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This is a technical discussion of why "the bridle ripped clean off" from this post First BASE jump .
so please keep it that way for those of us who wish to learn.
So why did the bridle rip clean off?
take care,
space
#64 - Muff

user error?

I have video of a bridle being cut in half on a static line jump, after the canopy reached line stretch. In that case, my best guess was that the bridle had somehow blown up and around one of the bolts holding the structure together. Unfortunately, no retrieval of the remaining part of the bridle was made, so I don't think anyone can say for certain.

However, in the case you are referencing the question is different, because that one was a PCA. I'm not clear on how the bridle, which ought to have been managed by the PC holder, could have gotten loose and wrapped around something. Totally wild guesses might include poor PCA technique (premature release of the bridle/PC) or poor placement of the PC holder (so that the bridle was dragged over a sharp edge before line stretch pulled it tight).

By the way he was talking it doesn't sound as if his knowledge of gear is all that high. I wonder if he was referring to the shrivel flap the entire time. Unless he was doing a SL; and we know this was not the case, nothing should have ripped. It sounds like you all know the history of the rig in question. Is it an actual BASE container or a pseudo hunk of crap? Anyway, it sounds to me the entire problem is that he's not familiar with his/whoever's gear.

I am wondering also Tom. I know that there is a technical lesson here that we all could benefit from. I've never heard of this situation happening before and as a rigger/BASE jumper, I would like to know. I just hope he tells us.
I've seen a lot. I've learned a lot and am still learning.
take care,
space

Tom, can you please post the video so that we can all learn from this potentially fatal situation?

Thanks!

I believe that the jumper already posted it on Skydivingmovies.com. Let me see if I can find it, or maybe he'll read this and post it for us.

The only way I could see something like this being really bad is if the bridle didn't tear, and the jumper was left hanging from the object.

I'll try to dig out the video and throw it up there.

Thanks!

It would happen at line stretch and loading and so not much of a physical risk more than normal. Things would have to be extraordinary for it to break before the canopy is fully extracted. I have seen something similar (extraordinary) where the rocket of a deployment system accelerated in the beginning to open the container but overloaded the attachment point of the canopy midway through extraction phase.
take care,
space

How hard is it for Andy to chime in and say yes or no to these questions?

Maybe potatohead's grip was so strong, line stretch and loading wasn't enough to pull the bridal out of his hand and it broke after 400lbs of pressure?

from the sounds of it, it was bridle breaking... not ripping out from the center cell.


the only thing I can chime in towards this conversation is that the container was "a dolphin container modified for BASE and a fury 220"

Could the d-link have come undone?

I really hate all this speculation...

It was a question (Hint) -->> "?"

<<from the sounds of it, it was bridle breaking.>> - sure looks like speculation too

To be fair, Andrew did have a PM from Andy, so he might have more information that was relevant when he formed that opinion.

I guess that my hyper sensitivity is taking over from the mind reading... A question can be invalidated by information (whic I didn't have) but it was far from speculation, in my way of thinking..... I'll get my coat.

I'm currently uploading two copies, called "Static Line Bridle Tear" and "Static Line Bridle Tear Full."

1) Just the jump, shot from the ground, encoded with DivX and about 1 MB. About 20 seconds.

2) The ground footage, plus the POV footage from the jumper, which includes footage the entire time he rigs the static line attachment. It's kind of hard to make out due to camera angles, but maybe you can see something there about how he set it up. Quicktime, about 60 MB, around 9 and a half minutes.


If someone sees that the uploads have been approved and posted, can you post here and let people know?

If it did, that would open up a whole different question of why a D link was used. Normally, BASE bridles are just girth hitched into either a metal ring sewn to the canopy, or fabric-on-fabric to the bridle attachment point. With that setup, though (Fury in a converted Dolphin, which sounds like the "Death Rig"), there's no telling.

Thanks you.

I was speculation too... it was a statement towards the entire thread (myself included) not just you.

Sorry, I apologise for going off on one. - my bad .

