SL jumping

[rfarris 1]

For those of you who make S/L jumps, what exactly are you using for the line? What exactly is "brake cord"? How are you attaching it to the PC, and/or canopy, and how much line between the attachment and the tie off?

Okay, 200' object, freestanding, nice landing area. I've read how some experienced jumpers would freefall this object, handheld, and some would even go stowed. (I've seen the nice Xray photos in the Accidents category over on BLINC) What are the advantages of going SL, PCA, vs freefall, besides the obvious quicker canopy extraction.

thanks

Rod

[base704 0]

(insert favorite pre-post disclaimer here)

I personally use 80lb break cord, tied to a piece of dacron suspension line, which in turn i usually lark's head to the object. I connect the bridle to the break cord with a rapide(sp?)link(canopy connector link)at the p/c end.
The break cord is what it sounds like: a cord designed to break at a pre-determined point. In this case, 80lbs. Most of the manufacturers sell it.

As far as the 200 footer goes: I'd s/l it.
But, then again, I'm a big wuss.

You can get a lot more done with a kind word and a gun than with a kind word alone.

[Basejumperjeff 0]

I'm the same as 704, I use 80lbs. break cord. I do rig a little differently thought. I use a peice of 13mm - 15mm climbing rope tied in a loop then looped around a hard point at the exit, tie my break cord thru the bridle, leaving the pilot chute on, and around the climbing rope with a surgeons knot.
I have done 200' both s/l and pca, with a proper pca from someone you trust, I prefer the pca. Don't know why just feels better.
Although you can freefall 200', I don't think that I would have the balls, but we have talked about it at the exit point, just none of us have ever tried it. I have freefallen 260' and that was scary enough.

[SkyMissy 0]

Okay, I'm pretty sure I'm getting the right picture, but can anyone post a drawing of your favorite setup? Do both of you actually loop the break cord?

________________________________________________
Mike

[Faber 0]

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I personally use 80lb break cord, tied to a piece of dacron suspension line, which in turn i usually lark's head to the object. I connect the bridle to the break cord with a rapide(sp?)link(canopy connector link)at the p/c end.

Same here.Thanks BASE 700

Stay safe
Stefan Faber

[blair700 0]

Yo!!

Hopefully 704 will post a pic, I know he's at home now doing nothing...with a new camera, and slick computer....but like he said, he's a wus so I'll do it tonight if he hasn't by then.
Faber, no problem at all, I used some yesterday off a 240' span, had a nice opening and a very fast, but soft landing. I'll try to send you a compressed vid of it later. Hope all is well for you.
Also, I'd rather do a S/L than a PCA, cause all my friends think its 'cool' to throw your PC past you right after the ya, in C-ya. They call it freefall assist
Later
Blair

[Faber 0]

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I'll try to send you a compressed vid of it later. Hope all is well for you.

As long as its under 10mb you can send it to my mail,or else try to use your msnAll is fine here

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I'd rather do a S/L than a PCA, cause all my friends think its 'cool' to throw your PC past you right after the ya, in C-ya. They call it freefall assist

Why aint i suprised

Edit:by the way i manneged to save that poster,you should have seen my insurance guy as he payed me a visit(new insurance that cover BASE)

Stay safe
Stefan Faber

[base704 0]

see if this helps...

the second pic is the s/l larksheaded to a barstool...

700...nice job with the IFR jump up north!
i'm really sorry that i couldn't make it...
let's get back to tearin' up the local scene, eh?
we could always start in your back yard!

DWAI!

You can get a lot more done with a kind word and a gun than with a kind word alone.

[rfarris 1]

Thanks 704 That's what I was having problems seeing, I understood the explanations, just couldn't get the picture, but it's clearer now.

One question though: Does it matter what type of barstool you use, I mean, probably don't want one too heavy, with the climb and all.

Rod

[base704 0]

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One question though: Does it matter what type of barstool you use, I mean, probably don't want one too heavy, with the climb and all.

Ahhh...When faced with this dilemma one is dealing with the proverbial double edged sword...
Too heavy a bar stool, and the climb becomes brutal.
Too light a stool, and you run the risk of bringin' it back down with ya and a total.

'Tis definitely a very personal choice...

