the anchor. A pulley is good here if you have it. In this example, I’m using the excellent Petzl Rollclip.
(In this example I clipped the redirect on to the anchor on the right. It also works fine if you clip it to the anchor on the left.)
Now you're ready to pull.
Put the rope or cord through a Grigri or a Munter hitch on your harness.
Pull DOWN with your body weight.
As you do this, you’re raising the load with a 2:1 mechanical advantage, and the Traxion pulley captures your progress. Nice!
With the high-efficiency Traxion on the load and the Rollclip/pulley on the redirect, your loss of pulling force due to friction is minimized.
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Load transfer: The alpine block and tackle
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.
Premium Members can read the entire article here:
This is part of a series of articles that cover methods to move a large load a short distance, typically to unweight an anchor.
If you tie your cordelette “bunny ears” style, as I recommend in this Tip, you can use it to make a low-tech block and tackle system. #CraftyRopeTrick for sure!
(History side note: The term “block” comes from the wooden blocks that were originally used on ships to raise heavy sails, and the “tackle” refers to the ropes/rigging running between the blocks.)
Climbers typically think that mechanical advantage systems only come into play in a rescue-type scenario. But there are some other situations where they can come in handy.
When might you want to use an alpine block and tackle?
In general, to move a large load a very short distance.
Maybe you're in some other kind of rescue scenario, and you need to momentarily lift a load off of a carabiner an inch or two to unclip something.
Maybe you're on a big wall climb, you screwed up your rigging somehow, and you need to lift your haul bag a few inches to get it unclipped. (Note, if you use a docking cord to attach your haul bag to the anchor, you should never have this problem.)
You have a strand of rope with a weighted knot, and you need to unweight the rope so you can untie the knot. To do this, put prusik loops above and below the knot, and rig the block and tackle between the two prusiks. See image below.
In the example shown in the video below, you can transfer or share the load in a crevasse rescue off a sketchy initial gear placement to a stronger second placement.
Want to see my test results for the real world mechanical advantage of this rigging?
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Introduction to MA systems
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.
First off, thanks to some Very Bright People who helped with these posts. High fives to Barry O’Mahony, Bryan Hall (with Rose City Ropes) Deling Ren, and Derek Castonguay. Thanks, friends!
I'm busy and I have a short attention span. What's the takeaway?
Start with learning 2:1 and a 3:1 until you can build them with your eyes closed. Every other fancy system is really just a combination of these.
Real world mechanical advantage will always be less than theoretical mechanical advantage. Sometimes a lot less - that “3:1” is probably more like at 2:1.
Use pulleys instead of carabiners when possible.
Redirecting the pull adds friction. Don't do it unless you need to.
A pulley on the anchor only serves to change the direction of pull. A pulley on the load or the load strand creates mechanical advantage.
The efficiency of ratchets is worse than you may think.
Redirecting the pull through the anchor magnifies your pulling effort on that redirect point.
Mechanical advantage systems can increase forces on the anchor.
Static ropes are more efficient than dynamic ropes.
A pulley with a larger wheel is slightly more efficient than a pulley with a smaller wheel.
Don't use more mechanical advantage than you need to get the job done.
Alpine climbers and big wall climbers have different needs and different systems
These blog posts are mostly arranged with easier topics at the top and more advanced topics closer to the bottom.
Got some time and a longer attention span and really want to learn this stuff?
Good, let's get started.
I'll always remember my first encounter with pulleys. In the rural area where I grew up, we had a neighbor named Ray, who was always messing around with cars. One day my dad said, “Let's go visit Ray tomorrow morning, I think he has something special to show us.”
The next day we walk over to Ray's house. He’s elbow deep in an old Chevy, that’s parked under an oak tree with a stout branch. I see some ropes going back-and-forth between the tree branch and the car, but that doesn't mean anything to me. After a few minutes. Ray hands me a rope end and says, “OK, start pulling.” I pull hand over hand on the rope . . . and watch in absolute amazement as my 8 year old arms lift the entire engine out of the car! The magic of pulleys had me feeling, for a brief moment, like a superhero.
Mechanical advantage (mostly referred to from here on as MA) which rather magically magnifies your pulling power, is one of the wonders of human ingenuity. Something as simple as running a rope back and forth between an anchor point and a load can somehow give you the power to lift a load many times your own body weight.
Mechanical advantage in various forms was a key component of building the Egyptian pyramids. Sliding a block up a ramp is shown below is a form of mechanical advantage, because you’re moving the load several horizontal meters and only one vertical one, which means it requires less force to move.
Systems of pulleys are used on modern cranes to lift amazingly large loads.
Applications of mechanical advantage have been used for many centuries in all kinds of different clever ways!
This series of posts takes a deep dive into MA, how it works, and how it can be applied to climbing situations. The goal here is for anyone reading this, especially non-engineering people, is to start simple, get a bit more esoteric, and by the end have a complete and solid understanding of MA pulley systems and how they apply to climbing. If you make through all these posts, you’ll be an expert!
Knowledge of mechanical advantage systems is not helpful only for climbers. White water rafters and kayakers use similar rescue systems, and this series of posts will be helpful for them as well.
Note that this post is NOT a rehash of the specifics of how to perform alpine rescues or big wall hauling. Those topics are already well described in many other places on the web and in print.
Moving rice bags: a way to think about MA
Imagine you work at a grocery store. One morning a delivery truck drops off a pallet, on which are 10 bags of rice. Each bag weighs 20 pounds, for a total of 200 pounds.
Your job is move the rice bags from the loading dock into the store. How do you want to do this?
If you’re feeling pretty strong, make a single trip: deadlift 200 pounds, and slowly walk it into the store. We could call this a 1:1, lifting and moving the entire weight once.
If you’re not feeling strong (and maybe getting paid by the hour) you could take one rice bag at a time and leisurely walk it into the store, taking 10 trips to move all 10 bags. It takes very little effort to lift each bag, but you have to do it 10 times. We could call this a 10:1.
Or, a more practical approach may be somewhere in the middle. You could take, say, two bags at a time, a manageable 40 pounds, and make five trips to carry the 10 bags into the store. We could call this a 5:1.
In the end, all of the bags are moved from point A to point B. You haven’t magically made the 200 pound load any lighter, moving the 10 bags still took the same amount of “work”, but you simply changed the time and distance involved to move the load. Is one “easier” than another? No.
The basic question is, would you rather move 200 pounds one time, 20 pounds ten times, or maybe 40 pounds five times? There’s not one correct answer.
Let's start with some definitions.
Mechanical advantage, or MA: This is the magnification of your pulling effort. It's expressed as a ratio, such as 2:1, 3:1, and is pronounced “2 to 1” and “3 to 1”. The first number is the force applied to the load, and the second number, which is always one, is the effort that you apply to the rope. For example, in a theoretical 2:1 system, if you pull with 100 pounds, you can lift a 200 pound load. A 3:1 system with a 100 pound pull let’s you lift 300 pounds. Magic!
Theoretical (aka “ideal”) vs Real World (aka “actual”)MA: On paper, in a frictionless world with perfect pulleys and ropes that don't stretch, MA systems work as advertised. But in the real world, not so much. Mostly due to friction, real world, or actual MA will always be less than theoretical, or ideal MA. (Meaning, that theoretical 3:1 may be more like a 1.7:1, ouch!)
Efficiency: Closely related to MA is efficiency. Think of efficiency as: how much of your effort is actually getting through to the load to do some useful work? High efficiency is good, because it means you need to do less work. (And let's face it, most of us are lazy.) In the real world, haul system efficiency is affected by a wide range of things, such as stretch of the rope under load, the quality of your pulleys, rubbing and twisting of the rope, how often you need to reset your hauling system, and a few other quirky variables.
Friction: the main and messy variable that takes nice “theoretical” MA and turns it into “real world” MA. With a 2:1 system, in theory a 100 pound effort can lift a 200 pound load. But in the real world, friction will always mean you will be moving less than 200 pounds. Depending on your choice of gear, it can sadly be a LOT less. In climbing, friction mostly comes from the rope bending to go through a pulley or carabiner, or the rope rubbing on a rock ledge or a crevasse lip. Friction is not our friend, and we want to try to minimize it whenever possible.
Fixed pulley: a pulley/carabiner that’s attached to the anchor. This pulley does not move, and serves only to change the direction of pull. It does not create MA.
Moveable pulley: aka travelling or “tractor” pulley/carabiner. This is attached in some way to the load or the load strand. This pulley moves as you pull the rope. It changes the direction of pull AND creates MA.
