Mechanical advantage for climbers

Here's a series of blog posts that cover mechanical advantage systems for climbing.
(Disclaimer, it's my blog, it's non-commercial and has no advertising.)

If you're already an engineer or have been at the game for a long time, you will probably know most of this.
But for newer climbers or non-engineers, you'll probably find it helpful.
It's written in simple terms for the non-engineer, uses no math formulas, and has real world test results to back up the theory.

It answers some fairly common questions such as:

• If I'm trying to build a 3:1 and only have one carabiner, where should I put it?
• Do I really need to carry a rescue type pulley, or can I get away with using a carabiner?
• Can I replace a pulley with a DMM Revolver carabiner?
• If I use various pulleys and carabiners in different combinations, what are the real life forces needed to move a load?

Check it out and let me know what you think.
https://www.alpinesavvy.com/mechanical-advantage-for-climbers

Damn, John! So far, these are nice! 

Jesus, dude! You really put some work into these.

Great effort John,
you might like to read my web page http://people.bath.ac.uk/dac33/high/13SelfRescueSenarios2.htm#ahaulingsystemthat

I spent a lot of time at a local crag seeing if I could haul someone with normal climbing kit (no pulleys) using any of the systems in any of the textbooks on self rescue. I couldn't under many situations.

The 2:1 Chongo was by far the best, and if the person can't help sometimes the only option

These are awesome, thanks!

Nice blog, definitely gonna keep me busy for the next couple hours while I'm at work lol

Good work!

Two comments based on an initial fast perusal.  

(1) The efficiency observed for 3:1 haul with two round-stock carabiners is the same result one gets from a calculation assuming a loss of 1/3 of the load to friction over each carabiner.  In other words, the experimental evidence is exactly what the theory predicts.  Edit: this is wrong---see my post below.

(2) The slightly lower efficiency of the DMM revolver vs. an ordinary round-stock carabiner is puzzling.  Any explanations for this result?

rgold wrote:(2) The slightly lower efficiency of the DMM revolver vs. an ordinary round-stock carabiner is puzzling.  Any explanations for this result?

My experience (at least with my ropes) with the revolver is that under load the rope rides up out of the wheel due to (I presume) the geometry of the biner.   I’m pretty sure Jim Titt mentioned something similar in a different thread.

On the topic of pulley efficiency, does anyone know how good the Petzl Ultralegeres are?  I tried looking on Petzl's website, but they did not list that.  Are they worth the $6 as an emergency pulley?

David Coley wrote: Great effort John,
you might like to read my web page http://people.bath.ac.uk/dac33/high/13SelfRescueSenarios2.htm#ahaulingsystemthat

I spent a lot of time at a local crag seeing if I could haul someone with normal climbing kit (no pulleys) using any of the systems in any of the textbooks on self rescue. I couldn't under many situations.

The 2:1 Chongo was by far the best, and if the person can't help sometimes the only option

First, my previous post had an errror, based on faulty memory.  If each carabiner loses 1/3 of the load to friction, the 3:1 system has a 2.1:1 MA, which is better than the observed value of 1.6:1.  In order to get 1.6:1, the load over each carabiner has to be reduced by about 58%, not the 33% used for the 2.1:1 result.  This suggests that in the hauling configuration, carabiners are less efficient than commonly assumed.

Based not on "a lot of time at a local crag," but rather just occasional practice days, I arrived at the same conclusion as David with his more careful analysis.  There is no way you can count on being able to raise an incapacitated climber more than a few feet with just slings and carabiners.  In the right low-friction scenario maybe, but at the same time in a just as if not more likely high-friction scenario you won't be able to budge them.

The situation is worsened if the technique of using a plate in guide mode as a progress capture device is employed, because this introduces far more friction than a carabiner.

3:1 works for cravasse rescue (although now many people carry a minitrax and sometimes a second pulley as well), because the rescuer has a lot of terrain to work with.  But on a small ledge, with the rope running over various rock edges (and if the injured person is a second, the rope also running through protection carabiners) I'd say the chances of carrying out a long upward haul are poor. 

I wonder what tests would reveal for this theoretically 3:1 system, that allows for a downward pull.  In theory, assuming the 1/3 carabiner friction reduction, it comes out worse than the standard 3:1 (at 1.8:1 as opposed to 2.1:1).

You are correct, the Ontario pulley setup is less efficient than the traditional 3:1 pulley system.

However, it still might be "better" because the rescuer should be able to apply more force in a downward pull (the Ontario system) than by pulling upward in the traditional 3:1 system.

I too would be interested in some real world testing results/data.

If you have the $$ and want a pulley that will be REALLY useful in a rescue situation I would recommend picking up a petzl micro traxion.  It combines a sealed ball-bearing pulley (91% efficiency) with a toothed progress capture ratchet, all in a very small and light (85g) package.  Just about every system described here could be made much more elegant and effective with one of these little beauties.

