Tips and Tricks

Tom Dunlap

Here from the beginning
I wish that I had links to all of the times the doubling on a DdRT TIP has been discussed.

There actually is a time when the climber's load doubles. During the time that they pull down on the rope and pull up on the climber happens.

'Variable' is the key!

Besides...a TIP should be chosen to have a substantial safety factor. If you're even thinking that the difference between 2:1 and 1:1 is an issue, other than for coffee table talk, your TIP is under strength by a LOT :)
 

Fairfield

Well-Known Member
The big difference with Ddrt and SRT basal tie off, is when you go to move with Ddrt up or in you need 101 lbs of force to move 100 lbs. meaning the high point will see that force doubled (for the most part). With SRT basal tie off unless the line is doing a 180 back to the tie off it wont see the full force on the high point. The more the angle is opened up at the change of direction(high point) the less the force will be. Like Tom had stated there are other physics that apply also, but the bare bones of it is the above.
 

Adam_P

Active Member
[ QUOTE ]

There actually is a time when the climber's load doubles. During the time that they pull down on the rope and pull up on the climber happens.


[/ QUOTE ]

I never knew that. I've been doing more basal anchor stuff lately but still primarily cinch. Knowing that does take the edge of my basal paranoia... just a bit.
 

Jeremy9

Member
I don't know but that doesn't sound right to me. I don't think your ever doubling your load in a Ddrt system. It should only take 50 pound of force to move a 100 pound, if your taking friction out of the equation.
 

jomoco

Active Member
[ QUOTE ]
I don't know but that doesn't sound right to me. I don't think your ever doubling your load in a Ddrt system. It should only take 50 pound of force to move a 100 pound, if your taking friction out of the equation.

[/ QUOTE ]

You've got your equation upside down, spatially speaking.

jomoco
 
[ QUOTE ]
The big difference with Ddrt and SRT basal tie off, is when you go to move with Ddrt up or in you need 101 lbs of force to move 100 lbs. meaning the high point will see that force doubled (for the most part). With SRT basal tie off unless the line is doing a 180 back to the tie off it wont see the full force on the high point. The more the angle is opened up at the change of direction(high point) the less the force will be. Like Tom had stated there are other physics that apply also, but the bare bones of it is the above.

[/ QUOTE ]

So a 165# climber pulling down on one leg of a Ddrt system would have to exert 166# to lift himself? At that instant in time he "weighs" 331# ? I don't think so. First of all, he weighs what he weighs. The two lines are sharing the load, whatever it is. As he pulls down on one leg, he is relieving the load on the opposite leg. I agree there will be some fluctuation due to friction, sudden pulling, etc, but he will not double his weight unless he pulls mighty hard, mighty fast.

My initial response was to someone saying that in Ddrt, the TIP ALWAYS sees double the load. I disagreed then, and still disagree now. We are not talking dynamics, but static.

Dynamics are most hard to figure, especially in climbing. If the climber weighs 165#, then the load on the TIP is 165# when the line(s) are vertical, whether he has 1, 2, or 6 lines bearing his weight. How much load is exerted on the TIP, however, when the climber is out on a limb, and the line is at a 30% angle from the TIP, where horizontal side loads come into play as well? His vertical load has dropped, but the side load has increased dramatically. Most smallish TIPs handle vertical loading quite well, but a severe side load could easily compromise a 3" TIP, especially in some species.
 

Tom Dunlap

Here from the beginning
Get a fishing scale and a piece of wood to substitute as the climber. Drape some shoelace through the hook on the scale and see for yourself.
 

TreeCo

Well-Known Member
[ QUOTE ]

So a 165# climber pulling down on one leg of a Ddrt system would have to exert 166# to lift himself? At that instant in time he "weighs" 331# ? <font color="red"> </font> First of all, he weighs what he weighs. The two lines are sharing the load, whatever it is. As he pulls down on one leg, he is relieving the load on the opposite leg. I agree there will be some fluctuation due to friction, sudden pulling, etc, but he will not double his weight unless he pulls mighty hard, mighty fast.

[/ QUOTE ]

You're right.

Scary to see such a misunderstanding of basic physics being propagated.
 

TreeCo

Well-Known Member
[ QUOTE ]
Put it up on a scale like Tom said see what you get.

[/ QUOTE ]

How do you get the scale to pull itself upwards on the tail of the rope as does the climber?
 