Progress capture: aka ratchet. If you pull on a load, a progress capture means the load won’t slip back once you stop pulling. A progress capture in climbing is typically either a simple prusik knot or a pulley that is combined with a rope grabbing mechanism. These pulleys, such as Petzl “Traxion” series, are expensive, but very handy. Progress capturing pulleys are optional for alpine climbing but mandatory for big wall hauling. More on ratchets in a later post.
Below are two examples of a progress capture - the humble prusik and the Petzl Mini Traxion (shown open to illustrate rope grabbing teeth.)
progress capture: Petzl pulley and sterling hollow block tied as 3 wrap prusik.
progress capture: petzl mini traxion
Overview of a simple pulley system
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.
Let's start simple.
I don't know about you, but when I start looking at diagrams of complicated pulley systems and 5:1 rescue setups, my eyes get crossed and my brain starts to fog. Good news is, we don’t need to analyze a 5:1. At least not right now. Let’s break this down by starting at the beginning and then working up to a simple MA system, so you can really see how this works.
The basic 1:1 pull
Sticky the climber needs to haul a 100 pound load up to the ledge. Sticky ties a rope onto the load, and starts pulling. To even budge it off the ground, Sticky needs to pull up with 100 pounds of effort. Sticky pulls 1 foot of rope, and the load rises 1 foot. Sticky has no mechanical advantage or progress capturing, so Sticky’s arms get tired pretty fast!
In this case, it's probably not a good system. But in other situations, it might work just fine. Got a crevasse rescue with five people on top ready to pull? Great! Put prusiks on the rope for everybody, have them clip in, and start pulling, ideally with their legs and bodyweight. Probably no need for anything fancier than this.
Bluehat thinks, “Hmm, how about clip a carabiner to that bolt, and clip in the rope? That way, I can pull DOWN with my bodyweight instead of lifting UP with my arms, and I won't get so tired. That should be easier, right?”
The 1:1 pull with a redirect carabiner
Does Bluehat gain any MA with this setup? No. He changed the direction of pull, but because the direction change is on the fixed anchor, he did not gain any MA. He’s still pulling a 1:1, just like before, just with the rope now moving down instead of up. He pulls 1 foot of rope, and the load rises 1 foot. This carabiner on the anchor is called a “redirect”, because it, umm, redirects your direction of pull.
Does he get an easier pull? Maybe. He can now use gravity and pull down using bodyweight rather than lifting up with his muscles. Pulling down is usually easier than pulling up! But the redirect adds a lot of friction. By running the rope through a carabiner, which is only about 50% efficient, he'll have to pull down with 150 pounds of force to move the 100 pound load.
Which is better, 100 pounds lifting straight up, using your arm muscles, or 150 pounds, pulling down, using your bodyweight? There's really no right answer. It depends on how far you need to move the load, your weight, and your strength. (Personally, I'll take 150 pounds with the redirect pulling down, thank you very much.)
Does he need a bomber anchor for the redirect? Yes! When Bluehat is pulling, the force on the anchor is approximately twice the force they’re applying to the rope, or about 300 lbs. Which introduces a good general rule of thumb: a redirect on the anchor increase the load on the anchor.
The 1:1 pull with a redirect carabiner and progress capture prusik
Bluehat thinks, “Well, it is easier pulling down with my bodyweight, but if I ever let go, this load is going to zing all the way to the ground again. How about I put a prusik on the load strand so I can take a rest?”
Excellent idea! This is known as a progress capture (aka “ratchet”). It allows the load to move up, but whenever Bluehat wants to let go and rest, the prusik keeps the load from sliding back down. (If you want to get fancy, you could use a progress capture pulley here, such as Petzl Traxion.)
The 2:1 pull
Bluehat thinks, “OK, time to start working smart instead of working hard!” He clips one end of the rope to the anchor, puts a pulley on the 100 lb. load, runs the rope through the pulley, and starts hauling. Now he’s getting somewhere!
Does Bluehat gain any MA with this setup? YES! He’s now pulling with a 2:1 mechanical advantage. Look how the load is distributed on the rope. 50 pounds goes to the anchor, and 50 pounds goes to him. So, if he pulls with 50 pounds of force, the load will rise! He has to pull 2 feet of rope to move the load 1 foot.
Does he get an easier pull? Well, it depends how you look at it. In theory, he only has to pull with 50 pounds of force to move the load, which is good. But, he needs to pull twice as much rope, which is not so good. In the end, he's doing the same amount of “work”. Would you rather lift 100 pounds 10 times, or 50 pounds 20 times? In the end you’ve still moved 1,000 total pounds, it's all the same.
Here's another way to think about it: work equals force times distance. You're doing the same amount of work in the end, lifting a given load the required distance. But with a mechanical advantage system, you use a lower force to move the load over a longer distance.
How’s he doing for efficiency? Great! By using a quality pulley on the load, he can lift the load with much less effort. Way better than the carabiner with a 1:1 redirect.
The 2:1 pull with redirect and progress capture prusik
Bluehat thinks, “Well, this is definitely easier to pull, but my arms are still getting tired. Let's put a redirect on the anchor, and a prusik on the load strand.”
Now we're getting somewhere. He’s lifting with 2:1 MA, , and added a ratchet prusik so he can take a break whenever he needs to without dropping the load. Nice!
This, right here, is the foundation of mechanical advantage systems. All the fancy stuff in the rock or crevasse rescue books that makes you go cross-eyed? It's all just adding and stacking additional redirects and pulleys in different variations on top of pretty much what we just saw.
Now, the above diagrams might appear to be overly simplistic. But if we break them down, we can learn some important principles that apply to any flavor of simple or compound pulley systems.
Changing the direction of pull at the anchor does NOT add mechanical advantage.
Changing the direction of pull at the load (or the load strand) DOES add mechanical advantage.
Even if a change of direction at the anchor does add friction, it might make your pull easier, depending on your own personal strength, body weight, and the weight of the load you need to move.
A redirect on the anchor increase forces on the anchor. Be sure your anchor can handle this.
Try to minimize friction at every change of direction by using a pulley rather than a carabiner whenever possible.
Adding a progress capture / ratchet means your load will not slide back down if you stop pulling.
In the end, the “work” you do is the same with an MA system. You move the same amount of weight over the same distance. So, in a sense it's not necessarily “easier” to move the load all the way up, you just get to pull less weight on each stroke.
A 3:1 “Z” drag, step by step
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.
The “Z” drag (so named because the rope looks like the letter “Z” if you turn your head sideways) which gives you a theoretical 3:1 mechanical advantage, is one of the fundamental setups of crevasse and rock rescue. After you've done it a few times, most people get the hang of it. But if you haven't rigged it in a while, or if you're doing it under the stress of a real rescue situation, setting it up efficiently and correctly can be a challenge. (I’ve seen some quite experienced climbers have a complete brain fade trying to do this if they’re out of practice . . .)
Here's a step-by-step walk-through. Hopefully this will help if you're new to rope rescue, or to dust off this skill if it’s been awhile. So get a rope, 2 prusiks, a few carabiners and a pulley if you have it, and follow along.
Note 1: This shows the basic mechanics of how a Z drag is set up, not all the possible nuances of gear and technique. Prusik minding and progress capturing pulleys, rope grabs, backup knots and releasable hitches, and other fancy rope tricks can be added after you know this foundation inside and out.
Note 2: Don't pull furniture around inside your house as it's tough on the floor and carpet, ask me how I know this . . .
Step 1 - Construct a bomber anchor. Add a locking carabiner. Clip this carabiner to the rope with the load. You now have a 1:1 system (zero mechanical advantage) with the rope redirected.
Step 2 - Add a “capture” prusik on the load strand of the rope, and clip this prusik to the anchor. (This prusik loop “captures” your pulling progress, holding the load if you let go of the rope.)
Step 2A - The way it's set up now, when you haul on the rope, the prusik will pull through your carabiner. Not good. There are a few ways to prevent this. One is to add a quick link, as shown below, which should block the prusik from sliding through. The effectiveness of this depends on the few variables such as size of your quick link, and diameter and grip-tion of rope and prusik cord. Give it a try and see how it works. (You can get quick links that are actually CE rated for climbing from CAMP, discussed here.)
Another way is to have a second person “mind the prusik”, keeping it loose when you're pulling, but letting it go tight on the rope to hold the load when you stop pulling.
If you have a fancy and somewhat expensive “prusik minding pulley”, this is where you’d put it.