You can get a lot more done with a kind word and a gun than with a kind word alone.

[SkyMissy 0]

Thanks guys!!

________________________________________________
Mike

[fundgh 0]

In the picture, the break cord is looped...does this not increase the force required to break away...

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Do both of you actually loop the break cord?

Looping the cord would give you twice the force required to break away since it is divided by two pieces of break cord.

...FUN FOR ALL!

[hookitt 0]

It's still one piece of Break cord when using a loop. It will break in one spot therefore minimizing any added breaking force. It will not double the amount of force required to break it.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[rfarris 1]

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It's still one piece of Break cord when using a loop. It will break in one spot therefore minimizing any added breaking force. It will not double the amount of force required to break it.

So the cord will most likely break at the point where it is looped through the peice of suspension line in this example, right? Therefore leaving the remaing cord that is larksheaded to the structure?

Would it be just the same to have the single loop attached at the structure and the larkshead on the supsension line so as not to leave trash behind?

Thanks
Rod

[TomAiello 25]

If the piece of the structure you attach to has a sharp edge, you may find the cord breaking prematurely (essentially being "cut" by the corner of the attachment piece).

I always use something else to tie to the structure. If it's a rounded bar, you should be able to get away with tying the cord to it, but if it's square, be careful of premature breakage.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[fundgh 0]

I see what you are saying, but my physics studies tell me differenly. If the force was applied directly toward and away from the PC and the larks head, you would be pulling on two pieces of break cord. I know that practical experience is worth a lot more than theoretical calculation in these situations, I was just trying to calculate the whole thing out (nerd style!)

...FUN FOR ALL!

[base689 0]

> So the cord will most likely break at the point where it is looped through the peice of suspension line in this example, right?
Not exactly. The break cord tends to break very close to the knot (=the weakest part of the whole "system", granted that you avoid sharp bends around sharp corners), that's why we do the surgeons knot onto the break cord: such a knot minimizes the "sharp bends" on the cord, letting the system to have a break load very very close to the break load of the "perfect" (=without knots) cord.

> Therefore leaving the remaing cord that is larksheaded to the structure?
Normally, you end up with leaving ALWAYS some piece of static line (=non-breaking rope) attached to the structure. Sometimes, the (broken) break cord remains into the loop of bridle, sometimes the (broken) break cord remains into the loop of the static line, that is fixed onto the structure of the object.

> Would it be just the same to have the single loop attached at the structure and the larkshead on the supsension line so as not to leave trash behind?
It is NOT such a huge pollution to leave behind few pieces of ropes behind.
Listen to what Tom said: it is NOT wise to tie the break cord directly onto the (metallic) structure. It is much better ALWAYS to tie the static line onto the structure, so having such a static line to "absorb" any unevennes of surface/structure, allowing the break cord to break exactly in the same way/situation/load on ALL your jumps.
Furthermore, using the system break cord+static line you have a double advantage:
1) you use a very small amount of break cord per jump (I use 10" - 25 cm of break cord on each of my SL jumps)
2) as static line, granted that you are going to lose it, you can use a cheap line/rope, provided that you do a double/triple/quadruple loop onto the structure; personally, I use a 1/6" - 4 mm rope (used in boating) and I do a triple loop onto the structure.
Plus, it is a very nice and "fast" set up: I prepare at home the break cord loop passing through the loop in the bridle (actually, I use a special bridle made up of a dyneema 5.5 mm - 1800 kg climbing rope, but this is another story), I pass through this break cord loop about 1 m of the above 1/6" - 4 mm rope, I leave it there and I pack all this nice stuff into the PC and I put this set up into the BOC as if it were "going stowed".
Then I climb onto the object, I approach the exit, I don the rig. At this stage, I pull all the stuff out of the BOC, and I usually do a triple loop with the 1/6" - 4 mm rope onto the structure, passing also ( Just my 0.02€.

