SRT PSP and other acronyms...

[Cupressus]

Hey all,

As you know, I'm a rank noob when it comes to SRT. Finally saw the light trying to horse up a Ghost Pine in GV on my familiar old DdRT. Hello, tendonitis! I have exactly one short, slow and low climb on my RW, but I've been thinking through some of the potential issues I might come across. I will probably shell out for the SRT manual once I've got a few more jobs in the bank and the rent is paid, but for now, I'd appreciate some help.

1. My understanding with SRT is that SOME of the appeal is in not having to isolate your PSP with the throwline. so how much deflection on small bits and pieces is tolerable in the system?

I used an old-skool SRT setup the other day to ascend a big pondo, and the rope ran over the outside of the canopy, through my psp and back down the outside of the canopy. This lent the system a certain amount of "bounce" and gave me a few small pieces of breakage (snapped twigs the rope had run over) to clean up on my way to the top.

Are guys spending some time isolating for SRT as well?

2. On the physics of the thing: The PSP on a basal-tied SRT line supports 2x the climber's weight. How does that number change when there's an angle greater than 0* between the two legs over that PSP? For example; climbing with Bix the other day, he set his line and tied in not at the base of the tree we were climbing but at the base of a neighboring oak about 50' away. I'd say the angle was like 60* or so?

I know from playing with RA rescue setups that it's relatively easy to deflect a taut line in the center - deflection can be used to haul a victim without setting up mechanical advantage using hardware. Does that effect translate in reverse here? In other words, does a wide-angle of tie in mean the PSP is supporting a fraction of the climber's usual doubled-weight?

I wish I could draw what I'm saying. Maybe time to play with MSpaint a little bit, huh?

Thanks, SRT club!
C

 

[Colin]

PM sent.

 

[Colin]

Hello,
I would caution using a remote (other tree) as a basal anchor. Look at the angle at the PSP created by the rope running to the anchor and PSP in the other tree. Bisect that angle and that is for the most part where the force is being applied. If the remote anchor is a fair distance away from the tree that you are working in, the forces could be working against you, as in not compressing the trunk on the tree that is being worked. You are actually create a fishing pole effect. Same principle as in rigging.
That number does fluctuate based on the degree of angles at the PSP, but it also transfers the force to different directions. I like to use the term multiplier instead of saying straight out 2x. So opening the angle out may in fact reduce the load placed on the point that the rope runs over the PSP, but the direction of force may be leveraging the tree instead of trying to compress the wood.
There may be times when you feel the advantage of a remote anchor is suitable. That is the great thing about SRT...endless options.
Donny

 

[bonner1040]

Cupressus, whats you first name buddy?

The VTIO has a great document called "Working the Angles' which should answer some of your angle questions.

http://vtio.org.au/Content/wp-content/uploads/2010/07/Working-the-Angles-i.pdf

For me the core tool in my 'toolbag' is judgement. Like hardware has safety factors, MBS, and SWL so too does a TIP/PSP. You may not need to understand all the deflection, MA, and force issues fully but having a general Idea (2x, 4x,8x) of the effects you are putting on a rigging point/TIP/PSP is whats critical in avoiding failure. You may not be able to calculate the forces generated when negative blocking wood, but you know when to use a bull rope right?

Integrate a safety factor into your TIP/PSP selection and use your best judgement!

As fas as isolating, unless you are choking or setting certain retrievable methods why bother? A certain amount of isolation may be necessary to avoid being hung on really small stuff but basically you go with the best achievable scenario with the least bounce I guess..

When using a base tie its important to realize the potential to take a 2x whipper if a sucker or small branch fails. If the sucker/branch that is holding your line above a intended PSP/TIP fails, twice that distance of rope will be 'introduced' as slack into your system which could lead to quite the drop. 2 becomes just 4 but 6 quickly become 12!

Lastly while it doesnt compare to the efforts in the TCIA SRT Best Practices Manual there is an additional primer, also from VTIO that has god info. I think I have shared some of the VTIO resources with you before so if so I apologize for the redundancy. Here it is though regardless:

http://vtio.org.au/Content/wp-content/uploads/2010/07/Single-Rope-Technique-i.pdf

There are specific sections regarding line isolation and TIP/PSP selection.

 

[Colin]

Well said!

 

[oceans]

All of the references previously posted are great. I think that "vectors" could be explained (or understood) rather easily, and is good to understand before evaluating a PSP or Redirect any further.

