Rescue Pully Placement

[genepires]

wastral is pulling a johndavidjr. wastral must be hoot on the glacier. Screaming and foaming at the mouth about trivial stuff.

 

teams of two on glaciers should always have enough rope in rescue coils to be able to rappel down to his partner in a hole. period.

 

Are you suggesting that a normal 3:1 or 6:1 be used over this canadian version of the 6:1? (for an injured climber)

[mike1]

You always put your best pulley where the load is greatest. Just do the math. The coefficient of friction times the load is drag. More load, more drag. Lower friction, less drag. Use your blue pulley first, then the Revolver, then carabiners in that order.

There's your answer.

 

W, take a pill man.

 

[snoboy]

Brian, the drop loop system is often taught and sometimes used by Canadian guides. There are advantages and disadvantages to most every system.

 

I think you've made your point that you don't think that this is the best system, but please, let's discuss the OP's question, which is "Where is the best place to put the pulley?"

 

Everybody, please, let's steer away from the flaming and arguements.

 

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My RR mentors have taught me that the best place for your best pulley is as close to the haul team as possible. Basically an inefficient pulley gets it's inefficiency multiplied at every friction point downstream... If you have access to a copy of Life on a Line 2 (cave rescue text) it has a good explanation of how this works.

[MarkMcJizzy]

I am tending to agree with Wastral, but I am also wondering if it matters? I did my own calculations on a two by two pulley system ( 4:1, U on U ), with one (1) 100% efficient pulley, and one (1) 50% pulley. The pull force is 37.5% of total load no matter if the good pulley is located at the victim, or at the tended position.

 

I mathematically bogged down doing a Z on U, but it should be easy for someone to do.

 

Sorry I can't post cool diagrams like the OP, buy it seems like the answer should be quantitatively producible, and not bogged down in rhetoric. I believe the mathematical law of position applies (I forget the real name of this law) ie: 1x3=3x1

[MarkMcJizzy]

Where L is load

1.5 is the increased force for a 50% efficient pulley

all other pulleys are 100% efficient

and 1/n is the ideal pulley system mechanical efficiency

 

((L*1/2) * 1.5 (1/3) = ((L*1/2)*((1/3)*1.5)

 

Where is this wrong?

[DavidHiers]

From "High Angle Rescue Techniques":

 

"When possible, the more efficient pulley should be placed at the input side of the pulley system".

 

From their diagram, the input is the little stick dude doing the hauling.

[MarkMcJizzy]

This is my third and last revision of my opinion. Put the best pulley at position (2). No matter what the two Brians say

 

You always put your best pulley where the load is greatest. Just do the math. The coefficient of friction times the load is drag. More load, more drag. Lower friction, less drag.

 

??? The diagram is obvious. Read what I wrote.

 

Most efficient spot for a pulley is where the load is the greatest and coincidentally where the rope is moving the slowest. Simple physics, pt (3) for those who can't read what I wrote above.

 

1) I believe that I have already demonstrated that in an ideal pulley system, that drag will be distributed throughout the system. Wether the inefficient pulley is at the end, or the start will not matter, except:

 

2) As pulley (1) tends towards 0% efficiency, the system will tends towards a 4:1 advantage

As pulley (2) tends to 0% efficiency, the system will tend towards a 2:1 advantage

As pulley (3) tends to 0%, the system will tend to 3:1

 

Therefore, it would be most advantageous to have the best pulley at position (2), keeping the system more towards the ideal 6:1 advantage.

 

3) Many pulley analysis assume that the largest source of drag will be the pulleys. In a rescue situation, this can be completely wrong. As shown in the OP, the edge will be a huge drag point. Pulley (3) could be a 12" Skookum block with bearings, and it will do no real good if there is a huge amount of drag at the lip. In this type of situation, you want your best pulleys where they can do the best work, closest to the mechanical input. If you followed Wastral or CBS's advise, you best pulley would be being wasted because of edge drag.

 

Wastral's comment that this system is stupid is also not correct. In my more than several years of climbing I have learned that

1) Jumaring up an overhang, without a pack, in Yosemite, is not easy. Prussiking with a large pack and cold hands in a crevasse could easily become impossible.