A little birdy told me.

Its up..
http://www.skydivingmovies.com/...ion=file&id=5692

What are your thoughts to the following in the Clip..?

It looked like the excess bridal was 'held' or even left ,rather than S-folded and held in place by a loose bungee stow...could that have contributed to it wrapping around one of the many snag hazards there....(I've not seen the jumper holding the excess bridal on a S/L jump yet)

and probably not related the the PC breaking at all..just another observation...
The back up static line didnt seem to have any more length/redundancy than the primary static line.....
Doesnt having two S/Ls the same length effectively double the overal S/L breaking strength ( 160lbs if it was standard breakcord)?

Just observations, not criticism...I think maybe alot can be learned by looking at these types of incidents in detail...

two things I noticed... like you said, the bridle/PC was just grabbed and held in an un-organized manner...


secondly... look at this screen capture (attached)

it looked a bit (cross)windy at exit, the pilot chute is completely inflated and moving to the side.

Been there, Done that.

so how did you get out of that situation?

what any skydiver would do. he cut away.

I had some help with that though.

If you're hanging from the tower structure itself, and relatively uninjured, it's possible to climb back inside and onto the ladder. Otherwise, you're stuck waiting for rescue (either from other jumpers on the load, or more formal rescue from emergency response personnel).

but only if he could get good hold of the object, so he wouldn't fall down? i was just wondering what to do if he didn't find anything on the object to grab. but that's probably not a concern on antennas?

bounce up and down in the harness until you break loose!!!!! now THAT would be a cool unpacked jump.

Wait for rescue. Either (hopefully) your friends who brought rescue gear to the jump (because we all do that--right?), or guys with flashing lights and helicopters.

thanks man. i realy LOL. who the fuck is useing that acronym? thats fucked up.

it must be an enormous shock to fall and then be appruptly stopped by the bridle? i mean physically...

I'm not aware of any cases of this happening on a BASE jump, but I agree that it would be a tremendous physical shock. I do know of some cases where a similar thing happened on static line jumps from aircraft, but in those cases the jumper would have travelled less distance before stopping (because they were closed container incidents).

it sounded like stitch experienced hanging after the bridle from an object? wonder if he experienced the extreme physical shock.

well, lets look at it.

bridal max length is 9'
canopy to lines is what? 3'? 4'?
lines are about lets say 17'

we are talking 30' almost here.

speed would be about um, math. i love math.

however, dacron stretches, not a lot, but enough. the tape used in canopies streteches, as well as f111, also not a lot, but enough. the Webbing used in bridals is really not that strong, and it stretches a LOT when loaded to what we are talking about.

it would be like this kid,http://www.fugly.com/...394/bungee23432.html

he is some serious competition to our rope jumping systems, obviously.

but seriously,

I would guess that a 3.5sec vented slider down opening would be comparable to this.

also, I would doubt, seriously, that a bridal would take it.

those bridals are not terribly strong. and to be caught by a bridal would mean your being hung byt only 4 suspension lines on your canopy. A 30' fall can produce some SERIOUS forces. I would know.

I do not believe so.

If memory serves, Stitch hung from a tower in a more typical BASE fashion (following an off heading opening and object strike).

That would be correct.

It would double, however it would not be 160lbs. 80lb breakcord looped once will break at 160lbs, best case scenario (no uneven loading on the sides, etc - which is hard to do with the way we tie static lines). Since knots weaken the strength, it's lower. A surgeon's knot weakens it around 40%, which is pretty good. So you end up with 96lb breaking force max with a standard piece of 80lb breakcord tied with a surgeons knot. (80*2)(1-0.40)=96.

So the force in that situation would be 192lb, not 160.

Could you explain that some more..?
Woudlnt a piece of 80Lb breakcord break at its weakest point....where it is single strand and not where it has been knotted and looped aroudn itself for the knot.
On the limited number of S/L's I have done where I can observe the breakcord post jump.. the shear point has never been at the knot...but on the portion looped around the anchor point

Thanks

the weakest point is the knot.. since it loses 40% of it strength at that point.

all the ones I've seen break next to the knot...