(And yes, clever reader, I know the trick of adding a tube belay device here, we're not covering that today.)
Step 3 - Add a second prusik, called a “travelling” prusik, onto the load strand of the rope. It's called the “travelling” prusik, because it moves when you pull. If your prusik cord is a little long, like the one I have here, tie an overhand knot to shorten it up. Shorter is better.
Step 4 - Put the free end of the rope through a pulley, clip a carabiner to the pulley, and clip that carabiner onto the travelling prusik.
If you don't have a pulley, use a carabiner here. A pulley is better. If you have only one pulley, put it on the travelling prusik to increase your hauling efficiency.
Sweet, you now have a 3:1 and you’re ready to pull! Pull on the rope until your load is where you need it, or until the travelling pulley touches the anchor. If this happens and you need to pull some more, set the capture prusik to be sure it can hold the load, and then reset the travelling prusik by sliding it as far as you can down the rope toward the load. Continue pulling.
Alpine vs. big wall - different needs in MA systems
Alpine climbers and big wall climbers have different requirements when it comes to MA systems. Here’s a summary.
In general, there are two basic user groups for MA in climbing. They each have distinct needs and equipment.
The first one, for rock/ice and glacier climbing, involves a rescue situation. Here, you typically need to haul a big load a single time for a short distance with improvised materials, the size, bulk and weight of gear are important factors, and you may likely be using a more complicated mechanical advantage system, like a 3:1 or 5:1, to raise your patient. It’s also unexpected and stressful, meaning you may have to rig a more complex haul with improvised materials, quickly, without much practice.
Big wall climbing can also involve hauling big loads. But instead of 30 feet, you’re doing it for maybe 3,000 feet! Bulk, weight, and cost of equipment are factors, but not nearly as important as in alpine climbing. You are unlikely to be doing a 3:1 or greater haul, 2:1 is typically all that’s needed even for honker haul bags. And, because you are repeating the same movement so many times, you’re willing to take some time and invest in a perfectly dialed system that uses more expensive and slightly heavier gear, if it increases your pulling efficiency even a tiny bit. To summarize:
In alpine climbing . . .
You start your climb not knowing if you will need to haul (and hoping you won’t!)
Need understanding of various MA systems, 2:1, 3:1, 5:1, etc.
Probably won’t have the exact right tools for the job, creative gear improvisation may be required
Weight and cost of gear may dictate what you choose to carry
Usually need to move a load only a short distance, so highly efficient systems are generally not so important
In big wall climbing . . .
You start the climb knowing you will have to haul
Typically only using 2:1 MA, more MA not required
Carrying the exact right tools for the job is a priority, even if they are expensive, bulky, and weigh more
You are moving a heavy load for a very long distance, so well practiced and efficient systems becomes very important
A few basic questions and answers about MA systems
A few of the more common questions about MA systems and gear are covered here.
When I start looking at some of the more crazy pulley diagrams of 5:1, 6:1, 9:1 . . . my eyes glaze over. As a climber, what's the most basic system(s) I need to know?
Learn how to do a 2:1 and a 3:1 pretty much with your eyes closed. These are the foundation systems that are used most in rescue and hauling scenarios. Any system that creates greater MA than a 3:1 is just a combination(s) of 2:1 and 3:1. Once you have these dialed, you can play around with combining them in various way to make a 5:1 or maybe a 6:1. That should be everything you should ever need for a rescue scenario. Learn these basics first and don't get confused by the fancier stuff.
Note that it’s not likely you’ll be able to lift someone just with a 3:1 unless they are actively assisting. To be really sufficient for various rescue scenarios, add a 5:1 or 6:1 to your engrained memory. Here’s a great way to make a 6:1, for example.
The good thing is, you can practice these at first on the floor and in the comfort of your warm, dry house. But then, please go try them in a more realistic setting.
What are some real world climbing situations where I need to know this stuff?
Alpine climbing - In a crevasse rescue, you may need a 2:1, 3:1 or even 6:1. Or, perhaps various rock rescue scenarios where you might need to haul your second past a difficult move or two with a 3:1, and less commonly, setting up an “alpine block and tackle”, which can be a 4:1 or a 6:1 theoretical MA, which we cover in this tip here.
Big wall climbing - You’ve got two big honker haul bags for you and your partner to spend a week on El Capitan. The total load is going to be well over 200 pounds, and is going to absolutely suck to haul 1:1. Time to rig a 2:1 haul system. The scope of setting this up properly is a complicated topic and is covered in a separate post here.
I don’t quite understand the math around pulley efficiency. Can you explain that?
Sure thing. One way to think about it is how different pulley efficiencies determine the effort needed to lift a load. Let’s use 100 pounds as a nice round number.
The table below pretty much spells it out.
What do we notice? With high pulley efficiencies of 70 to 90%, you’re not going to notice much real world difference when lifting a load. When pulleys start to fall below about 60%, you’re definitely going to start noticing a difference. If any component in your hauling system is much below 50% efficient, you need to ask yourself why you’re using it at all.
I don’t quite get how a redirect increases force on the anchor in the real world. Can you explain that?
Sure thing. Say our friend Sticky decides to raise her 100 pound load through the carabiner redirected through an anchor point. The carabiner is roughly 50% efficient. From the table directly above, we can see that for her to lift 100 pounds, she needs to pull down with a force of 200 pounds. That force gets applied to the strand of rope she’s pulling. At the same time, the 100 pound load is weighting the other strand of rope. So together, her pulling force of 200 pounds plus the 100 pound load add up to be a 300 pound load on the anchor.
Now, let's say she has a pulley that's 80% efficient, and she runs her load through that instead. From the table above, we can see that she would need to pull with 125 pounds of force. We add this to the 100 on the other side, and get a total of 225 pounds on the anchor. Hopefully this convinces you to use a pulley whenever possible!
(I did this myself with a 10 pound barbell weight, a spring scale hanging from the ceiling, and a 9 mm climbing rope. Sure enough, set up exactly like below, it took 20 pounds of pull to lift the 10 pound barbell plate off the ground.)
If a 9:1 is easier to pull than a 3:1, why don’t we use a 9:1 for everything?
Well, first try pulling with the 3:1 that you already have set up. If that's getting the job done, don't make it more complicated. Remember, every additional redirect and pulley that you add increases friction and decreases the real world MA. It also increases the amount of rope you have to pull through the system to raise your load, requires more gear like carabiners, prusiks and pulleys, and it may increase how often you need to reset the haul pulley. It can even add some more unexpected weird variables, like ropes twisting, ropes rubbing on each other, and prusiks slipping. Remember the law of diminishing returns from that long ago economics class; adding more input does not always get you a good return on the output.
A good rule of thumb: use the minimal mechanical advantage system that you can to get the job done. The best system is not necessarily the one which creates the greatest MA.
How about something like a DMM Revolver carabiner, that has a little wheel in it, or the Petzl “ultra legere” orange plastic wheel thing. Can I use these instead of a pulley?
Probably not. The Revolver carabiner was really designed to minimize rope drag when lead climbing, not serve as a proper pulley in a block and tackle system. (My real world tests showed a Revolver carabiner was pretty much the same as a regular carabiner in hauling efficiency.) The legere I personally have found quite difficult to use in a crevasse rescue scenario, because the rope does not properly stay in place and wants to skip off of it at every opportunity. It also has it safe working load of only 1 kN, so that means it's appropriate for lifting your pack, but not a body. Get a real pulley (or two). See some real world test results here.
image: dmmclimbing.com
image pinterest.com/pin/369295238177239123/?lp=true
What kind of pulley should I get for crevasse / rock rescue?
There are two main types of pulleys, which you could refer to as fixed plate and swing plate. With the fixed plate pulley, the sides of the pulley look like a letter “U” and are made from a single piece of metal. Because of this wider shape, these can usually only be used with a oval or HMS belay carabiner. With the swing plate pulley, the two sides are separated, allowing one side to swing down to more easily insert the rope. The swing plate pulley is probably the most useful one to have for alpine rescue. The advantages are, it's easier to put the rope in, and it works with just about any kind of carabiner.
Having said that, it's usually better to use an oval shaped carabiner with a pulley if you can. If a D-shaped carabiner tilts the pulley off to one side, you're going to lose efficiency, because the pulley bearings will not be properly sharing the load.
image: https://smcgear.com/crx-pulley-orange.html
The American Alpine Institute recommends this model pulley for their glacier travel and crevasse rescue classes: the CRx, made especially for crevasse rescue. (“CR” Crevasse Rescue, get it?) It's a solid pulley, from the respected company SMC (Seattle Manufacturing Company), and best of all it's only about 15 bucks. I have one, it’s great.