2) I have only been involved in one major crevasse rescue, but in that case we did have to get another rope down to the victim because of edge trenching. So wether a "C", a "Z", or a 6:1 is set up, it is likely another rope may have to be used.

 

Wastral or CBS can attempt to refute this, but I believe my analysis is correct

[genepires]

It is extremely likely that another rope would be needed in any crevasse rescue. (for prussiking or hauling) When would people fall in a crevasse? In the morning when the snow is frozen hard or in the afternoon when it is not? Of course it is when the snow is soft which would assume a fair bit of rope cutting through the lip. Can't climb through the lip and can't haul through it either. Clearing the lip from below could be impossible and clearing it from above runs the risk of cutting the loaded strand.

 

Prepare a sweet lip to the side to either throw down a line to climb up or haul through that if needed. Which is were the canadian system comes in. If you got a good lip, send down the loop and haul away. two strands on the padded lip are going to apply less stress to the lip than one loaded strand.

 

to bad this isn't KISS but the reality of the situation is not simple. best to learn all the tools to deal with a very complex situation.

[pinner]

Wastral; I'll take your hard cash - I always have enough coils on me on my two-man rope team.

 

As far as putting the pulleys as far away as possible, what about when you can't get very far away due to heavy crevassing? If the next hole is only 5 meters away...

 

And when you say there is the "1 normal way" that works in all situations...

 

Are you telling me my 100lb. girlfriend can pull me and my pack, a total weight of say 200lbs. out with a 3 to 1? Cuz she can't.

 

The drop loop system does work when prussiking is impossible due to some injury, but the victim still is able to help, but this ratio of mechanical advantage can of course be accomplished without the drop-loop.

 

Of course, if you've got 3 strong guys, just haul the fucker up...

[MarkMcJizzy]

From "High Angle Rescue Techniques":

 

"When possible, the more efficient pulley should be placed at the input side of the pulley system".

 

From their diagram, the input is the little stick dude doing the hauling.

 

How about a little more info about this book? I'm trying to find it at the KCLS or the SnoHo libraries. Thanks

[snoboy]

H.A.R.T:

 

http://www.amazon.com/Angle-Rescue-Techniques-Pocket-Package/dp/0323019145/ref=pd_bxgy_b_img_a

 

My library was able to get it form another library for me and I thougth it was a pretty good text. I've got it on order now...

 

Life on a Line is a British cave rescue text, but is also very good.

 

 

[DavidHiers]

From "High Angle Rescue Techniques":

 

"When possible, the more efficient pulley should be placed at the input side of the pulley system".

 

From their diagram, the input is the little stick dude doing the hauling.

 

How about a little more info about this book? I'm trying to find it at the KCLS or the SnoHo libraries. Thanks

 

I got mine from PMI. Its a good read.

 

www.pmirope.com

 

 

[MarkMcJizzy]

 

I got mine from PMI. Its a good read.

 

www.pmirope.com

 

 

H.A.R.T:

 

http://www.amazon.com/Angle-Rescue-Techniques-Pocket-Package/dp/0323019145/ref=pd_bxgy_b_img_a

 

My library was able to get it form another library for me and I thought it was a pretty good text. I've got it on order now...

 

Life on a Line is a British cave rescue text, but is also very good.

 

 

Thanks!

 

Should we buy Wastral and CBS these books too? And a pocket calculator?

 

Seriously, at what point are pulleys useless? Former YNP rescue czar Tim Setnicka (Wilderness Search and Rescue [1980]) has a study where a "Z" set up with only carabiners has a negative efficiency. At that point, single line yarding would be better

[Gary_Yngve]

3) Many pulley analysis assume that the largest source of drag will be the pulleys. In a rescue situation, this can be completely wrong. As shown in the OP, the edge will be a huge drag point.

 

We have a winner here!

[Gary_Yngve]

From "High Angle Rescue Techniques":

 

"When possible, the more efficient pulley should be placed at the input side of the pulley system".

 

From their diagram, the input is the little stick dude doing the hauling.

 

The reason for this is that a pulley behaves nonlinearly wrt force.