Determine what the final rope angles will be once the system is loaded (standing side & working side) and bisect that angle. That will be the direction that your load will be applied to the branch. When you determine that, then you can go further in determining how much the load will be and whether or not the branch is suitable. This can become complex if you are routed through numerous redirects before ascent.

If you were to be climbing an "edge" tree (a tree at the edge of a tree line) with a heavy lean in one direction, it could be very beneficial to base tie to a tree well behind it. Once you load the line, you may actually be lifting the edge tree due to the vector.

Your understanding of deflection seems good. The wider the angle between the standing and working side of the line, the lower the force that is applied at that point.

Get yourself 'On Rope' and TCIA's 'Best Practices for SRT in Arboriculture' and dig in!

 

[Cupressus]

Excellent points all, guys!

I do understand vectors, and that was one of my earlier concerns even working SRT with a basal tie-in. 2x or something slightly less than that force applied at a vector halfway between where you are (simplification) and where the base is might make me nervous in a wide-spreading Deltoides cottonwood, whereas a DdRT system would have 1x the weight, but at a more extreme vector. All interesting and important stuff to contemplate.

I'm trying to get as well-informed as possible before I jump two-footed into the SRT world. I also have questions about tying into an excurrent tree with a downward-drooping habit (incense cedar around here) but first things first.

@Nick: I haven't checked out your link yet but it's next up in the queue!

@Oceans: Copy that, putting both books on the reading list!

And an excellent point about the edge effect! I hadn't thought of it that way but it's a great tool to use! Especially out here when I decide to go up some of these cool forest Black Oaks which all seem to be leaners

 

[Cupressus]

First name is Charlie, BTW

 

[bonner1040]

Charlie,

I think most tree workers say 60% couldnt spell vector or angle and that the remaining 30% in addition to the initial 60% couldnt understand how it impacts their daily work effort.

Of that, the remaining 10% might care but lack the understanding, you and others here and other places represent what is likely less than 5% of all of the people that 'do what we do'.

Nick.

 

[Adam_P]

[ QUOTE ]
I also have questions about tying into an excurrent tree with a downward-drooping habit (incense cedar around here) but first things first.


[/ QUOTE ]

Choke if you can. As long as it's not drooping like \ obviously. That's probably my least favorite form to climb.

 

[Richard Mumford-yoyoman]

[ QUOTE ]
Hey all,
........Are guys spending some time isolating for SRT as well?
In other words, does a wide-angle of tie in mean the PSP is supporting a fraction of the climber's usual doubled-weight?


[/ QUOTE ]
Hello Charlie,
I'm new to all of this and enjoying the learning, have a couple of thoughts to confirm and an example I will try to post a picture.
Seems every situation is different, I have a lounge chair hanging in a tree about 35' up, it is about 25' feet from the trunk, I have it triple crotched and anchored to a nearby tree, about 30' away and on the opposite side of the chair. Would it be fair to say that in this situation it would actually provide balance to the tree as opposed to anchored at the base? As the line runs across each crotch, the branch pretty much divides the angle, so almost all loads are compression loads.
Nick makes a good point I see about the drop if you have a base anchor or in this case even the canopy anchor and the PSP goes away. I had an experience close to the one I am putting in the photo.

Richard

Attached photo is a canopy anchor high in the tree difficult to see.

 

[Richard Mumford-yoyoman]

Next photo............2x the drop. 2'6"..5' How much of a load would that put on the branch?

 

[Cupressus]

Richard,

I guess I don't understand the question. Are you asking about load on the bigger branch in photo 2 in the event that the smaller branch breaks? In that case you're talking about a dynamic load, and that's tough to figure except to say it's gonna be a LOT due to the velocity of the load at the time of impact. If we're talking about sharing load of the chair between the two pictured anchors, i think I'd run the rope around the trunk over a substantial-ish branch so the load is directed downward towards the trunk rather than away.

And if we're evaluating the pics as examples of PSPs, they look like retrievables, right? In that case, it's an initial load of 1x on the PSP, which helps that little branch's situation, but in photo 2, if the little one does go, you do indeed drop 2 times the distance, and that makes the FORCE of impact pretty high. I couldn't give you an equation, but to give an idea, the SPRAT guidelines specify you can't fall further than 18" because beyond that you're at risk of some pretty serious internal damage... So a lot of force at 5' then. More than enough to sever your rope with your toothed ascender, at least - which is why I'm looking for reliable ways to set up breakaway footloops for my ascender...

