Tips and Tricks

DSMc

Been here a while
Location
Montana
If you're pulling on the eye end of the rope, I believe this is only a 2:1. It looks like a z-rig, but the load and anchor ends are reversed, so you have a 2:1 on the harness at the lower left with a direction change (no mechanical advantage) on the pull line using the pulley on the handled ascender. Please let me know if I'm not looking at it correctly.

No. It is indeed a 3:1 because the puller is the load and is also moving. Many, many, people get that wrong.
 

Dan Cobb

Branched out member
Location
Hoover
No. It is indeed a 3:1 because the puller is the load and is also moving. Many, many, people get that wrong.
Gotcha, thanks. Makes the most sense to me (now) thinking of it in terms of the climber unweighting him/herself by the amount of force he/she is pulling, plus getting double that on the harness pulley for a total 3X advantage.

But it's only a 2:1 if a groundie, squirrel or raccoon pulls it for you!
 

Burrapeg

Been here a while
Location
Puget Sound
I don't get how the drawing is 3:1 instead of 2:1. A climber pulling his own rope over a limb or thru a fixed pulley is still having to lift himself the full amount of his weight. This is 1:1. The fact that he is moving twice the rope to do this seems quite deceptive to me. It feels like MA but actually isn't. Twice the rope is moving past the climber even if the groundie is pulling it. There may be just half his weight on each leg of the rope at rest but this changes instantly as soon as he tries to rise. He must shift his own half over and add it to the half already required on the other end of the rope, basically pulling his whole weight same as the groundie would. It is not like he magically weighs half as much suddenly. So I don't see how a climber pulling the rope himself makes this drawing's setup 3:1. We have only added a single lower pulley for MA, remembering that the upper pulley on the ascender is just a fixed redirect tied straight up to the TIP. It adds no further MA at all. Am I missing something else?
 

Dan Cobb

Branched out member
Location
Hoover
It is not like he magically weighs half as much suddenly.
In a way, it is sort of like that.

I was first looking at the diagram in the "traditional" way where you have a separate load, anchor and haul force. However, in this situation, the load (climber) and haul force (climber) are unified.

Picture a 200 lb climber holding a vertical fixed rope and standing on scales. If he pulls 100 lb of force on the rope, the scale will read 100 lb. He's magically halved his weight.

Consider the diagram with a 150 lb climber. If the climber pulls on the eye end with 50 lb of force, his effective weigh becomes 100 lb. His 50 lb of downward pull on the rope creates 50 lb of upward force on his body. Combined with the 50 lb on each leg of the pulley attached to his harness gives a total of 150 lb of upward force for 3:1 MA.

For a 200 lb climber attached to a line run through an overhead pulley, if he pulls 100 lb on the free end, he reduces his effective weight to 100 lb. The end attached to his harness also has 100 lb on it, so he can hold himself in position. With additional force, he will lift himself. So whether you look at it as (a) 100 lb of force lifts 200 lb or (b) pulling 2 ft of rope to moves the load 1 ft, it's a 2:1 MA.
 

DSMc

Been here a while
Location
Montana
It adds no further MA at all. Am I missing something else?

Yes you are, but don't feel bad, I've known of some very knowledgeable people that still don't get it.

The simplest way to verify this is to set up the 3 systems, a single line, a doubled line and the pictured haul-back system and haul yourself up each one.
 
Not my original idea because I heard this suggested elsewhere ...
After I dropped my Silky Zubat while aloft and working alone, I really disliked climbing down to retrieve it. Afterwards, I attached a cheapie carabiner to the hole in the Zubat's handle, then tied (using fisherman's knots) a discarded telephone coiled cord from that biner to the Zubat's scabboard. I found the standard headset length of coiled cord does not impede my reach. And because I can pull it back up, I no longer keep a death grip on the Zubat and will drop it anytime necessary or convenient. The cheapie biner also allows me to disconnect the Zubat so I can use it while walking about on the ground.

Great idea! Other less free options: Scuba shops sell a nice coiled camera lanyard that would be good for a handsaw. Also the construction industry is requiring tool lanyards more and more so they are more readily available.

b31d087779b539b41abd3d871ba3e972.jpg



Sent from my iPhone using Tapatalk
 
Last edited:

SingleJack

Participating member
Location
W MD
ANOTHER OPTION:
Ever drop your saw? Me, too -- sometimes on purpose. But, I always get it back … The KEY-BAK has a 48" kevlar tether. I can reach full extension with either hand. It has saved me several times over the years without injury or DQ.

