Basejumper.com - archive

Maybe this is just my over active imagination, but why are cwy's not set up with snap shackles? It seems to me that would be very convenient and time-saving.
I have an extra and was considering making one this way. The only concern I would have for the setup is its load bearing capabilities.
Does anyone know what a standard RSL snap shackle's load bearing capacity is? If it's high enough, I'm putting a double finger trapped loop of dacron on one and calling it a win. Just quick link the two break cord strips to the bridle and then at the object you just pop the snap shackle closed on the bridle with the cwy around your anchor.
Sounds like it would work anyway...

Load bearing capability and expense. The snap shackles cost a lot more and are quite strong.

Check out the $1 key chain carabiners that Home Depot has up by the registers as of this fall. They're rated to 160 pounds and are very fast, but they are a bit bigger than a screw link. I'm not sure if I'm happy with them in this application, but I will continue playing with them.

Sounds like it would work. I think the key on all this CWY stuff is the question of how quickly you need to get off an object. Ive jumped alarmed door buildings, and been able to tie off with my CWY which doesnt have any additional attachments, in about 30 seconds. I only use one piece of break cord for all my jumps though.

Why?

I'm honestly curious. It obviously doesn't take any more time to set a backup piece on the carry on set up, and you're obviously a thinking jumper, so I'm interested in your reasoning.


FWIW, the simplest set up I've seen is one that Avery showed me probably 10 years ago. It's hard on bridles, but he just tied two knots in the bridle and connected the with break cord.

I prefer Lowes.

You can get them for 8 bucks or so on milspecmonkey.com

I have a handful of different CWY static lines that I have made for different obejcts which basically only vary in length. For each jump, I have the same length break cord pre-cut, so basically I do the exact same thing on every jump of going through my two cwy loops and then my bridle. I tie the cord very tight, and feel confident that basically the same exact forces are in place on the same exact system on every single jump. Its a very easy setup and Ive become very comfortable with it. I feel that the likelihood of premature breakage is very low on my tightened one cord system, so I feel ok with just the one piece of break cord. I dont think its wrong at all to use multiple, I just feel very comfortable in mine. In systems that require a longer loop, or have potential for abrasion or other factors, I think having a backup is totally reasonable. On almost all my static line jumps, I climb down or tie off so the bridle is closer to full extension as well, which I feel also lessens some of the dynamic forces of extraction. This being said, I inspect my piece of break cord before tying off every time, and always have two pieces in case I dont like the look of one of them.

I did some testing this summer of breakcords.

And my observation is that you should not rely on the "visible inspection" of a breakcord.
What I mean by that is even if the cord looks good, it can break prematurely.

Sometimes you can see the damage of the cord very easily, it's like the machine messed up for a couple of inches but there can be defects that you don't see.

I had one piece that broke at ~50-60 lbs (expected force was 160 lbs), and I could not see any defects in it before or after it broke.

Also about tieing the knot tight.
I did not make any tests or write anything down, but as I came to the end of my tests I started noticing a difference in tensilestrenght of the tight knots vs the lose knots.
And by tight knot I mean a knot where (in a CWY system) the dacron loops are "forced" together by the breakcord.
And a lose knot is what I would call a knot where the dacron loops and the breakcord can move.
As I wrote earlier, I did not make any tests of this, this is just what I started noticing after pulled apart about 60 breakcords in different systems.
But what I could see and almost predict is that the tight knots broke early by about 10% less pullforce needed.

But that is not in any way scientific, it's just what I "noticed".

One of the other things I would like to know is how much force is actually applied to need extract pins and a canopy to line stretch. I would guess no more than 20lbs given the PCAs ive done over the years.

I think the video that apex did with dropping a 5 or 10 lbs weight or whatever it was and showing the cord break is a dumb analog, because if you took an actual rig and threw it off on that same system, it would definitely extract the pins and canopy, otherwise I would be dead 100 times over already.

I think the tight vs loose knot is interesting and something I havent really thought of. I definitely tie a tight knot, and tie a series of 3 surgeons knots to lock it off.

I definitely think slack in the bridle is something to consider as well. As ive said, i like to climb down or tie up so i dont have a ton of slack in the bridle if possible, thereby hopefully reducing some of the dynamic force in play. I think its probably another one of those things where a lot of stuff works, as you really dont hear about people dying constantly from premature SL breakage

I actually used a spring scale and test dropped about 15 times off a little bridge (too low to actually jump) near Davis, maybe 12 years ago. The numbers averaged less than 20 pounds, if memory serves. I made a post about it somewhere waaaay back then, but most of my technical posts have been purged from the forum I used to post them on, and I don't have the data myself anymore.

Thanks tom, thats actually really interesting and helpful to know. Does anyone know if there is any type of loss of strength in break cord if you pretension it or "test" it and it doesnt break? I know differing materials gain or lose strength when they take a force through them. I cant imagine I can apply much more than 20 lbs to a cord, but when i tie off, i definitely pull down on the bridge until everything has tensioned and to make sure there is no slippage in my knot.

I'd be interested in testing a bunch of this stuff out.

I'm still trying to finish setting up in the new school building, but once I get through that maybe I'll try to do some tests on video and see what I can come up with.

My intention was no at all to say your setup is dangerous, only that you should not trust breakcord at face value.

We have all seen the video of the premature when someone jumped a bridge, and I would be surprised if the jumper saw a defect in the cord and still used it.

So basicly what I'm saying is, sometimes there are defects that you might not see and they can still be dangerous.

I also do one surgeonsknot and at least three square knots or however many I can do on the piece of cord I have.


What I also found out is that the cord does not break at the knot.
And that the CWY-part of the "frictionfree" system does not slip out of the 900 lbs dacron if you make a bartack with E-thread.
The bartack was tougher than my Spectraline I use for CWY-part.

No, I think this is a great discussion of all these points. My break cord almost always stays stuck to the bridle when I land, and about 95% of the time, its broken right in the middle into a perfect X with the knot still intact. I have had a couple of times where the cord breaks right next to the knot so I get more of a y shape.