I'll try and get a pretty little chart out of poynters, that might add well to this conversation.

[Poynters Vol.2 - pg347 - 8.80]

You're right about the knots... but that assumes that nothing is rubbing against any other part of the break cord.

Quite typically, the cord is tied around something that is relatively abrasive (a slightly rusty iron railing for example), which also fits with Zoter's experience (as also mine)

Actually my S/L experience has mostly been using breakcord tied on a flat climbing sling.
Please dont quote on my 'experience' when you have no knowledge of it....ta

I'm intrigued then how my breakcord is shearing usually about 2cm from the knot....consistantly
I'll get some pics the next time I can

See attached pic. Since the loading on the break cord is at a single point, which pulls the break cord taught, the load is spread evenly on both sides of the static line. In this case, T2 and T3 are equal, and breakcord breaks when T2=80lbs. Thereforce, since T1=2T2, the load will break the cord at 2*80= 160lbs. This is the theoretical maximum breaking force on the break cord. Since things such at tie off points and knots weaken it, it will never break this high if rigged properly. In the dozens of static lines I've done and seen, when tieing off to a fabric tie-off, the break cord always breaks at the knot. If it breaks elsewhere, then it means that something caused the cord to break at less than 96lbs of tension (approx).

Thanks
I think I'll take advice on how I'm tieing off the breakcord ....as its not the tie off point thats the issue I think..

getting back to my original reply...what are your thoughts on having a primary and secondary breakcord tie...that dont vary in length/redundancy...?

> I've never heard of this situation happening before and as a rigger/BASE jumper, I would like to know
——————————————————————————————
It happened to me nearly that incident. About this time in 2005. I took my student to our S we use for first timers (also for fun for us ); after all the training, preparation, exit trials, it came the moment for his first BASE jump.
I decided his first BASE had to happen via PCA, so we did.
My student sat calmly (...well...) on the handrail, which highest round horizontal bar is 2"-5 cm diameter, you sit on this, plus there other two round horizontal bars underneath, each of these two are 1"-2.5 cm diameter. His ass/thighs onto upper big bar, with feet on lowest small bar.
Handrail is all gray painted, nice smooth surface.
I had gloves on. I had my right thigh pressed against handrail, with a well balkanced stance.
In my right hand I had the S folded bridle and with two fingers of left hand I was holding the PC.
Vertical of my right hand was OUT of handrail, vertical of my left hand was slightly INSIDE of the handrail.
I intended to exert the pulling force with the S folded bridle in my right hand to open his containr and get line stretch, which I did, once line stretch happened, jumper with his weight simply pulled away the S folded bridle off my right hand, immediately followed by bridle pulling PC off my left hand.
In that split second I felt a strange ripping noise and a sort of hard opening. His jump went on uneventfully (apart form "that" event...) and landing was OK.
To make short a long story.
The pieces of handrail (big round horizontal bar and two small round horizontal bars) are 33 ft - 10 m long, each of them with "handles" sticked into concrete, being each single piece NOT welded together but simply "pressed" against the successive one, with a "broken washer" (with diameter slightly larger than bar itself) in the middle of the two.
My biggest fault NOT to check that exactly where I was standing there was a portion of big round horizontal bar containing one of such "broken washers", with sharp edge pointing up, protruding very slightly off the metal profile.
After line stretch and pulling the S folded bridle off my right hand, PC was pulled off and slided onto big round horizontal bar, with PC mesh getting caught on that protruding edge of broken washer.
Of course, mesh could NOT hold the weight of my student and ripped off, but that simulated a very high load break cord SL jump.
There was a 4" - 10 cm sort of round hole in the mesh. PC has been thrown away.
Lessons learned:
1) while doing PCA jumps, keep EVERYTHING (S folded bridle AND PC) OUTSIDE the vertical of structure
2) check for ANYTHING "not smooth" on the structure we are jumping off and take countermeasures in case exit cannot be performed away from such "uneveness".
As soon as I realized what happened, I got a very "cold shower". Glad jump went uneventfully (apart from my student feeling a very strong pull (and buy a new big PC )).
It was clearly my fault for not checking out every detail carefully; nonetheless, big lesson learned for my future students (also for situations in which I MUST do PCA to my experienced mates).
Hope this helps everyone to avoid THAT situation (bridle and/or PC caught onto structure).