 

SingleJack

Participating member
Location
W MD
Yes you are, but don't feel bad, I've known of some very knowledgeable people that still don't get it.

The simplest way to verify this is to set up the 3 systems, a single line, a doubled line and the pictured haul-back system and haul yourself up each one.
This is one really hard concept to understand. It is almost magical. I never got a hand on it until I did liked @DSMc recommends. Once I did I could slap my forehead and move on. No amount of 'splaining was enough.
To follow the lead of @DSMc and @Tom Dunlap — For years, I've struggled with how to explain why the same system can be called a 3:1, while some call it a 2:1. So, I made a little diagram that might help. It all depends, like most things, on your frame of reference. The exact same system feels like a 2:1 to a rigger on the ground and it feels like a 3:1 to a climber.
 

Attachments

  • 1-2-3.jpg
    1-2-3.jpg
    726.9 KB · Views: 58

Brocky

Been here a while
Location
Michigan
I don’t think I would want that tight of a connection, I would rather it swings away than rotate somehow back to my arm, body, or face.
 

Burrapeg

Been here a while
Location
Puget Sound
Yes you are, but don't feel bad, I've known of some very knowledgeable people that still don't get it.

The simplest way to verify this is to set up the 3 systems, a single line, a doubled line and the pictured haul-back system and haul yourself up each one.
I still need some convincing. In test number one, the climber is pulling his entire total weight with gear (let's say 200 pounds) up the single SRT rope with each pull. Now in test number two, which is supposedly 2:1 now, he runs the rope thru a pulley and back to himself, exactly halving his weight across the pulley on each leg when at rest with no pulling to climb. 100 pounds on each leg, precisely, if we assume a frictionless pulley for now. Now he wants to ascend a bit and adds a little pull to the leg opposite the saddle leg to gain some height. Here is the thing troubling me: whether a single line for SRT or doubled back to himself for MRS, the TIP or TIP pulley still sees exactly the same total weight of climber and gear, or our 200 pounds, all the time. This is a constant and no pulling of any kind anywhere in the system can change that. Whatever he does, the rope will immediately move back and forth over the pulley to equalize. So, if he has real 2:1, and can pull, say, 30 pounds over and above the 100 pounds of half-weight that is always on that leg, so that he has gained twice that or 60 pounds of upward pull subtracted at the saddle from its 100 pounds, then we have an impossibility. He cannot under any circumstances add only 30 pounds down against 60 removed up. There is no '100 pounds lifting 200'. The two legs would not total 200 pounds at the TIP at that instance. What I think he is doing, that feels like great MA, is merely moving the same 30 pounds from the saddle over to the down leg by shifting his body weight over by hanging on the pull down. Thus, instead of feeling his entire 200 pounds as he rises, like on the single line in test one, he only feels the 30 pounds he has to add to one of the equal legs and subtract from the other at the saddle, to raise his 200 pounds. Ironically, this feels actually much greater than 2:1 with 30 applied to raise 200, but is really not MA at all. He has not actually divided the total force needed at all. You have 130 pounds suddenly on the down pull against 70 remaining at the saddle at that instant, he rises and removes some rope from the loop he is hanging on to capture the progress, and the total weight at the TIP has remained his same 200 pounds the whole time, 130 and 70 for an instant instead of the 100 and 100. He has pulled 30 to gain 30 at the saddle. The 60 total difference is just that, a difference, not a total gain. It is the same 30 pounds simply moved to the other leg. And the same amount of rope is actually used, not twice the rope. He moves twice the rope at his hands only because he is also the load and is rising past his own rope moving in the opposite direction. One foot of rope moving up matches one foot of rope headed over the pulley and back down to the ground. As I see it, we may have a neat trick by splitting the climber's weight equally between two legs over a pulley for basic MRS, but I don't see we have any actual MA for the whole work accomplished. He may indeed pull twice the rope with half the force as a groundie each time, to climb, but he is also only moving half the distance each pull that a groundie could give him. His two pulls equal the single one from a groundie, both in distance moved up and also in total rope usage. How is this actual 2:1, except merely seeming to be that at the climber's hands each pull, when in fact each of his pulls is only doing half the job. Further, this means the drawing, with its one single added layer of MA with the pulley moved from TIP to saddle, is just moving from 1:1 to 2:1, not 2:1 to 3:1. We ignore the added pulley up at the ascender since it is not adding more MA and only a 1:1 redirect back down from the TIP to the climber. It may feel 3:1 to the climber himself in the third test but have we really done 3:1 overall? Only twice the rope has moved to the ground, not three times, and he has risen half the distance of rope length used, not one third. The difference involves what the climber experiences against what he is actually accomplishing in the same motion. Consider a driver going 30 mph seeing a car pass him doing 30 the other way. They do indeed pass at 60 but how far has the driver himself actually moved along the road? Or a boat moving up a river to cover 10 miles, against fast river current flowing the other way at 10 mph. The boat has to do 20 mph thru 20 miles of the water moving past him to cover the same 10 of actual distance up the river. Their experiences are valid but are not a true reflection of what they are ultimately accomplishing if they have intended to move a certain distance. As far as I can recall, this is the substance of a discussion between a bunch of experts I was privy to hear at the Sedro Woolley twin-rope thing a few years ago. Mumford was one of the group and I think he could clarify this issue much better in a video (if he hasn't already!!!). The three tests above work as they are said to and felt very convincing to me when I have tried them at times, but don't really tell me the exact amount of mechanical advantage I actually gain.
 