Note that the wheel (aka sheave) in the CRx pulley is plastic, not metal. This makes it a hair lighter and less expensive, both of which are good for a lighter duty rescue pulley. But if you’re looking for a big wall hauling pulley, you want a larger diameter metal sheave with sealed bearings, both of which will increase your hauling efficiency, which is important when you're doing it 3000 times. More on big wall hauling systems and pulleys is in this post.
Petzl, SMC and CMC all make quality pulleys. Pretty much any small pulley by a name brand climbing company is going to work fine. You can find a lot of small inexpensive pulleys on Amazon; some of these are probably great, and some of them probably suck, so personally I'd stay away from those. There are ways to skimp on gear - rescue equipment is probably not a good one.
There is also a flavor of pulley called a “prusik minding” pulley, or as some manufacturers call it, a “PMP.” These pulleys have a wider faceplate on either side of the wheel, which is designed to keep the prusik from being sucked into the wheel during a crevasse rescue. If you're going to get one pulley for crevasse rescue, you very likely want to get a PMP. Like I said, don't skimp on rescue gear. PMPs vary a lot in price. That’s why this CRx is such a good deal.
Where to put the pulley?
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.
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.
Pulley vs. carabiner - What’s the difference?
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.
You may be wondering, does it really make that much difference if I use a pulley or a carabiner?
Short answer, it can make a lot of difference. Use pulleys whenever possible. We had a look at this above with the Sticky diagrams, but it's important to get this, so let's have a quick review.
Say you need to lift 100 pound load, with a 1:1 system redirected through a high-quality pulley which is 90% efficient, which is pretty typical for a standard rescue pulley. Here, you need to apply 111 pounds of pulling force to move the load. (The math for this is 100 divided by 0.9).
However, let's redirect that same 100 pound load through a carabiner, which has an efficiency of roughly 50%. Here, you need 200 pounds of pulling force to move the load. (The math for this is 100 divided by 0.5).
So, use a pulley and pull with 111 pounds, or use a carabiner and pull with 200 pounds? Easy choice!
Here’s a table of pulley efficiencies. You may have seen this in another post, but it’s important, so I’ll include it here again. This is for a 1:1 haul through a redirect point. (If that last sentence made no sense to you, read this post first.)
OK, so that's for 1:1 redirected pull. How about for a 3:1 hauling system?
Great question. Check out the series of four photos below.
Top left: the most efficient system, with 90% efficient pulleys. MA of about 2.7 to 1, about as good as it's ever going to get.
Top right, carabiner for progress capture, pulley on tractor. MA of about 2.4 to 1. Still not bad!
Bottom left, pulley for progress capture, carabiner on tractor. Disappointing MA of about 2 to 1.
Finally, bottom right, carabiners in both places. Lousy MA, about 1.8 to 1.
A few thoughts on this . . .
My calculations use a pulley efficiency of 90% and a carabiner deficiency of 50%. (Yes I rounded off in a couple of places, don't beat me up on the math.)
It's clear that having a pulley closest to the hand that is applying the pull is the best way to rig.
Many people think that you should always put the pulley closest to the load. That is obviously not true.
Here’s a chart takes a little deeper dive into this for different systems.
With an MA system of 3:1 and only use 50% efficient carabiners, your real world MA is going to be about 1.75:1, ouch! (Plus, you still have the dismal progress of a 3:1, with only 1 foot of lift for every 3 feet of pull, even though you're pulling harder than you should have to.)
In this case, you may be better off using a 2:1 with one good pulley than a 3:1 with carabiners! We can see from the chart that a 2:1 with 20% friction (i.e., a 80% efficient pulley) gives us an MA of 1.80:1. But, a 3:1 with carabiners gives us an MA of 1.75:1.
So, use real pulleys whenever possible.
image: https://roperescuetraining.com/physics_friction_raising.php
If you have to use a carabiner, which kind is best?
I’ve heard over the years that generally, a carabiner with round metal stock is is going to be more efficient than the new style “I-beam” construction with a narrower cross section. But is it really? if so, how much?
Here’s a Camp Nano carabiner on the left, and an old school Petzl Attache carabiner on the right.
What about the DMM Revolver carabiner?
The DMM revolver carabiner is a cleverly designed piece of gear. It’s a standard snapgate carabiner with a tiny roller wheel in the bottom. The Revolver carabiner was designed to minimize rope drag when lead climbing, not serve as a proper pulley in a block and tackle system.
Many people think (hope?) they can use a Revolver to lighten up their rescue kit, but unfortunately it doesn't work. I don't know precisely why, but I think the pulley wheel is so small that under any significant load, it's sort of compresses and you end up with an efficiency pretty much the same as a standard carabiner. I actually tested it and found about 50% efficiency.
If you want a proper combination carabiner and quality pulley, check the Petzl RollClip (or Edelrid Axiom). It has a more substantial pulley in the bottom and works as advertised under load. It’s not used much by recreational climbers, but it's common equipment for rigging and rescue professionals.
I couldn’t find any sort of formal testing online that showed this, so I decided to try a little observational study myself.
Components:
10 pound barbell weight
Digital spring scale (about $11, I used this one)
9 mm dynamic rope
Old style Petzl Attaché carabiner (rounded)
New style Camp Nano carabiner (I-beam)
brand new rescue pulley
I tied the barbell onto the end of the rope, ran the rope through the carabiner on a bolted anchor to get a 1:1 with a redirect, clove hitched another carabiner in the pull strand and clipped the spring pulley to the carabiner.
I tried to pull straight down in a slow steady haul, and noted the most common reading on the scale. Any force over 10 pounds shows the inefficiency of the system.
Force needed with rescue pulley (baseline): 13 lbs - 77% efficient
Force needed with rounded carabiner: 20 lbs - 50% efficient
Force needed with a “I-beam” carabiner: 23 lbs - 43% efficient
(Math: 10 / 13 = .77; 10 / 20 = .50, 10 /23 = .43)
So, the rounded Petzl carabiner gives a slightly easier haul. (Note, this result was spot on with the often stated 50% efficiency rating of carabiners.)
Would you notice that extra bit of inefficiency in the real world? I’m not sure. But, if you have the option to use a round stock carabiner over an I-beam type carabiner use the round stock. Every little bit helps, right?
(Also, just for fun, I rigged two identical Petzl Attache carabiner side by side. The force needed to lift these was just 21 pounds, basically the same as the single Petzl Attache carabiner. In this case, adding one more carabiner really did not change the friction one way or the other.)
Now, something that definitely ventures into engineering-land that is beyond the scope of my expertise is something called “coefficient of friction”, which is a technical way of measuring how “slippery” something is. From my limited reading on this, the coefficient of friction for steel is different than that of aluminum, so apparently a steel carabiner will offer less friction than an aluminum carabiner. I don’t have a steel carabiner or else I would’ve tested this, it would have been interesting.
So, in summary, use a pulley if you have one!
Progress capture options
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.
The progress capture (aka ratchet), is a critical part of a hauling system. It allows you to take your pulling tension off the rope to rest or reset, without the load sliding backward.
There are a few possibilities for the ratchet. Here are some common ones, listed in increasing order of cost and/or weight:
Garda hitch
prusik
plaquette style belay device (like a Black Diamond ATC Guide or Petzl Reverso)
Grigri
Petzl Traxion
Let’s have a look at the pros and cons of these.
Note: especially for crevasse rescue, it’s really important to practice these different ratchet systems in the real world. It’s one thing to have them work in your living room floor, it can be completely different to see how they work under a lot of tension with snow being jammed up inside them.
I measured the efficiencies of these systems and wrote about them here.
Garda hitch
Pros: free and weightless. (So far, so good!) Cons: even when it’s set up correctly the carabiners can get a little wonky and fail to lock up, so it’s not the most reliable system, in my opinion. Plus, it adds a HUGE amount of friction, making your haul a lot harder! Personally, I would maybe use the Garda hitch for some non-critical tasks like hauling up a backpack, but not in a rescue scenario unless it was really the only option. Read more on the Garda hitch here. (And yes, I know it’s best not to use screwgate lockers for a garda hitch, sorry about that in the photo . . .)