warning: math below

Well, if they're both the same length then I wouldn't call the 2nd one "secondary" as both are acting in tandem. Obviously it's much better to have them varying in length in case something causes the first to break when loaded. The main advantage to different lengths is that if something such as a sharp railing cut the break cord prematurely, there's a chance it won't happen to the second one. If they're both the same length, you're trading off for a very small gain in overall breaking strength for no real benefits.

I think there might be some confusion of the physics of multiple break cords though. It would be nearly impossible for 2 pieces of break cord acting in tandem to do something like that. Also, when using redundant breakcord (different lengths), the jumper's momentum will be very similar, although a tiny bit more, after both pieces break when compared to 2 equal pieces.

Note that a bridle made from 1" squareweave has a tensile strength of 1000lbs, 1.5" squareweave is 1500lbs. I'm not sure how much the larkshead and stitching at the pc attachment point (which matters since the larkshead on that end is not loaded during a static line) will weaken the tensile strength, but I doubt it's anywhere over 60%. So my guestimate for the breaking strength of a bridle (which is low imo) is 400lbs. Canopies, as mentioned earlier, have a strength of more than 550lbs. It would take way more than 4 breakcords tied in tandem to cause something else to fail before the breakcord.

This should clear some things up:

Force (F) = ma
Momentum (p) = mv
a = dv/dt
Force = dp/dt (change in momentum with respect to time)

To get some concrete numbers to hopefully make this easier to understand, we'll assume that the jumper's center of mass falls 25 feet before reaching linestretch and beginning to load the static line in a significant manner. He weighs 160 lb (~5lbm - 5 pounds mass)
This means his velocity is 40 feet /sec.
His momentum is 200 ft * lbm / s

WIth 2 breakcords in tandem and in good working order, the breaking strength will be 192 lbf (pounds force, btw 32.2 lbf = 1 lbm). For this to *not* break, dp/dt < 192 lbf:

F = 192 lbf = dp/dt
dp/dt = d (200 ft * lbm / s) / dt = 192lbf
with some simple integration it shows that it would take nearly an entire second of constant momentum change before the static line would not break. So if the cord is loaded for less than 1 second if dp/dt is linear, it will break. I doubt there is any way the loading will be constant, so any spike over 192 lbf will break the cord. When you consider the speeds and distances involved, the breakcord is loaded for a very small amount of time. When discussing "shock force or load", people are mainly talking about the change in momentum with respect to time rather than static force.

In the case of 2 different length break cords, the overall change in momentum will be nearly equal to the previous example. The only reason it's different is due to the small, negligible extra inch or 2 of freefall the jumper gets between the two break cords.

In other words, if 2 break cords of equal lengths would cause someone a hangup, 2 different length of break cords should do the same thing, but the first cord will break and the second will hold the person. Using 2 different lengths of breakcord to try avoid a hangup is ineffective. (math below)

F1 = 96lbf F2=96lbf
dp/dt = d (200 ft * lbm / s) / dt
after breaking the 1st breakcord, dp/dt = d (200 ft * lbm / s) / dt - 96lbf
when loading the second cord, if dp/dt < 96lbf, the second cord won't break.
d (200 ft * lbm / s) / dt - 96lbf = 96lbf
d (200 ft * lbm / s) / dt = 192lbf
it's the same equation as for 2 pieces of static line the same length.

nerd

The purpose of using two different lengths of cord isn't to prevent a hangup, it's to prevent a premature breakage. It essentially gives the break cord, which usually works, a second chance in the event that it fails the first time.

