OK.....Let's Get Into The Meat Of SRT !!!!

[RescueMan]

Hitch for descent?!

While I don't have the experience you guys have in DdRT climbing and descent with Tautlines or Blakes, I would have to agree with Jeff Jepson (The Tree Climber's Companion) that it's not possible to safely descend on a static line solely on a friction hitch.

With a doubled rope slung over a crotch or a even friction-saver, most of the climber's weight it dissipated in the friction of the rope moving over it's upper support point which leaves far less than half the climber's weight to be controlled by the friction hitch, making it possible to do a controlled descent (this is also why an autobloc hitch on the brake side - below - a figure-8 rappel device is so easy to control). In addition, because there is two feet of rope moving through your friction hitch for every foot of descent, this gives a 2:1 friction advantage.

On a single static line, all the climber's weight would be on the friction hitch making the hitch grab sometimes too well and be difficult to release. When it does release it tends to result in sudden uncontrolled acceleration and any attempt to stop the descent can result in the melting of the hitch cord and either fusing to the mainline or severing.

Heat-resistant cords typically are too slick or too stiff to work well in friction hitches (the size ratio and the stiffness ratio of the hitch cord to the host cord is crucial to proper function).

Even using a prusik hitch as a back-up above a descent device has resulted in a number of deaths and near misses among very experienced climbers and cavers (Oh, BTW MasterBlaster - don't ever call us cavers "spelunkers" - that's the term for amatuers!).

I had thought of offering a $20 prize for anyone who could come up with a hitch that would SAFELY work for descent on a static line, but I don't want to be responsible for getting any of you killed.

Climb safe and land on your feet,
- Robert

 

[Lumberjack]

One reason is because in other fields like caving, there have been many cases where they paniced and squeezed the knot harder (instinct), making them dirty up the cave with their inards.

Another is the extreme friction from the knot supporting all the climber weight.

Probably some more.


Carl

 

[Tom Dunlap]

This afternoon I spent some time at my favorite mountaineering store. I wanted to tap into their knowledge and look at some other friction tools that I'm not familiar with. In short order, three of the sales people were involved in the discussion. I showed them how a Distal with a slack tender worked. They were impressed. This shows that there is room for arbos to teach othre rope people a thing or two.

Making blanket statements is a challenge to creativity. Think back to how arbos have pushed their skills in the past few years. There are many arbo-specific tools used now. Also, many knots have been tweaked to meet our needs.

With some thinking and sharing I believe that we can find a solution to this quest. I might just come back and hit you up for the twenty

Tom

 

[TheTreeSpyder]

Tom on that site you posted at TreeB*zz (site i use as this expansion, sometimes differint explanations, secret supply to post here etc. ) as i was scurrying around; i found this real neat breakdown from Bruce Smith's On Rope Catalog that shows for free these detailed systems seperated like in his and Padgett's monumental "On Rope" vertical roping's "bible" to so many rescuers, mountain, ice climbing, riggers, military etc.! A fairly cheap must have for really understanding the challenges of friction and camming systems and more, Sherrill #16201 IMLHO!

i think it will puts forward a lot of terms of systems, and the assumed elements of those systems to be able to talk and be on same page etc.(not as bad a jargon as SWL your SRT but TITS ain't a PITA, just like in DdRT, See ANSI-like we talk!). This SRT stuff is a lot more invisionable, with systems drawn out, and them talking about choosing and maximizing a system to a specific body type even!!

The Same Site (On Rope) , has a list of Free 20 DownLoadable Guides to Working with Ropes inways that may be new and stretch a lot of understandings. If ya couldn't a budget the book this round like me. (If it wasn't already here doggy eared), maybe ya can afford these; the price is certainly right!