Prusik loop
The classic method, and one still often used by guides, rescue teams, fire departments, etc. Pros: inexpensive, lightweight, can be improvised out of almost any kind of sling material. Cons: If it’s cinched down hard on the rope, it can add friction to your pull. You always want the prusik to be loose when you’re pulling, but in the confusion and stress of a rescue this can be an easy step to overlook. Unless you have a prusik minding pulley, (also known with the great acronym of “PMP”), or an extra person sitting next to it with the unenviable title as “prusik minder”, or someone who’s coordinated enough to do both the hauling AND the prusik minding at once, the prusik can get sucked into the pulley and cause all kinds of problems. Plus, every time you slack off from pulling, unless someone slides the prusik back toward the load, the load is going to slide backwards the length and stretch of the prusik loop, which can mean when you reset your pulley you’re losing a foot or so of hard-earned lift. (Your partner stuck in the crevasse will NOT appreciate being a lowered a foot or two when this happens.)
An old-school Crafty Rope Trick (CRT): if you don’t have a prusik minding pulley or just a carabiner at the anchor: run the rope through a tube style belay device like an ATC before you clip it through the carabiner. The belay device keeps the prusik loop from getting pulled through the carabiner. It actually works surprisingly well, give it a try. See photo below.
Black Diamond ATC Guide
(or similar plaquette-style device). If you set these up in autolocking belay mode, the rope will slide through as you pull, but when you let go, will lock down immediately. Pros: no loss of progress when you stop pulling. If you’re already belaying your second from the ATC, it's very simple to set up a 3:1 left. Cons: An extra piece of gear you may not have with you, especially on a glacier climb.
I did some informal testing on this, and believe it or not, found it does not add any significant friction. This surprised me a lot, because when I tested the ATC simply as a redirect for 1:1 progress capture, it had a terrible efficiency of only about 15%, and I assumed this would also transfer over to doing at 3:1. Happily, it does not!
I tested this with both a 10 pound load and a 100 pound load. Real world mechanical advantage was the same in both cases: about 1.5 to 1. This is pretty much the same as using only carabiners and no progress capture at all.
I'm not entirely sure, but I think I know why this is happening. When you start to pull, you generate a little bit of slack at the ATC, and this slack means the rope passes through the ATC with minimal tension, so no extra friction. I am no engineer, and this is just one observational study, but it seems to me that’s why it works reasonably well.
Grigri
The Grigri functions much the same as the plaquette style belay device, with pretty much the same pros and cons. You may well have one with you when rock climbing, but not for a crevasse rescue situation. A Grigri also has the benefit of being able to release under load, which can be a great help if you need to release tension for some reason.
As mentioned just above with the ATC Guide, I did some testing on the Grigri to check the real world efficiency. It turns out to be the same as the ATC guide, which is pretty much the same as just running the rope to the carabiner. In other words, it does not introduce any significant extra friction. I tested agree with a 10 pound weight and a 100 pound weight; the results were the same in both cases.
The real world mechanical advantage with the Grigri as a progress capture is about 1.5 to 1. This is a good thing! It means you can use commonly carried devices as a progress capture with no friction penalty of decreased efficiency.
Petzl Traxion
These little suckers have a high efficiency pulley combined with an ascender type spring loaded rope grab. They give you a great easy pull combine with zero loss of progress . Pros: work perfect. Cons: cost about $100, ouch! (Kind of a lot for seldom-used rescue gear, IMHO . . .) Traxions come in various flavors: the Micro, the Mini (the one I have, in the photo below, now discontinued) and the Pro. For alpine climbing, you want the Micro.
If you’re doing a 1:1 haul of fairly heavy bags on a big wall climb, you probably want a slightly larger diameter pulley wheel to get a small increase in efficiency. One popular ratchet pulley for big wall climbers is called the Kong Block Roll. (I don’t have one, but word is they work great.)
MA in the real world
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.
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.
Progress capture - efficiencies of various devices
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.
So, we have more than few options for Progress capture / ratchet devices. But which one’s best, in terms of minimizing evil friction in our MA systems?
I did a few studies on the efficiency of different pulley, carabiner and ratchet systems, and found some to be dramatically better than others.
It's important to note that the efficiency of the ratchet varies a lot on your rigging. If it's a progress capture for a 1:1, the efficiency might be terrible. But, if it's a progress capture for a 3:1, the efficiency can be much better.
Here’s how I set up my 1:1 study.
All 1:1 pull with a redirect through the anchor, no mechanical advantage
Fixed anchor point around head level, could be pretty much anything
About a 9 mm dynamic rope
10 pound barbell plate
Various types of pulleys / ratchets clipped to anchor point
Inexpensive spring scale from Amazon, about $11, cloved to the pull rope, LInk: https://www.amazon.com/gp/product/B00ZWNGZFO/
The set up looks something like this. The scale is cloved hitched to the left side “pull rope”.
I set up the pulley or ratchet, then slowly pulled the spring scale to raise the weight and noted the scale reading during the steadiest pull I could manage. The measured force is approximate as I used a cheap spring scale, but I think it’s accurate enough to give a rough idea of efficiencies.
I tested pretty much every flavor of pulley or ratchet mechanism that I owned.
All of the pulling force listed below is for a 1:1 redirected pull of a 10 pound weight.
Here’s a summary of the raw data.
and here’s a bar chart:
Here are some takeaways.
Never use a garda hitch or ATC in guide mode as the ratchet in a 1:1. Friction is HUGE, it took about 60 lbs of pull to move a 10 lb weight! (If this is your only option as a progress capture, you’re probably better off setting up a separate 2:1 on the load to lift it, and then when the rope has some slack, use the hitch or ATC to capture the progress of the loose rope.)
Pulling force of round stock vs “I-beam” carabiners is pretty similar, not really noticeable in the real world.
DMM Revolver carabiners did not seem to reduce friction very much, comparable to a plain round stock carabiner in this study. (They were actually worse.)
2 identical carabiners side by side did not change the friction much compared to a single carabiner.
If a prusik if jamming in your pulley even a little (as I had), it adds noticeable friction.
Using a 5.5 mm Spectra cordelette gave better efficiency than a 9 mm diameter climbing rope. This gave the best efficiency of 87%.
Pulley ratings from manufacturers are probably calculated under ideal lab conditions, and not under real world testing conditions like I tried to model.
As I covered in this article, “Progress capture options”, things are quite a bit different with a 3:1. Surprisingly, using an ATC guide or similar device, or a Grigri as a progress capture introduces no significant amount of friction into the system, at least according to my limited testing.
I tested this with both a 10 pound load and a 100 pound load. The efficiencies were just about the same with each one. A 3:1 Z drag set up with just carabiners at the change of direction gets a real world mechanical vantage of about 1.5 to 1.
Check out the photo below. You would think that ATC Guide would had a ridiculous amount of friction, right? In fact, it doesn't really add any at all.
Finally, we have this interesting chart created by Yann Camus of BlissClimbing. (Shared here with permission from Yann. He’s an expert in rope soloing, and if you want to learn this from someone who's been there done that, Yann would be an excellent choice.)
It shows a few interesting general concepts: The smaller diameter cord, the greater the efficiency. The largest diameter pulley, 3 inches, gave the highest efficiency. The DMM revolver carabiner was slightly better than a regular carabiner, but not nearly as good as a proper pulley. (If you're squinting at this graph on a phone, it's easier to see on a desktop / larger screen.)
image: https://blissclimbing.com/en/
Does an MA system make hauling easier?
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.
This might sound like a trick question. The first response might be, “Duh, of course it makes it easier, you can pull more load with less effort!”
Well, that's true, MA does multiply your pulling effort. But this increased lifting force comes at a cost of increased lifting distance. As the economists say, “There’s no such thing as a free lunch!”
Example: Imagine you’re on a big wall climb with a 200 pound haul bag, and your climbing partner is a big burly rugby player who weighs 250 pounds. RubgyDude leads the first pitch, which is 100 feet and happens to be a little overhanging. (This is great for hauling, because it means no friction between the haulbag and the rock.) RugbyDude decides to rig a 1:1, because he knows he outweighs the haul bags and just wants to get the pain over with. Besides, it's only the first pitch and he’s still feeling pretty fresh.
The next pitch is yours. It also is 100 feet long and overhanging. You finish your lead and start thinking about your hauling set up. At this point, you have to ask yourself two questions: 1) Do I weigh less than the haul bags? and 2) How much pain do I want to suffer? If you weigh under 200 pounds, then obviously a 1:1 with just your bodyweight is not going to move the haul bags, and you’re going to have to use some kind of MA to get that bag up the cliff. If you happen to weigh a bit over 200 pounds, it might technically be possible to do a 1:1 haul, but you know you're going to be a wreck when it's over. You decide to rig a 2:1 haul.