I don't know if that just makes things clear as mud? Did I understand you at some point in there or is all this just babble?

C

 

[bonner1040]

In most cases when taking a dynamic whipper it isnt the load on the branch or PSP/TIP you are 'falling' onto that you should be concerned with, its the load thats transferred to your body through the semi-static arb rope you are using.

As far as the example pictured, when that sucker breaks likely you just get a jolt, not much more. If you are running a saw though when it happens??

Question though, thats just a choked anchor right? not a base tie? If so, there is still roughly 2x on the sucker, but if it breaks after whatever dynamic load hits the larger PSP/TIP then it will just be 1x. Assuming though thats a live branch it would take a hell of a lot to break it at the union like that.

 

[Richard Mumford-yoyoman]

[ QUOTE ]
.....
I guess I don't understand the question.
C

[/ QUOTE ]

Sorry Charlie, I did ask too many questions at one time and made it confusing. Let me just address the base anchor now, have to run but when I get back I will ask about the in tree anchor.

I had a 3 year old make a drawing for me.
In this case I would choose 1 then 3 and last 2.
For me, the question of where to make a base anchor depends on the situation. As Oceans points out, on an edge tree, the anchor may not be best at the base of the tree but an adjacent tree.
Does this sound right?

 

[Tom Dunlap]

Load the tree along it's natural compression/tension lines. Loading at off-angles puts twisting loads on the tree or PSP.

 

[Cupressus]

Nick,

Oh right, my bad. Didn't think example 2 through quite enough. The anchor in that case is the branch below, while the psp is the small branch above. Thus, 2x weight.

@yoyo: The drawing makes sense to me. Is there a real advantage in redirecting so many times other than making absolutely CERTAIN that the load is directed in a compressive direction?

I'm coming to the understanding here that vector is actually more important than load in SRT planning. Obviously while you're climbing it's a moving-target, and you should just have a better awareness of what multipliers you're working with at a given moment. I'd like to see a more complex force diagram of a climber on SRT moving through lots of redirects. maybe I'll go find a 3 year old to draw what I've got in mind as well...

C

 

[DSMc]

[ QUOTE ]
...Does this sound right?

[/ QUOTE ]

Yes, you have the right idea. Generally, if the rope enters and leaves the crotch at the same angles, the branch will be loaded in compression.

What you need to watch is the changes in angles that occur once the line is loaded. These changes can be dramatic when working the outer canopy of tall or whippy trees. Your first clue, other than visual, will be a very soft or bouncy feel to the climbing line. Besides the strength loss, once you reach the first crotch, and unload it, it will try to suck you and your line over the top of it.

Dave

 

[Richard Mumford-yoyoman]

[ QUOTE ]
.... The drawing makes sense to me. Is there a real advantage in redirecting so many times other than making absolutely CERTAIN that the load is directed in a compressive direction?

I'm coming to the understanding here that vector is actually more important than load in SRT planning.

C

[/ QUOTE ]

Some great points I am reading. In my mind the vector makes the load and changes with every move.
In my mind EVERY situation is so different that I try to figure each in a separate way and be flexible enough to use each to best advantage.

To my photo..
One of my first considerations in setting an anchor is I would rather have my 200 pounds on it rather than 400....then I go from there.

One day I set an anchor in the tree, sent up my butterfly, looked good from the ground, got there and realized I had cinched two branches, thought, no biggie, it should be stronger that way, thought some more.....not so fast Sherlock, the branch below was actually getting lifted up, the branch above, pulled down like a base anchor, my 200 became 400 on the branch above, then the what if? .......what if it was a small branch like the picture, and now the point also made that 2 or 3 feet becomes 4 and 6 for the drop if the little branch breaks.
Tell me if I am making sense.....so much to learn and so much to figure.........loving it all.

Be careful getting work out of a three year old, they cry really easy.

 

[bonner1040]

http://vtio.org.au/Content/wp-content/uploads/2010/07/Working-the-Angles-i.pdf

http://vtio.org.au/Content/wp-content/uploads/2010/07/Single-Rope-Technique-i.pdf

See the links above, the answers to your questions are in there!!

Since no one seems to click through here are some of the helpfull pictures contained in there. To read the explanations and analysis you will have to check the documents as I cant republish it in its entirety here.

Jeezlaweez