Mark is correct that with ideal pulleys the force, and hence the proportional force loss from friction, is multiplicative. However a pulley starts out with rolling friction of the pulley against a bearing but eventually succumbs to more friction where the pulley is motionless and the rope slides over it.

[Wastral]

If 0% efficient at pulley where you pull, then nothing happens. Thus, your best pulley must be put here cuz the amount of force transfered to the next pulley will be lower.

 

Diff subject: 2 person teams on a 60m rope:

40 feet apart on center of rope

200 feet

-40 feet

= 160 feet

divide by 2 for coils over shoulder

= 80 feet

 

If the other guy is in the hole how are you going to put a 40 foot loop down and back for 80 feet total loop length AND create a z-pulley system? Ain't gonna happen period. You have to be FAR closer than this for the drop loop system to have a chance. Around 25 feet, meaning 0 reaction time and you had better be going over Minor crevasses. If a snow bridge collapses on 25 intervals between climbers, you will BOTH be in the hole.

 

Diff subject: If you are going over a glacier with a 100lb girlfriend and you are seriosly injured and can't prussic out, then her building 3:1 won't work due to inefficiency and a 6:1 won't work due to rope stretch. She won't have the strength to stretch the rope pull some up and move the prussic down the rope to hold the stretch.

 

Besides majority of drag is from the rope drag over the lip not the pulley system.

 

At least there aren't many real glaciers in Washington State for you guys to fall into because if you were on a rope team of 3 you would be trying to set up 3 different systems and by the time you got it figured out, the guy would be frozen to death in the hole. This is a very real concern, not just sarcasm. One should think about it before the crap hits the fan, talk it out in the group first.

 

Brian

Edited February 13, 2009 by Wastral

[Gary_Yngve]

put the pulley on #2. What matters is most is the amount of rope running through the pulley, not the weight held by the pulley.

 

Highschool physics says the exact opposite. Ff = K * Fn

Friction is proportional to the load.

 

Sure there might be some nonlinear effects eventually, but normally I think of nonlinear effects arising because of drag, heat, deformation, etc., which I think would be insignificant in the realms we're dealing in.

 

Am I missing something?

[Gary_Yngve]

If 0% efficient at pulley where you pull, then nothing happens. Thus, your best pulley must be put here cuz the amount of force transfered to the next pulley will be lower.

 

What pulley system are you talking about here? A classic Z is 1-1 if either pulley is jammed (mmm.. grape!).

 

I'd have to diagram it out for 5-1, 6-1, compound, complex...

[Wastral]

Any pulley system.

 

If the input pulley(where you pull from) has a 0% efficiency(stuck, not moving), then 0 force gets applied to the second pulley because the first pulley is not rolling, thus the rope would be sliding. Thus, horrible efficiency.

 

A good example of this is the "revolver" pulley on a carabiner that they sell in local shops. It will spin under light loads, but under a real load the shaft bends and it locks up, making it a horrible idea to use as a second "pulley" for crevasse rescue.

 

Brian

[spotly]

You've continued to imply that anyone who would consider using a drop loop is an idiot. Let me remind you that the OP was not about systems, something that has been pointed out to you several times...it was about pulley efficiency. If I had a 6 inch length of rope that I used as an aid for discussing how a rope is made, would you think that idiotic too - after all, who the hell could possibly climb on a 6 inch length of rope.

 

You think that discussing something here implies that the same discussion would take place on the mountain!? Then you go on to say the "One should think about it before the crap hits the fan, talk it out in the group first." WTF - it's like listening to Tweedle Dee and Tweedle Dum!

 

At least there aren't many real glaciers in Washington State for you guys to fall into because if you were on a rope team of 3 you would be trying to set up 3 different systems and by the time you got it figured out, the guy would be frozen to death in the hole. This is a very real concern, not just sarcasm. One should think about it before the crap hits the fan, talk it out in the group first.

 

You've made a few good points as it relates to the OP but then you go off on this totally unrelated tangent. Try some ginko or something for that lack of focus.

[Gary_Yngve]

If the input pulley(where you pull from) has a 0% efficiency(stuck, not moving), then 0 force gets applied to the second pulley because the first pulley is not rolling, thus the rope would be sliding. Thus, horrible efficiency.