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[base689 0]

> If the force was applied directly toward and away from the PC and the larks head, you would be pulling on two pieces of break cord.
You are absolutely right on, chap!!!
The "80 lb - 36 kg" rated break cord is rated so by BASE gear manufacturers because you are meant to use it closed in a loop (and then closing the two ends with a surgeon knot). Such a "system" breaks at 80 lb - 36 kg.
Now, it is quite obvious that when with the bridle you are pulling and you are approaching the 80 lb - 36 kg, actually you are exerting a force of 40 lb - 18 kg per each of the two "branches" of the break cord forming the loop: whichever of the two "branches" is slightly weaker than the other, it will break there.
The break cord we use is a 80 lb - 36 kg break cord granted we use it in a loop fashion (each of the two "branches" takes half on the load), but the break cord in itself is a 40 lb - 18 kg break cord.
If you consider the following set up: fasten a loop with a knot around the structure, then coming off this knot there is the break cord pure and simple (= a single line of break cord) for few (or many, it's the same!) inches/cm's, then fasten the other end with a loop and a knot around bridle loop: such a system is going to break at 40 lb - 18 kg, be sure about that!!!!!!!!
There must be a reason why, as static line, I use cheap (boating) 1/6" - 4 mm rope and I do a triple loop around the objetc structure: 1 loop = half load onto the rope itself, 3 loops = 1/6 of load along any of the 6 branches of rope.

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[DexterBase 0]

I had an idea for a system that wouldn't leave anything behind at the anchor point.

I thought of the snag possibilities when the sling whips around, but as long as there aren't any huge burrs on the beam or rail, it should be okay.

The spectra is very strong so I'm confident the system will give exactly where it's supposed to.

Let me know if you see any problems with it.

P.S. If my highschool drafting teacher saw this he'd kick my ass.

[Faber 0]

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Let me know if you see any problems with it.

You forgot your pilotchute dont SL whith out... or else i think its a super system,i think ill make one myself(if theres no other coments than the pc)..

Stay safe
Stefan Faber

[bps 0]

Hello --

Not that this system wouldn't work, but one thought comes to mind at first glance. It seems to me that this system would require a greater force to actually break the 80lb break cord.

Looking at the picture, when force is applied to the system, the load will have to travel up through the climbing sling and over the railing and then onto the break cord itself. Essentially, you're introducing a pulley effect with this system, resulting in a higher force in order for the break cord to snap. As to how much force this is, I don't know. But it could be enough to lead to center-cell stripping, etc...

Thoughts?

Bryan

[rfarris 1]

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I had an idea for a system that wouldn't leave anything behind at the anchor point.

This was my point from a few posts up. I'm not all to concerned about littering, just wondering how to rig a SL with out leaving evidence behind. Some are concerened about those things.

But like bps, my very first impression of your system was whether the break cord would actually break when it needed to. I guess my uneducated reasoning saw the thicker rope taking most of the load, and eventually transferring it to the smaller cord.
I've never done a SL jump, hence the reason for this thread, so I could be wrong.

Rod

[DexterBase 0]

My logic is that since spectra slings don't stretch at all, the load will be transferred to the breakcord.

The pilot chute was left off the illustration for simplicity. I had hard enough time drawing a passable rapide, can you imagine if I'd tried to draw a pilot chute???

I wonder if we could recruit a physics wizard to explain exactly how this setup would transfer load to the breakcord.

Edit: After more thinking about this, it seems to me that the pulley effect is not an issue. If one end of the breakcord was anchored to the bridge after running aroung a handrail or beam, then I could see how the friction from the "pulley" point could be an issue. The way I set it up, the breakcord will start loading the instant weight is applied.

It seems to me that since both ends of the static line sling are attached to the same loadpoint, that both sides must share equal amounts of the force. Since the breakcord will part at 80 pounds, as soon as the system is loaded to that point, the breakcord will give. It's a weak link designed into the system.

[base689 0]

Bps:
> …It seems to me that this system would require a greater force to actually break the 80lb break cord…
> …As to how much force this is, I don't know…
Simply, twice as much force than the “traditional” set up of break cord.

Rfarris:
> I guess my uneducated reasoning saw the thicker rope taking most of the load, and eventually transferring it to the smaller cord.
No. it is NOT a matter of how thick is any rope/cord. It is a matter of how many “branches” there are to bear the load. Quite simple. 1 branch (=1 single line of rope/cord/whatever): full load; 1 loop (=2 branches): ½ load; 2 loops: ¼ load on each branch and so on. Then, in case of 1 loop, each branch takes ½ load: the system breaks where the one of the 2 branches is weaker (=the one that has got lower break load) than the other.