Surely we are having a misunderstanding here! Surely you don't believe that a climber's weight is doubled a the TIP just because he is using Ddrt? Again, we are not talking about dynamics, but static conditions. Hang anything you want, from any scale you want, with as many lines as you want, and the scale will read the same, excluding excess line weight of course. By the token being presented here, does a 150# climber, using 3-strand rope exert 450# on the TIP via SRT? Gawrsh, if he were using Ddrt, he'd put a whopping 900# on the TIP (150# x 3 strands of rope x 2 legs).....I believe someone's off course here.

O-o-o-r-r-r.....does a 200# fellow standing on a bathroom scale weigh half as much if he stands on one foot?
 
[ QUOTE ]
Tom, time to dig up some of those old threads and blow the dust off of them again.

[/ QUOTE ]

Might dig out the old spectacles and physics books while we're at it. And post some diagrams to make sure we're all on the same page.
 

Tom Dunlap

Here from the beginning
Leave the books on the shelves...get a fish scale and fake-up a mini-climbing system.

This discussion has gone on for many years. Until you see it with a scale or dyno its hard to understand.
 

Jeremy9

Member
I don't see how a fishing scale would work? The question is not how much the climber would weight hanging, but how much load you put on your tip has you move up the rope. If you set up a mimi set up you would have to add outside force to the system to make the climber go up, that would give you false reading.
 
[ QUOTE ]
Leave the books on the shelves...get a fish scale and fake-up a mini-climbing system.

This discussion has gone on for many years. Until you see it with a scale or dyno its hard to understand.

[/ QUOTE ]

Okay, when our 7-year-old was born, (at home), we used a digital fishing scale to weigh her, suspended in a blanket/sling. Suppose I had made a loop sling to run from the sling she was in up to the hook. Would she then have weighed 14#, versus the 7# she actually weighed? What you are failing to see is the gist of the discussion. When the climber is on a Ddrt system with a friction hitch, he is on a closed system that forms a loop. Adjustable loop, but still essentially a loop, and his weight is hanging on TWO legs of rope. When on SRT, the climber's weight is hanging on a single line. The load exerted on a rigging point, TIP, or any other point is no different if the load is SHARED by any number of legs of line. All the 2:1, 3:1, etc systems require one leg to be kept out of the equation to do the pulling/lowering/etc. Once more, a Ddrt system IS NOT the same as a 2:1, because it forms a closed system, with each leg sharing the load. Only if one end is fastened to an anchor, and the climber suspends his weight from the other leg of line does it place 2:1 on the TIP, as in basal tie SRT.

Again, I think a diagram would be helpful, as I can't believe this discussion is even taking place. My first post in this thread was in response to Fairfield's statement......"As for Ddrt the high point is always under twice the load/ force being pulled on it." This is simply not true. At times it might be under four times the load, but the same applies to SRT. The key word I was addressing was ALWAYS. I disagreed then, still disagree today, and will likely disagree tomorrow as well, as it ain't so. The only way to use "ALWAYS" in reference to load bearing on the TIP, would be when the system is static, and in Ddrt, the load on the TIP while static, is 100%, as the climber is hanging on a closed loop of line.
 
I like to set up my climb line using the principle of mechanical disadvantage, that way when I let go of the rope I fall up the tree.
 

Fairfield

Well-Known Member
Not sure how I got off track on this and what I am trying to say but reading back I did. For Ddrt when static yes, the TIP is holding only the weight on it no more. But when the climber goes to pull them self up (saying that they are in a free hanging spot) the TIP would then see the load doubled. Im not saying that if the climber has his feet pushing up on something that it wouldnt change the force on the TIP. The always in my statment is wrong should have said it diffrently. Well I am still human.
 
Glad you're coming around, but I still disagree that the TIP sees the load doubled when the climber pulls himself up. If another person pulls him up, the load is doubled. But if he is pulling himself up, how can he double his own weight? As he pulls on one leg, weight is transferred temporarily, and so for a short period of time, the load is not equally shared, but aside from sudden pulls, etc, his weight is still the same. It's basically the same as doing a chin-up. The bar "fells" the same weight whether the person is hanging by one hand or two, and this load is constant aside from the dynamics of how fast the person chins himself. The load is also the same throughout the cycle. Would the bar bear more load while the man is hanging, while he is at half-chin, or at full chin? He weighs what he weighs.....

To say that Ddrt yields doubled load as the climber pulls himself up, is to say that choked SRT doubles as well when the climber pulls down on his ascender. (Both bear 100% of the climber's weight, and both scenarios involve physical effort to lift the climber). No one thinks that, do they? So why think that Ddrt yields double load when the climber is pulling up?
 
Top