This page from there claims "A Double Bungee RopeWalker is the Fastest and Most Efficient Rope Climbing System in the World" and displays it in detail, with all componenets named, shown etc. Along with their 2nd pick apparently the Mitchell system. i think either would deal with inertia better than a stop/start 'frogging' and with right style make a smooth motion that carries through to the next, rather than needing to be started again. Or as i say, so you don't have to re-inertia-lize the system, in my whimsical, satirical mental pix. i believe this componenet (inertia) can help increase system of ascending efficiency greatly, if ya got the smooth continuous lift style right.

 

[TimberMcPherson]

Okay tree machine emailed me this. He is currently cruising New Zealand and isnt able to play with you guys!

"Could you do me a major favor? Could you drop a line into the 'Meat of
the SRT' thread and tell the guys that I'm feeling a great deal of pain
NOT being able to contribute to that session? The other threads I can
survive without, but not being part of the SRT thread is just killing
me. I would really appreciate you doing that."




My Job here is done

Timber

 

[Lumberjack]

Just bumpin this thread back up. It seems we are starting the discussion up again.

 

[John Paul Sanborn]

It also helps if you can acquire a "high tech" line with a high heat resistance. Vectran, technora, and nomex come to mind.

Look at the wear charecturistics of the product.

I've been told by a treeman218 has told me that that some technora will loose it's strength rather quickly, and should not be used for human suspention.

 

[RescueMan]

High Strength Cordage

I posted this link on another thread. Check out this report on the characteristics of the high-tech cordage:

Comparative Testing of High Strength Cord

- Robert

 

[RescueMan]

Earlier in this thread there was a lot of head-scratching about why DdRT is a 2:1 system unless the groundman hauls the climber up.

This example might help:

You're driving a 2-horse wagon and you get stuck in the mud. Fortunately you have some rope and a pulley and there's a tree just ahead of you. So you attach the pulley to the tree, tie one end of the rope to the wagon, run it through the pulley, stand next to the wagon and pull while the horses are straining at their traces. The wagon still doesn't move. You're pulling 1:1, through a stationary pulley (TIP or change of direction).

Then you get a bright idea. You climb up on the driver's seat of the wagon and yell giddup to the horses while you brace your feet against the footboard and pull on the free end of the rope. Now the wagon pulls free. Without changing the system, you've turned it into a 2:1 because for every pound of pull on the free end, your feet have to press into the footboard with one pound as well. If your hands are pulling with say 100 lbs and your feet are pushing the wagon with 100 lbs, then you've created a 200 lb force to assist those tired horses.

The wagonmaster can be a tree climber, and the pulley can be a crotch. For every lb you pull down on the climbing rope (DdRT), you lighten yourself (lift your weight) by one pound. This gives you two lbs of lift for every pound of pull. If the groundman is doing the pulling, it's like standing beside the wagon - 1:1!

Is that any muddier? Or are your horses still stuck?

- Robert

 

[MasterBlaster]

Good explaination, Rescueman!

 

[Tom Dunlap]

Finally a better way to look at DdRT MA!

Thanks a lot!

Tom

 

[TheTreeSpyder]

Ummmmmmmm; then if there was just a single line; and you pulled 100# with arms (first example?), then there would be 0 force on feet and you would have a 1:1, just pull 100#?:alien:


i would think that you needed that attatchment to the wagon to move the wagon, else you would just pull out of it, so that part of the loading does not give the 2:1?

i think the magic trick is that the pull line in the first example; is just a pull redirected off of the pulley; pulley/hitching/tree takes on 2x force of pull; you pulling on one leg; and the wagon pulling on other. The system is 'open' to allow the extra force into the equation.

Sit in the wagon and pull(close the open leg); the system has now become self contained; it is not 'open' to other forces, there is just redirect and load, the pulley now takes on just 1x load; because the system is closed-other forces are not taken on. Now the 2x function is on the load; as the pull point also a load hitch point, serving 2 seperate functions at once. Grabbing both lines at once and pulling would give speedier 1:1; grabbing just the one not tied to wagon, gives 2:1; but you have to pull at 2x speed of wagon to maintain helpful force. So your pull position, also is a load attatchment point, then the tied end is another, fer 2x; i think the confusion is not seeing the duality of that service point of pull in this system; not giving it that 'count' on the pulls on the load.