When the bag reaches the anchor, you have moved the same amount of weight over the same distance as RugbyDude did on his pitch, you just pulled in 200 feet of rope to his 100 feet. In the end, the same amount of “work” was done, even though the 1:1 would've hammered you, and the 2:1 allows you to still feel pretty good when you have finished. HINT - This is why the 2:1 hauling system is popular on big walls when you have a serious load.
There’s not a correct answer here; it has to do with your own strength, bodyweight, and willingness to suffer.
Think of it this way. Would you rather lift 200 pounds once, or 100 pounds twice?
Or, as Sticky discovered above when she set up the 2:1, “Do you want to work hard or do you want to work smart?” Talk to RugbyDude in a couple of days and see how chipper he's feeling at the top of pitch 15; he might think that 2:1 haul is sounding pretty good!
Does an MA system put more load on the anchor?
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.
Warning to non-enginerds: this question gets a little technical, feel free to skip it if you want. The takeaway is YES, it usually does, so make your anchor extra stout. If you want to know why, read on.
Ahh yes, this is a very interesting question, and one subject to much debate on the inter-webs.
Lots of folks think that an MA system always magnifies the load on the anchor. For example, if you have a 2:1 system lifting a 100 kg load, then the anchor is holding 200 kg. A 3:1 system, the anchor is holding 300 kg, etc.
This is NOT correct!
Theoretically, an MA system does not put more force on the anchor.
In the real world, with friction, you can magnify forces on the anchor.
Let's first have a look some ground rules, and then we’ll get into the friction part.
The higher the MA of the system, the more force goes to the anchor.
Let's have a look at the diagram below, made with the clever software vRigger. Assuming no friction in the system, and a load of 100 kg, there's quite a large difference in the load that gets transmitted to the anchor with the 2 to 1 compared to the 3 to 1. This is a pretty straightforward rule that applies to all MA systems.
Why is this? The lower the MA of the system, the more of the load you’re supporting with your hand, and the less goes to the anchor. With a 2:1 system, about half the load is on your hand and half is on the anchor. With a three to one system, roughly 1/3 of the load is on your hand and the other 2/3 of the load is on the anchor.
made with vrigger software
A redirect on the anchor for pulling increases the force on the anchor.
This is a great rule to keep in mind when you want to reduce forces on your anchor, such as crevasse rescue with one buried dead man.
Check out the example below with a 2:1. With the standard set up on the left, about 0.5 times the load goes to the anchor. But when you redirect as shown on the right, about 1.5 times the force of the load goes onto the anchor.
made with vrigger software
In the real world, friction can magnifies force on the anchor.
Let's revisit Sticky, who is pulling a simple 1:1 pull, redirected through the pulley high up in the tree. Only this time, instead of the tree branch conveniently hanging out over the edge of the cliff, the tree is set back, so the rope is running over a rock ledge. For this discussion, let's say that Sticky needs to pull with an extra 50 pounds of effort to overcome the friction of the rope running over the ledge. For her to lift the 100 pound load, she needs to generate 150 pounds of effort.
If she pulls with 150 pounds of effort to raise the load, that means there is now 150 pounds on the strand coming out the other side of the pulley. Which means the anchor is holding 300 pounds rather than 200 pounds. Remember, when you redirect your pull, that redirect point will receive twice the force that you apply.
Note that this does not have anything to do with the actual mechanical advantage of the system. Instead, it's an example of how friction in your hauling system can result in increased forces on your anchor, regardless of the mechanical advantage you’re using.
Is this a problem? Maybe, maybe not. Do you have an anchor on a stout tree limb or three well equalized points of rock protection? Probably not.
Or, is your anchor a a vertical snow picket, and you're about to set up a 3 to 1 haul with two strong people trying to pull somebody out of a crevasse? Then, that lone anchor might be a significant problem. Take a few more minutes and make a deadman anchor from that picket, or better yet, two that share the load.
With this in mind, let's consider a real world crevasse rescue scenario.
One person from your 3 person rope team fell into a crevasse. The rope going to them is cut deeply into the crevasse lip, adding a lot of friction.
You only have 50% efficient carabiners instead of 90% efficient pulleys.
On your alpine climb, you’re using small diameter, stretchy dynamic ropes.
You set up at 3:1 Z drag, and you and your partner both start pulling with your entire body weight. To move the load, your pulling force has to overcome all the extra friction from the carabiners, the rope against the snow, (and the inefficiency of the stretchy rope) and that pulling force has to be transmitted to the anchor. How much force? Hard to exactly say, but two people pulling as hard as they can on a Z drag with a lot of real world friction can generate a BUNCH! That extra force has to be absorbed by something - most of it’s going onto the anchor. (Better bury another picket as a deadman!)
You may be thinking: “Here I am with my buddy, and we’re both pulling as hard as we can on this 3:1 Z drag, trying to lift our 150 pound partner out of the crevasse. Me and my partner weigh a combined 300 pounds, so in theory, if we’re pulling with a 3 to 1 we should be creating 900 pounds of pulling force, but we’re still only barely lifting my 150 pound friend. This is way harder than it should be . . .”
Here's another way to handle that crevasse rescue scenario.
Your three person team is carrying high-efficiency pulleys, a Micro Traxion or two, and enough extra rope with each and person to be able to drop a loop down to the person in the hole.
After your buddy falls in, can you drop a loop of rope to them which they clipped to the harness with a Traxion. You also prepare the lip on top, knocking down some loose snow and putting an ice ax underneath the dropped loop to help reduce friction.
The victim, who is functional, can greatly help in this process by pulling down on one of the draft strands. This effectively reduces his weight and friction on the other strand that’s being pulled.
Now, the two partners on top can easily pull up the victim, and have a minimum load on the anchor.
To use a more extreme example, let’s say you get your car stuck in a ditch, and you rig a 9:1 with a big tree as anchor to try to pull it out. Now you have basically a tug of war between the tree and your car. When you pull onto 9:1, the anchor (in theory) gets your pulling force multiplied by 8.
Now, say someone else steps up to help you pull. How much force on the anchor components can two strong people apply? That’s now the force of two people pulling multiplied by eight. Now you’re probably getting pretty close to the safe working limits of some of your equipment. There’s a chance the weakest links on the system could start to fail, like prusiks sliding or breaking or even hardware failing. Hopefully the car moves before anything breaks or slips, but the point is, your anchor and the components of your pulley system need to be stout enough to handle these magnified forces.
So, here is the final answer - In the real world, mechanical advantage systems often result in extra force on the anchor, because of the extra effort needed to overcome friction. The greater the MA of your system, and the heavier the load you’re trying to lift, and the more friction is involved, the stronger your anchor needs to be.
This is discussed in the excellent book “The Mountain Guide Manual”, by Marc Chauvin and Rob Coppolillo, pg 276.
The 3 kinds of pulley systems
Getting into slightly more advanced MA topics - the differences between simple, compound and complex pulley systems.
I'm reading up on pulley systems, and I’m hearing about “simple”, “compound”, and “complex”. What do these terms mean, and which one should I use?
Now, this is heading into slightly more advanced territory, but if you’ve read this far you hopefully still have an interest in slightly esoteric things like this. :-) As to which one to use, there’s not a quick and easy answer.
The one potential issue with the compound and complex systems is that you usually have to reset the pulleys more often as they “collapse” (or, are pulled into each other) when you pull. If you have a large working area, like the top of a crevasse, this is probably not a big deal. If you have a tiny working area, such as a hanging rock belay, then it might be more of a problem.
If you want to geek out on this, look at the YouTube video links at the bottom of the page on compound pulleys and start playing around on your living room floor. That's really the single best way to learn this. You can do it with some parachute cord and a few carabiners, you don't need pulleys or a even a real climbing rope.
1 - Simple system
When you pull the rope, the pulley(s) move in the same direction and the same speed toward the anchor.
As the rope is pulled, the pulley moves toward the anchor at a constant speed. There are three strands of rope going to and from the load and load strand, so this means it's a 3:1 MA. This is also known as a “Z drag”, because the shape of the rope is a “Z”. (If you tilt your head to the left . . .)
In a simple pulley system, when the rope end terminates and is attached at the anchor, then the MA will result in an even number (e.g. 2:1, 4:1, 6:1, etc.).
When the rope end terminates and is attached at the load, then the resulting MA will be an odd number (e.g. 3:1, 5:1, etc.).
In the photo below, the rope end attaches to the load, so we have an odd MA number, 3:1.