 

I'm confused by your definition. By 0% efficiency do you mean that the rope is sliding around the pulley or that it is not moving at all (as if a knot in the rope)?

 

If you have a classic Z pulley and put a knot in the rope just upstream of either anchor pulley or floating pulley, the system reduces to a 1:1 either way.

 

Regarding the revolver pulley, my guess is under a constant velocity, at either pulley position would be equivalent. But with acceleration, it might be worse as the floating pulley.

[Gary_Yngve]

You've continued to imply that anyone who would consider using a drop loop is an idiot.

 

I think he's trying to say that pulley efficiency when using a drop loop is the least of your concerns.

 

It's like if you're using a tandem prusik.. do you sit there and argue whether the longer one gets clipped closer to the spine of the biner than the shorter one or vice versa, or do you say good enough and get stuff done.

[Wastral]

Efficiency as regards to pullies is as others have pointed out, High School physics.

 

Ok background: 2 types of friction

 

1) Static friction

2) Rolling friction

3) Static friction is always greater than rolling friction

 

When talking pulley efficiency, carabiner or pullies with or without bearings, we are talking about rolling friction. Static friction is when the system is at rest. Static friction is not all that big of a deal in Crevasse rescue because the rope is a dynamic rope and stretches allowing different parts of the system to move at different speeds at startup, obviously if you pull at a constant speed this is a mute point. But, one never pulls at a constant speed. You pull in herks and jerks.

 

In otherwords, the guy in the hole is not moving even though you are pulling on the rope at the begining of your pull cycle. Thus, you jump past the static friction problem at pts. 1 and 2. Where static friction is a concern, is at pulley #3 where the force is the highest.

 

A bearing pulley will ALWAYS have far lower static and rolling friction. Thus, why I stated that if you yave two pullies they should be at points 1 and 3. Point 1 to overcome efficiency ripple. Point 3 to overcome Static friction startup problems.

 

Brian

PS. I have run into lots of Tweedle-de and tweedle-dumbs.

PPS. I put in my replies because some completely ill informed guys replied to my posts trying to postulate that the drop loop system is actually rational. As I rationally proved, its not. Didnt see you castigating them, since you agree with them for some reason which you never give. Just think that reading my posts is like talking to women. I reply to more than 1 post at a time since I dont check every 5 minutes for replies.

Edited February 15, 2009 by Wastral

[genepires]

Are you saying that the canadian AMGA is tweedle dumbs? Cause they use they dropped loop system for hauling out injured victims from crevasses. They must be completely ill informed.

 

Mark Houston (a UIAGM/IFMGA the international guiding certification) also goes through why the dropped loop is a good tool to have for a rescue situation. Not the only tool, but one of many that people should know and practice before going out there. (in his alpine climbing book) Yeah, what do these people know about crevasse rescue? They have only been doing it for 20 plus years and a real interest in doing it right.

 

 

Along with research from people who really study the physics of it, like the company Rescue Dynamics. They have an article about pulleys and use. http://www.rescuedynamics.ca/articles/pdfs/Pulley3to1.pdf Their studies (for efficiency) have shown that the single pulley is best used on the pulling end in a 3 to 1. Not a big stretch to assume that it would be the same for a drop loop 6:1 since it is just a 3:1 pulling a 2:1.

 

And Gary Yngve, you are not missing something. I was misinformed about my physics as you obviously are superior with. I was told about the single pulley use from a AMGA head instructor but I was wrong about the physics of why. I thought it was more about heat generated from the amount of rope rubbing past. (my own hypothesis) I defer any physics knowledge to you.

 

I have met a tweedle dumb and his name is Brian. Is there a sexist comment in his last PPS? "Just think that reading my posts is like talking to women."

[MarkMcJizzy]

 

If you have a classic Z pulley and put a knot in the rope just upstream of either anchor pulley or floating pulley, the system reduces to a 1:1 either way.

 

 

No. A knot at position (2) renders a 3:1 to 1:1. A knot at (1) renders the system 2:1 instead of 3:1. It really shouldn't be that hard to visualize.