Now the hardest part would be to get it started; if it won't budge, i might try to tie down the pull end tight as possible to the wagon, and bend it to the side sharply, then start pulling quickly as possible if that high leverage force fed into the 2:1 werked. Failing that i might (with an extra leg of line or extension on pull end), untie the free end from the wagon and try to take as low a friction redirect off the wagon back to the tree for 3/1 - friction; slight sweating/leveraging of line to start still appllicable IMLHO. Hey; a lil'guy needs extra help!

At least that is the way i've scrunged around in this self taught hodge podge dance and have come to see it.


Orrrrrrrrrrrrr sometin'like dat!
:alien:

 

[RescueMan]

because the system is closed

You're on the wrong track here. Both systems are "closed". For every action there is an equal and opposite reaction.

In the 1:1 standing on the ground beside the wagon, of course your feet have to resist your pull with the same force, but they're trying to turn the Earth. This IS a closed system and your force will change the rotation of the Earth, but not so you'd notice.

In the 2:1 on the wagon, the system is likewise closed but the force applied in reaction by your feet WILL move the wagon. The only difference between the two examples is that the wagon is a lot less massive than the Earth. For all practical purposes, you can discount the effect on the Earth.

When you pull on your DdRT climbing rope while hip thrusting, you're imparting an equal force in both directions, up on one side of the rope and down on the other. If you're at all lighter than the Earth, you'll notice a 2:1 advantage.

- Robert

 

[TheTreeSpyder]

i'm sorry; i don't see it sir......... (edit-swooped on posting by Dan speed typing, speaking to RescueRob)

There is an opposite and equal reaction to everything; that is why i argue with MM so much; tell JP the short side of things......

i look at the leg use in your examples to provide extra muscle and extension per pull; but no power conversion without forsaking the pull distance for more power. i think the Equal and Opposite reaction is of course true; but will be in all examples

i believe there are 2 line pulls on the load, powered by one line pull to make the 2/1.

If you had the 2/1 setup; and you grabbed both lines at once to pull (like footslocking up a doubled line like it was a single one); you would have 2 lines pulling, but be powering 2 lines at once, so you would have 2/2 :: 1/1?

Or no pulley, just a line tied to tree, to draw yourself in(sitting in wagon); would be pulling 1 line, that pulled once on wagon for 1/1; irregardless of foot position IMLHO. i don't think that pushing with feet as you pulled a 1/1 would give MA of 2/1; so i don't think that is the deciding factor. If you weren't pushing with legs on wagon, or connected some other way (weight, seat belt etc.); you would just pull yourself out of wagon; 2/1 , 1/1 ?

i beleive it is simply, that you are pulling 2x as much line as motion achieved; it does this by you having to shorten each leg of line 1' to advance wagon 1'. If you were cranking a hand winch, bolted to the wagon it would have inalterable placement; yet the MA beyond what the winch gave would be from the line lacing i think. Cuz you would have to give up distance to get power all ways and always; dems da rulez! ...As i'm sure you know .

By closed system i mean that all lines terminate at support and load, no matter how many legs of line 1,2 or 15; the support will only incur 1xload; until you 'open' the system to more pulls/pushes IMLHO.

i think hip thrusting reduces load and alos friction on support, doesn't give MA.

i do enjoy your universal view of drawing the Earth etc. into the equation; but do not find such existential philosophies/physics to be a determinate factor here; but rather constantly present; thereby not lending definition.


Now, jest to start more trouble; i'm picturing big stagecoach wheels on small axles, so perhaps getting out and turning a wheel by hand(depending on design might just turn one side at a time) for some help would be best; by taking leverage over the rolling resistance of the axle/wheel; especially one without bearings; or other frictional disadvantages IMLHO; especially noticeable riding up any incline or stone in the way; also lightening the wagon.