Dexter:
> My logic is that since spectra slings don't stretch at all, the load will be transferred to the breakcord.
Yes, the spectra sling streches very little (no system/no rope has got infinite rigidity), but that is NOT the point. The point is, as I said before, that the full load (=the force transmitted by the bridle) is divided by as many times as the number of branches of the system.

> It seems to me that since both ends of the static line sling are attached to the same loadpoint, that both sides must share equal amounts of the force.
Yes, this is true.

> Since the breakcord will part at 80 pounds, as soon as the system is loaded to that point, the breakcord will give. It's a weak link designed into the system.

Not at all. Yes, the loop of break cord will part at 80 lb - 36 kg, but to get to 80 lb - 36 kg on the loop of break cord, you must pull the bridle with a 160 lb - 72 kg force.
Can you see the scenario? You have a pulling force on the bridle of 160 lb - 72 kg (you are about to break the system): this force is transmitted entirely on the rapid link. Then, the force of 160 lb - 72 kg is divided by two simply because there are two branches after the rapid link towards the fixed point onto the structure: two branches forming the sling loop. Each branch of the sling takes (=must take, forces can neither disappear nor increase, they can only be distributed/shared among various parts of a static system) half of the load: so each of the branches of sling takes 80 lb - 36 kg. Now, there is one branch of the sling that contains the loop of break cord: yes, it is going to part, but at this stage you are exerting, through your body, harness, lines, canopy, bridle a force of 160 lb - 72 kg, that is exactly the double of the force at which the system is supposed to be loaded and break.
Be careful: in a static system where there are forces that are exerted along a pillar/rope/line/whatever, any time along such a system is inserted a “loop”, each branch of the loop takes half the load (the total force transmitted can neither vanish nor increase).
Remember that with a suitable system of pulleys/ropes/turns of the rope along/around the pulleys, if you anchor such a system on a high point that takes all the load (=weight), exerting with your hands/arms a small force you can easily pull up a very heavy load: a grand piano, a safe, a car, whatever. The more load/weight you want to lift, the more pulleys and the more passes of rope through/around the pulleys need to be done.

Now, to take the good in your system, Dexter, you should simply use the break cord in the following way: you do one loop with a knot around the rapid link, then, off this loop/knot must come out only one single line of break cord (=the break cord pure and simple), then this single line of break cord “travels” all alone towards the loop in the sling: here you fix it with another loop/knot. This system is going to break when a force of 80 lb - 36 kg is exerted by the bridle onto the system.

Just after I wrote the above, I am wondering why you are use the rapid link, a component that is unnecessary (and that could fail…), at this stage. Has the sling got two (small) loops? You fix one end of sling with a larks head knot onto the bridle loop, then you fix the other end again onto the bridle loop using the break cord with a SINGLE LINE OF BREAK CORD (loop/knot, single line of break cord, loop/knot). Furthermore, the rapid link creates a sharp bend for the break cord: this way it could break at a load lower than the load it is supposed to break. We use static lines onto the structure to avoid sharp bends/sharp point of metallic structure to make the break cord properly, and then you introduce a very sharp bend through the rapid link (even if smooth surface, but still is very sharp bend (=small curvature radius))?!?!?!?
Just my 0.02€.

Stay safe out there
Blue Skies and Soft Walls
BASE #689 - base_689AT_NO_123_SPAMyahoo.com

[DexterBase 0]

That was exactly the explanation I was looking for. Thank you for taking the time to write that.

I also spent a few hours researching various pulley systems and mechanical advantage and came to all the same conclusions. I stand corrected.

I am still going to do pull tests and see how much I can vary the breaking strengths. I do know that you can greatly vary the distributed load (and thereby changing the breaking point) by changing the angle of the sling.

As far as why I used the rapide, that's a good question. A girth hitch (larkshead) is a better choice. I guess it stems from my climbing background where nylon rubbing on nylon is bad. In this situation where friction is a minimal concern, the larkshead is the way to go.

Back to the drawing board....