A 3:1 simple system. The pulley moves at a constant speed toward the anchor.
2 - Compound system
When you pull the rope, the pulleys move in the same direction, but at different speeds toward the anchor.
This can be created by building a 3:1 Z drag, and then adding a 2:1 onto the strand you’re pulling. With a compound system, the mechanical advantage of each separate pulling system is multiplied.
Below, we see a 3:1 on the white rope, and a 2:1 on the black rope. Together, the two systems are multiplied to get a 6:1. Note that the white rope will move the load 1 foot for every 3 feet of rope you pull, while the black rope moves upwards 1 foot for every 2 feet of rope you pull. Therefore, the black rope will reach the anchor point before the white rope, meaning you need to reset the system more often.
Note - If you have 3:1 set up and and need more pull, making a compound 6:1, as we see below, is often a great idea. An example would be crevasse rescue on a two person team, when one person on top may have to do all the pulling. If you have a lot of friction from the rope running through the snow, and/or your partner in the crevasse is not able to assist you, the 3:1 is probably not going to work. Then, the 6:1 is going to be your best friend. Adding the 2:1 only requires one additional pulley and carabiner. Sweet!
Note: For a compound pulley system, you can add the very Crafty Rope Trick (CRT) of building a second anchor that’s farther away. This can allow you to completely collapse the 3 to 1 system before the 2 to 1 system collapses, which means you need to reset the system less often. Granted, this trick is probably more appropriate for professional riggers or maybe search and rescue teams, and not so much for climbers, but it’s still a pretty cool trick.
6:1 compound system, 2:1 on a 3:1.
Two different pulleys move at two different speeds in the same direction.
3 - Complex system
A complex pulley system is one that doesn't quite meet the definition of a simple or compound. A complex system has a pulley(s) that moves in the opposite direction of the load. Complex MA systems are okay, but a simple or compound system is usually a better choice, because they are generally easier to rig and require fewer resets.
Below we have a 3:1 simple system. With the addition of a friction knot (red) and carabiner, we now have a 2:1 pulling on the 3:1. Because this is a complex system, the two components are added together, giving a 5:1.
This is now a complex 5:1 system. When the rope is pulled, both pulleys move toward one another. When the pulleys touch (aka “collapse”), you need to reset the system. Probably not a problem if you have a large area to work in. But if you’re on a tiny rock ledge, you’ll only get a foot or so of lifting until the pulleys collapse, which is going to be a hassle.
Compare this with the compound 6:1 diagram just above. With the 6:1, you get a little more MA, plus avoiding the collapsing pulley problem, so that's why the complex system is usually not the top choice.
5:1 complex system.
A basic 3:1 with a red friction knot added, and the pull strand redirected through it.
Two different pulleys move toward each other at different speeds.
What's the MA of my system?
Here’s how to calculate the actual MA of a given pulley system.
I get confused when I look at these fancy diagrams with ropes running in all different directions. How can I figure out what the real mechanical advantage is of a given system?
You're right, things can be difficult to figure out! At one level, you could say it doesn't really matter. If the 3:1 isn't working, you can add or multiply a 2:1 on top of this, and hopefully the resulting 5:1 or 6:1 gets the job done. The number doesn't really matter in the end.
But, since you asked the question . . . Remember our discussion simple, compound, and complex systems from this post? (Go read it now if you have not seen it.)
The answer of “what’s my MA” varies depending on which one of these systems you’re using.
For a simple system, we calculate the MA by counting how many strands of rope are going to and from the movable pulley(s) on the load or load strands. And, always remember, any pulley or carabiner that’s fixed on the anchor only changes the direction of pull, and does not create mechanical advantage. Let's look at a few examples.
Also, in a simple pulley system:
When the rope end terminates and is attached at the anchor, then the MA will result in an even number (e.g. 2:1, 4:1, 6:1, etc.).
When the rope end terminates and is attached at the load, then the resulting MA will be an odd number (e.g. 3:1, 5:1, etc.).
There’s 1 strand of rope coming from the load. So, 1:1 simple system (no mechanical advantage gained).
There’s 2 strands of rope going to and from the load. So, 2:1 simple system. (Rope end attached to anchor, even number MA of 2.)
There’s 3 strands of rope going to and from the loaded strand. So, 3:1 simple system. (Rope end attached to load, odd number MA of 3.)
For a COMPOUND pulley system, the hauling systems are MULTIPLIED together.
For example, this is a 2:1 on top of a 3:1, so multiplied we get a 6:1.
image: https://roperescuetraining.com/raising_6-to-1.php
For a COMPLEX pulley system, the hauling systems are ADDED together.
For example, the image on the right shows complex system. The 2:1 on top of a 3:1 added together gives a 5:1.
image: https://roperescuetraining.com/raising_5-to-1.php
For more on simple, compound and complex pulley systems, see post “The 3 kinds of pulley systems”.
There‘s also a more math oriented way to calculate your MA. It’s called the “T-method, aka “counting tensions”.
Here are two excellent videos on using the T method to not only calculate the theoretical mechanical advantage but to also account for friction in your system. If you want a deeper understanding of this, this is a great place to start.
Pulley size and rope stretch
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.
What effect does pulley diameter have on efficiency?
A larger diameter pulley wheel (aka sheave) is technically more efficient than a smaller diameter pulley. But it’s a trade off: a larger pulley has increased bulk, weight and cost. For example, in a 1:1 haul, you gain about 7% efficiency going from a 1.5” pulley to a 3.75” pulley. This efficiency increases with really big loads (600 lbs+) and larger mechanical advantage, such as 6:1 and 9:1. So, it's probably of interest to mountain rescue teams, of moderate interest to big wall climbers, and not very relevant to alpine climbers. As long as you use a good quality pulley, the diameter doesn't matter much in climbing applications.
In the real world, on, say, a crevasse rescue, you're probably not going to notice the difference between a pulley that's 80% efficient versus a pulley that's 90% efficient. Get a small-ish rescue pulley from a name brand company and don’t stress about the actual efficiency rating.\
A trusted “workhorse” pulley is the Petzl Rescue - rated to 95% efficient with a 1.5 inch / 38mm metal sheave.
In the chart below, note the low carabiner efficiency - about 53%, ouch!
Is it better to use static rope or dynamic rope in a hauling system?
Steel cable has essentially zero stretch, and offers the highest efficiency. Next best is static rope. Third-best is dynamic rope. Alpine climbers may only have a dynamic rope available, so they may not have a choice. (However, this is one more argument in favor of using a static rope for glacier travel, see this tip for more on that.) Big wall climbers, however have a choice between a static or dynamic haul rope. Static haul ropes are more popular on big walls, and this is one of the reasons, greater hauling efficiency.
When you haul a big load with a dynamic rope, you have to pull all the “stretch” out of the rope before the load even starts to budge. As you might imagine, this is not much fun. Once all the “stretch” has been removed from the rope, if you then pull in a steady constant speed, all ropes are going to behave pretty much the same way. However, in the real world, you're going to have a pull that isn’t so smooth; you're going to accelerate and decelerate. When you do this, the dynamic rope is stretching and relaxing, back-and-forth, and this absorbs energy and lowers your efficiency.
See the graph below. Steel cable, with a large diameter pulley, is about as good as it gets, 98% efficiency. The other four flavors of static rope are all pretty darn close. Note again, the efficiency increases slightly when you go to a larger diameter pulley wheel. Too bad they didn’t test dynamic rope in this experiment, but it was done by a mountain rescue team, and they almost always use static ropes for hauling systems.
image: http://itrsonline.org/wordpress/wp-content/uploads/2014/09/McKently2011_ITRSPresentation.pdf
6:1 compound pulleys in the real world
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.
Say you’ve built a 2:1 mechanical advantage (MA) system or 3:1 MA system, and it's not quite doing the job. You need some greater pulling force, so how do you do it? Here are two approaches that combine a 2:1 and a 3:1 to make a 6:1 MA system. If you find yourself in a one person rescue situation, a rig like this might be required.
Both of these examples are known as a compound pulley system. With a compound system, you have one simple system pulling on another simple system. The pulleys move in the same direction, but at different speeds, than the load.
In a compound system, the hauling systems are multiplied to get the final mechanical advantage. In both of these examples we have a 3:1 multiplied by a 2:1, so the resulting theoretical mechanical advantage is 6:1.
With a 6:1, you need to pull 6 feet/meters of rope in order to move the load 1 foot/meter.