DSMc

Been here a while
Location
Montana
I still need some convincing... He moves twice the rope at his hands only because he is also the load and is rising past his own rope moving in the opposite direction. ... It may feel 3:1 to the climber himself in the third test but have we really done 3:1 overall? Only twice the rope has moved to the ground, not three times, and he has risen half the distance of rope length used, not one third...

So, you chose the blue pill? You are fixated on the non-moving pulley while ignoring the fact that the distance from that pulley is moving closer to the one pulling, which makes it, in essence, a moving pulley.

In a doubled rope system the climber pulls 2' of rope for every 1' foot of altitude gain. In the 3:1 referenced, the climber will pull 3' of rope for every 1' of altitude gained. The rope passing the pullers/climbers position defines the system.
 

Burrapeg

Been here a while
Location
Puget Sound
In a doubled rope system the climber pulls 2' of rope for every 1' foot of altitude gain. In the 3:1 referenced, the climber will pull 3' of rope for every 1' of altitude gained. The rope passing the pullers/climbers position defines the system.
I don't dispute any of that. Everything you said is true. However, you are defining the system solely from the climber's point of view, which is necessary in the trade since you are the climber having to do the climbing. But as SingleJack pointed out above, there are other points of view, and basically the system in the drawing is 2:1 to everybody and everything else but the climber. The groundie, the customer watching who hired you, the tree waiting for you to get up there, the rope used, everything else. The upper pulley is not a fixation to me at all; it can be completely ignored. You can just remove it and lead the rope tail right straight up through the second tip to pull up on. With the rope going up and continuing on without turning around at the fixed pulley, you clearly have a 2:1 system with the climber's weight shared equally between two supporting legs. I still maintain it is only seeming to be a sort of 3:1 to the climber when you put that tail leg through a new fixed TIP pulley and hand it back to him and then only because he rises as he pulls, using more rope than would otherwise be needed. I don't agree it is true 3:1. Both pulleys do not move, only the lower saddle one. They may seem to both move together if you totally ignore the fact that the upper one is a fixed TIP. I don't think there is any problem with this view. To the climber himself, yes, this all works as actual 3:1 and it seems fine to me if he wants to think of it like that since it gets him up the tree. I am just saying that when I look up at a climber doing this, with the rope piling up on the ground from him at a 2:1 ratio, him rising at a 2:1 rate, then I see 2:1 happening to the tree and job in hand, not 3:1, regardless if he experiences 3:1 himself from the extra rope he passes. If I am the climber, it will work for me too as 3:1, no argument there. It actually is pretty neat that it does work so well. I do it all the time, just like the drawing, in coming back in from an SRT limb walk on a ZZ/RW, with a DIY ascender/pulley thing I made after seeing the QuickRoll (and its price) at WesSpur. Works great.
 

DSMc

Been here a while
Location
Montana
I don't dispute any of that. Everything you said is true. However, you are defining the system solely from the climber's point of view, which is necessary in the trade since you are the climber having to do the climbing...

How the system works for the climber is the only accurate assessment of a climbing system. Calling it something else because it works differently in other applications is a 'yeah, but' and pointless argument.
 

New threads New posts

Kask Stihl NORTHEASTERN Arborists Wesspur TreeStuff.com Kask Teufelberger Westminster X-Rigging Teufelberger Tracked Lifts Arbor Expo BayLeafDigital
Top Bottom