 

[RescueMan]

TreeCo said: The only problem I see is that the climbing system only looks like a 2/1 ma system when in fact it is not.

I understand the confusion around this, but DbRT is a theoretical 2:1 MA system, just as the wagon system was.

And you bring up a lot of valid points that complicate the actual climbing system, mainly the effects of friction, which in this case are actually an asset.

But try hip thrusting on a single static line with your feet and hands in the air. You can't do it. What allows you to lift your weight at the hips is that you are pulling down with an equal force (equal and opposite) with your arms. But the pulling down with the arms doesn't at first advance the rope (it's like you're pulling against a fixed line) until the hip thrust sufficiently unloads that side of the rope and reduces the friction enough for your hand pull to advance the rope downward. When you weight comes back down on the TIP, the friction allows your hand to easily hold the advance until the hitch is moved up.

The less friction at the TIP, the more the load is equally shared by the arm pull and the hip thrust. If you had the rope through a ball-bearing pulley at the TIP, it would become obvious that the arms and the hip are each doing half the work. And if you're strong enough to pull half your weight, you could raise yourself on a frictionless TIP with your arms only. Which makes it a theoretical 2:1 MA system.

- Robert

 

[TheTreeSpyder]

Hmmmmmmmm In My LIL'LowlyOpinion;

Not to be more argumentative than usual...........

When i read MA; i generally think of increasing power/losing speed or the reciprocate of losing power but gaining speed; in excess to the effort expended speed x power.

i see leg pushes, hip thrusts, hand pulls etc. as effort expended; perhaps more effiiciently sometimes but effort expended to get more lift/pull/push etc. That extra comes from calories consumed, less losses to efficiency of use, 'machine processing' etc. to give you the energy to perform. This energy came from the sun etc.

A DdRT would be a 2/1 theoretical MA, less friction. The {2/1 - friction} will equal the expended work force (effort x distance applied); disallowing rope stretch, flexing of support etc. Cuz, play don't work! And if ya look at the leveraging at just 1 degree off of straight, jsut the smallest imperfection in a perfect balanced/straight machine gives the greatest dynamic loss per degree of flex etc. Bt that also means that those subtle nuances polished out as close to perfection as possible makes one race car etc. faster than another, one system silkily, smoothly balanced, to a ballet of gracefull power.

i think these things are all prevailing, and that olde Greek Phycisits were also the Philosophers and tried to show these dynamics as so prevailing and ruling on this Earth; that they defined them as consistent in both fields at once.


Orrrrrrrrrrrr something like that!
:alien:

 

[Kneejerk Bombas]

Originally posted by TreeCo
Try this......tie a rope to a 50lb weight......put the rope over a limb and try to raise the weight into the air. The friction of the crotch will make you have to pull way more than 50lbs.

Dan

It's easy if you think of it like this:

If you stand on the ground and pull 50 pounds, you pull one foot of rope to advance the weight one foot. That's one to one.

If you are the weight and pull the rope one foot, you only advance a half a foot. That's two to one.

Like Rescue guy wrote, the friction can act as an advantage like in body thrusting, or a disadvantage, like in pulling 50 pounds up from the ground with the rope over a limb.

If I read Spyder correctly, about the same calories are burned thrusting, wether you thrust or not. It seems easier to thrust because you are using different (and bigger) muscles.

 

[TheTreeSpyder]

Nahhh Mike, i think more calories would be used, but perhaps greater efficiency etc., single strategy to serve several purposes etc. by body thrusting; that is the defining element to me.

Friction costs your efforts on lift, but eases efforts on hold/lower in trade; it can also isolate/buffer how much line needs prestretched, help to hold a sweated in force, but limit amount of dynamic shock absorbing or energy storing line in exchange. A trade off/ rearrangement to everything. Strong or flexible temper in metals, deadwood (not decayed) can be stronger, less flexible for homes etc.; a Live Oak seems to me to grow slower but tougher in trade than other of our oaks, with a local water oak on the reverse end of the scale. i use the 'reptilic scaliness' of the bark as a thumb rule for defining strong/slow, weak/fast in local trees.