With two of them you could hoist a sumo wrestler!

mbk wrote:

My experience (at least with my ropes) with the revolver is that under load the rope rides up out of the wheel due to (I presume) the geometry of the biner.   I’m pretty sure Jim Titt mentioned something similar in a different thread.

That's about ir, the shape of the biner was optimised for use as a runner, wrap the rope 180 and more load and there's no real benefit. The friction is about the same as a 12mm biner.

rgold wrote: Good work!

Two comments based on an initial fast perusal.  

(1) The efficiency observed for 3:1 haul with two round-stock carabiners is the same result one gets from a calculation assuming a loss of 1/3 of the load to friction over each carabiner.  In other words, the experimental evidence is exactly what the theory predicts.  Edit: this is wrong---see my post below.

(2) The slightly lower efficiency of the DMM revolver vs. an ordinary round-stock carabiner is puzzling.  Any explanations for this result?

rgold,

I was curious about the DMM revolver results myself. I was expecting greater efficiency, but that's not what I found at least with that particular diameter of rope that I was using, I think about 9 mm.
Perhaps with a brand new carabiner, with the root of a particular kind of sheath, and if the pole is exactly in line with the revolver, then it might work better.
My guess is that if the direction of pull starts to go to one side or the other, it starts to negate the pulley working correctly.

All you need to do to do this little observational study yourself is to buy a cheap digital spring scale, about $11 on Amazon.
Give it a go yourself, it's a good way to spend a rainy afternoon.

I just made a separate post on this in general climbing, have a look there.
https://www.mountainproject.com/forum/topic/116586082/dmm-revolver-carabiners-dont-work-very-well-as-pulleys

john

nice summary!

Brady3 wrote: On the topic of pulley efficiency, does anyone know how good the Petzl Ultralegeres are?  I tried looking on Petzl's website, but they did not list that.  Are they worth the $6 as an emergency pulley?

Brady - I think the short answer is no. At least, I have not had good luck with them in crevasse rescue type situations. I address it briefly on this blog post:

https://www.alpinesavvy.com/blog/a-few-basic-questions-and-answers-about-ma-systems

rgold wrote: The situation is worsened if the technique of using a plate in guide mode as a progress capture device is employed, because this introduces far more friction than a carabiner.

I am in complete agreement with this. This was one of the more shocking things that I found with my little redirect experiment - it took about 65 pounds of pole to lift a 10 pound barbell weight when it was redirected through an ATC guide in auto block mode! That is an awful efficiency of somewhere around 15%! So the take away here is you never want to Use an ATC guide as a progress capture device, if you're putting any weight onto it at all. (Now, if you did the lifting with some sort of 2:1 piggyback system, and then used the ATC Guide to capture the progress with the slack rope, that's a different story.)

https://www.alpinesavvy.com/blog/progress-capture-efficiencies-of-various-devices

Sam Skovgaard wrote: If you have the $$ and want a pulley that will be REALLY useful in a rescue situation I would recommend picking up a petzl micro traxion.  It combines a sealed ball-bearing pulley (91% efficiency) with a toothed progress capture ratchet, all in a very small and light (85g) package.  Just about every system described here could be made much more elegant and effective with one of these little beauties.

With two of them you could hoist a sumo wrestler!

Hey Sam,

Right you are, Micro traxion is a beautiful little piece of gear. However, at about $100, it's a somewhat optional piece of kit for many climbers. Elegant and effective comes at a price, unfortunately. :-)

Also, I think you need to take that 91% efficiency rating with a grain of salt, as it probably comes from the Petzl marketing department and not from the engineering department. As you can see at the link below, I did a test with the Petzl Mini Traxion, which is the one I have which is now discontinued. I don't know what the exact efficiency rating on that is, but it's pretty close to the Micro, but not quite as good.

My test showed it took about 13 pounds of pull to left a 10 pound barbell plate, which translates to about 77% efficient. I have a feeling in the testing lab, Petzl is probably using small diameter steel cable to come up with that 91% value, which of course does not apply to us using dynamic ropes in the real world.

Hey, go buy an $11 spring scale from Amazon and try doing this yourself, and see what you come up with. 

https://www.alpinesavvy.com/blog/progress-capture-efficiencies-of-various-devices

Thanks for your observations and comments.

Hey John! Have you looked at Microtraxion-esque devices like the CT RollnLock or Kong Duck? They're priced pretty firmly between the Microtrax and a DMM Revolver, but I suspect the bearings aren't as fancy.

Everett wrote: Hey John! Have you looked at Microtraxion-esque devices like the CT RollnLock or Kong Duck? They're priced pretty firmly between the Microtrax and a DMM Revolver, but I suspect the bearings aren't as fancy.

The Kong Duck has no pulley; it's purely a rope grab. (i.e. a micro-ascender) (Source: I'm holding one in my hand.)

Edit: I've never seen  roll n lock in person, but that one does appear to have some sort of pulley incorporated into it.