Enough with the terminology and theory, let's see how to build these for real. If you want, go get your gear, lay it out on the floor and follow along. (Please don't pull heavy furniture around in your house, it's rough on the floor. =^)
Let’s start with a 3:1 system, then add a 2:1 on top of this to get a 6:1.
This is one of many different ways you can set this up, with various combinations of hardware, pulleys, rope grabs, etc. This has a Petzl Mini Traxion progress capture pulley at the anchor. You could use a regular pulley and prusik loop here as well.
Let's start with a basic 3:1 Z drag.
Step 1 - Clip some cord onto the anchor master point. Here it’s an untied cordelette. It could also be the far end of the rescue rope itself.
Step 2 - Tie a prusik in the hauling strand as shown and clip a carabiner and pulley (if you have one) to it. (If you don't have a second prusik loop, you could tie a clove hitch in the white rope. You would have to retie at every time you reset the system, but it works.)
Step 3 - Clip the cord into the pulley and pull.
That's it, a 2:1 on top of a 3:1, resulting in a 6:1 theoretical mechanical advantage.
Here’s a similar setup, but reversed. We're going to start with the 2:1 and add a 3:1 on top of it, resulting in a theoretical 6:1.
Again, this is one of many different ways you can set this up, with various combinations of hardware, pulleys, rope grabs, etc.
Let's start with the basic 2:1. Note that in this 2:1, the red Traxion progress capture pulley is on the load, rather than the anchor. This can be advantageous in certain rescue situations.
Step 1 - Clip a carabiner into the anchor master point, and clip the pulling rope to this carabiner. (This changes the direction of pull and does not add any mechanical advantage.)
Step 2 - Add a prusik to the pulling strand near the load.
Step 3 - Clip a carabiner (and a pulley if you have it) to the prusik.
Step 4 - Clip the haul rope to the pulley, and pull.
You’ve added a 3:1 on top of a 2:1, giving you a theoretical 6:1 system.
If you happen to have another pulley, add it to the redirect carabiner that's on the anchor. If you have only one pulley, it’s in the correct place; on the prusik that's closest to your pulling hand.
Finally, here is a great video by IFMGA Certified Guide Jeff Ward showing the 6:1 “Z on a C” System applied to crevasse rescue. (His rigging is slightly different than what I shared above and that he has the progress capture above with him and not down on the climber, but other than that the system is identical.)
Show me the 9:1
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!
OK, I’m on a SAR team and need to know fancy systems, or I’m a river guide who might need to pull a wrapped raft off a midstream boulder, or I like to drive offroad and need to know how to pull my truck out of the ditch. I'm ready for the 9:1! How do I do it?
Well, if you’ve read this far, you're ready for the fancy stuff. A 9:1 is a compound system, with a 3:1 stacked on top of another 3:1. Remember, with a compound system, the forces of each section are multiplied together to get the final MA, so a 3:1 on a 3:1 gives you a 9:1.
Important: if you have a high mechanical advantage system, say 6:1 or 9:1, and you are REALLY pulling on it (several strong people) to move a serious load (stump, car in the ditch) you may be getting dangerously close to the safe working limit of some of your equipment, such as a pulley or carabiner.
If you’re in this situation and feel you need to apply more pulling force, it’s probably a good choice, provided you have the equipment, to set up a completely separate system, may be on a new anchor, and pull simultaneously on both systems.
Granted, recreational climbers should pretty much never find themselves in this situation, but if you’re pulling out a stump or your truck, keep this in mind.
Many people (like me!) find looking at a diagram of a 9:1 makes their head spin. But as we like to stay around here, it's a better show than a tell. When you see it demonstrated properly it's actually pretty simple. Here is a nice video that shows you how to do it.
And, if you're the diagram type, here’s a pretty slick example of a 9:1.
image: https://roperescuetraining.com/raising_5-to-1.php
What's the mechanical advantage? It's relative!
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.)
The illustrations in this article, used with permission, come from the excellent website RopeLab, run by Australian rigging expert Richard Delaney. RopeLab has a ton of great material for anyone who wants to dive into ropes, rigging, and mechanical advantage, check it out! There's a fair amount of quality free information, but getting an annual subscription unlocks the entire website. You can also connect with Richard on Instagram and his YouTube channel, where he has loads of concise, informative videos.
These diagrams come from a Ropelab online mechanical advantage quiz, which you can find here.
Okay, clever rope wizards and mechanical advantage fans. Here are some questions and diagrams that might leave you scratching your noggin.
A standard principle in mechanical advantage systems is that any change of direction that's on the anchor only serves as a redirect, and does not add mechanical advantage. Well . . . that's true most of the time, but not when the “load is also doing the lifting.”
The mechanical advantage of the system depends not just on the rigging. It depends on who is doing the pulling - a person who’s “in the system” or a person who’s out of it. Let's look at a few examples.
1 - This image shows someone standing on the ground attempting to raise their partner. What’s the Ideal Mechanical Advantage of this system (ignoring friction)?
image: https://www.ropelab.com.au/ropelab-quiz-1-mechanical-advantage/
Answer: It's a 1:1 mechanical advantage. The person on the ground is pulling the weight of the person hanging from the rope 1:1 through a redirect. No mechanical advantage is gained. The person on the ground needs to pull 1 meter of rope to lift their partner 1 meter, so it's a 1:1.
2 - This image shows a person attempting to raise themself by pulling down on the rope. What’s the Ideal Mechanical Advantage of this system (ignoring friction)?
image: https://www.ropelab.com.au/ropelab-quiz-1-mechanical-advantage/
Answer: Exact same rigging as before, but this time the person hanging from the rope is doing the lifting. This time, the mechanical advantage is 2:1! For the climber to go up 1 meter, they need to pull 2 meters of rope through their hand, so the mechanical advantage is 2:1.
Richard Delaney, from the YouTube video link at the bottom of this page: “Mechanical advantage is technically the ratio of the applied force to the input force.” There are two strands of rope holding the climber’s weight. If the climber weighs 100, that means each strand is holding 50. If the climber pulls down on the rope with a force slightly more than 50, they will start to move up. This means the applied force is 100, and the input force is 50, so therefore we have a 2:1.
Does this leave you scratching your head? It did for me when I first saw it! Next time you see a sport climber after a fall, pulling down on the belay rope to lift themselves back up to their high point, this is how they’re doing it, with a 2:1.
3 - Let's take this idea a step further. This image shows someone attempting to raise their partner by pulling down on the rope. What’s the Ideal Mechanical Advantage (ignoring friction) of this system?
image: https://www.ropelab.com.au/ropelab-quiz-1-mechanical-advantage/
Answer: 2:1, with a redirect through a second anchor point. There are two rope strands supporting the climber’s weight, so it's a 2:1.
4 - This image shows a person attempting to raise themself by pulling down on the yellow rope. What’s the Ideal Mechanical Advantage (ignoring friction) of this system?
image: https://www.ropelab.com.au/ropelab-quiz-1-mechanical-advantage/
Answer: 3:1. Just as in example #2, if the person pulling on the rope is the same as the load, the mechanical advantage increases, even though the rigging is exactly the same. In this case, there are three rope strands supporting the climber’s weight. For the climber to move up 1 meter, 3 meters of rope needs to be pulled, so the mechanical advantage is 3:1.
Back to Richard’s explanation of the ratio of input force to applied force: We have THREE strands of rope holding the climber’s weight. If the climber weighs 100, that means each strand is holding 33. If the climber pulls down on the rope with a force slightly more than 33, they will start to move up. This means the applied force is 100, and the input force is 34, so therefore we have a 3:1.
Isn't that interesting? The mechanical advantage of the system depends not just on the rigging, but on where the pulling force is coming from.
Here’s a climbing application of this principle.
Below is a screen grab from a video featuring IFMGA Guide Jeff Ward ascending out of a crevasse. He's using this 3:1 mechanical advantage system to help him climb the rope. I have an entire article on this clever ascending system, read it here.
Here's the set up. This works way better than the traditional “go up the rope with two prusiks” method.
Here's another way to think about it, in a horizontal plane.
You're out 4x4 wheeling in your truck, and you get stuck. You take the winch cable from the front of your truck, put it around a tree anchor, and then bring it back and connect it to your truck. You turn on the winch and slowly pull yourself out. What is the mechanical advantage?
If you clip the end of the winch cable to the tree, you would have a 1:1. But if you attach it back to the truck, you create a 2:1, because the load (truck) is also doing the pulling.
image: https://www.ropelab.com.au/ropelab-quiz-1-mechanical-advantage/