Law of Conservation of Energy (m'Lady properly termed this for me years ago): The calories thing was a comment about energy/effort put into something for more power x travel vs. redistributed power x travel from 'deflecting' given efforts off a machine to gain more power or travel (but not both at same time) from the output of machine. If you expend more energy, that is not MA; it might be more strategic but not MA as i understand it. MA gives more power or speed (but not both) without extra energy and takes some kind of simple machine to create. The machine takes the finite/set amount of workforce units (power x travel) you create by effort , and rearranges them to more power x less travel or less power x more travel; but less frictional losses (as a cost of conversion) the power x travel output by the machine equals the original workforce units you expended. The work energy is always converted, never lost or destroyed; even from calories to person to line to work, it is all accountable, a set/finite amount.

Energy is never lost or magically appears, it is a finite amount just converted to your use, as it rolls on through to something else.
Gasoline is favorite pruf i devised, by the high energy that has been stored for millions of years and never lost, originally coming from vegetable calories (units of heat energy); that came from the energy of the sun etc. It all has ineficiences; but is a traceable set amount, if you knew how to see it, even the inefficiencies of different , individual frictions and digestions have a set amount in the formulae that all adds up to what was initially expended etc..

Every machine is a transmission. You get power or speed out of a set amount of workforce units made by the motor source. Downshifting or stepping on gas gives more power, one uses MA, the latter more energy. In this way you get power (for takeoff) or speed from the same source, but not both; without adding energy. That is why better, more efficient tools are so good, the energy is a finite thing, and better tools squeeze more out of that. The dynamic changes per degree increase so much as you get close to perfection, that they become a silky feel and smoothness that catches your eye etc., as in all things.

i think the leg on the wagon example used more energy and served as necessary mount on wagon for pulling force, but is not MA by these exam-eye-nations.

i also think that you could body thrust or 'kip' up, and catch on hands without arm pull if you chose and fit enough; prolly wouldn't be very smart! i get that from gymnastics, enough explosive force with heavier legs and lower torso alone can overtake inertia of the rest of yourself to give lift; but it would be more efficient to pull with arms too, and take advantage of the force as it died down, but still enough upward force that arm lift would not be against whole body weight. In DdRT, the 2/1 arm pull wouldn't have to fight as much friction, as it wasn't facing as much wieght..

DdRT is 2/1; 2xpower at half speed - friction; friction of branch, bushing pulley, bearing pulley etc. grow more efficient as less friction is involved, or gaining leverage over present friction with larger sheave. Speed being considered faster if you have to pull 2 feet as much line in the same amount of times that load moves 1 foot. But never quite reaching 2/1, there must be efficiency loss, there must be friction as a cost of the machine use/conversion, for there can be no perpetual motion machine, that could run forever off the same energy source due to it's efficiency and force funneled back into itself to keep going. Just as a pendulumn will slowly come to standstill.


Orrrrrrrrrrrrrrrrr something like that.........
:alien:

 

[NickfromWI]

Dan, I think you're on to something here. People often tout the 2:1 MA as a reason why DDRT is better than SRT. It's not so much that there is a mechanical advantage...it's that you're unweighting the rope before you pull up the slack.

But still, you can't do this with SRT.

love
nick

 

[Lumberjack]

I am growing fond of DdRT. I am not sure if it is just because it is new to me of what, but I like it. I am using UT, because I still have an eye to eye cord from when I first started, and a VT with a micro pulley. I havent used it too much yet, but I might do something like TJ setup. The RADS is cool, but I like new things. Someone said they wondered what would happen if someone learned SRT and then DdRT. I am just tryin it out, but I like the friction hitchs.

Another thing on SRT. When climbing with RADS (through a e-mail with Rescue Man) is to put an etire on the upper ascender. That might be the ticket to make climbing with the RADS (not towing it up) feasible.