The reason to make the two engage at different times is so that if there is some unusual circumstance that prematurely breaks the first cord, it is no longer taking place when the second one loads.

Without subjecting me to math, can you tell me if this line of reasoning is or isn't supported by your calculations?

and no, it isn't supported by the above calculations. It is, however, common sense.

May be I am wrong but from what I can see there is 2-3 inch difference between the first loop on the bridle and the second loop, which must mean the 1st loop tied the 1 nearest the pins is loaded first then the 2nd tied or PC end is loaded 2nd?
or am I way off?

surely 2-3 inch is enough difference between loadings on the SL?

Shouldn't you be repling to TJ?? He's the math geek.

You're right on both counts. As long as the first cord has enough room to stretch and break, the cords will be loaded separately.

Also, A PM I got made me realize I might not have been as clear as I could have. My main point was that there is absolutely no fundamental difference (neglecting an extra inch of freefall) between 2 break cords of equal length and 2 break cords of unequal length. The reason to use different length pieces is that it gives all the advantages of 2 equal length pieces along with a couple others. Any advantage to using 2 pieces of equal break cords is also an advantage to 2 different lengths, but not the other way around.

speaking of common sense, doesnt it seem right that if there is a mishap, and the 1st one breakes pre-maturly, that the same problem will probably cause the 2nd to break? even if its 8' up the bridal?

i know that 2 loaded seperatly would solve a SL rigging problem, but if you accidentaly have a wrap to break the first, can you clear it in 8' (.4sec)?

maybe the wrap-SL break would start the limb or body rotation to clear it, i dono. just thinking.

Keep in mind that the break cord has to overcome relatively little momentum to get the canopy out and to linestretch. It's very possible that whatever caused the first cord to break early will do the exact same thing to the second cord, but not break early because the first cord significantly reduced the momentum of the canopy.

dp/dt yo

Aye, agreed there, but in the case of something like a arm bridal wrap, i dono. and it could happen on a crowded A. or B. Or E. Or S. or O.

Pretty sure if you wrap on the static line you're fucked unless you get lucky.

I'm looking at you, twoply!

of course, if your doing a SL with no PC, just flail a lot and you will be fine. well. live through it kinda fine. maybe. flailing is good. i love sport where flailing is a technique.

that's a lot of math to prove something that's not correct

do some simple tests in the real world with measurements and you will find that:

- a single loop of 80lb break cord will break at almost 160lbs given a gradual and static loading, this is almost not affected at all by whatever kind of knot you use (it is really much harder to measure a dynamic load than a static load, unless you happen to have a load cell and data logger)

- two sufficiently different length loops of break cord will break at a load of around 160lbs each, whereas two loops with not enough length difference will generate a significantly higher load before breaking

arguing this point with fancy math only proves you do not understand the system sufficiently well to model it correctly with math, as a few simple real life tests will prove

'In theory, there is no difference between reality and theory. In reality, there is.'

cya

...
- a single loop of 80 lb break cord will break at about 0.6 · 160lbs = 96 lbs due to the 40% degradation factor caused by the knot for closing the loop.

Is that based on an actual experiment you've done with a tensile tester?

My own experiments have been in line with 980's. The cord broke between 150 and 160 lbs.

> Is that based on an actual experiment you've done with a tensile tester?
——————————————————————————————
No. Rather, it's based on Dan Poynter manual, which states that a knot onto a oline decreases its breaking load by 40%.
Indeed, it's very reasonable that a knot decreases the breaking load of a line: in fact, we use the surgeon knot to minimize the curvature.
Indeed, (nearly) every time tha a break cord breaks, it breaks AT the knot or very close to the knot.
The loop of a 80 lb break cord should break AT 160 lb if we could close the loop in a veru clean way (i.e., with several stitches in a row of seam along few inches).
I do believe that the tests you performed caused your loop to break at 150÷160 lb: this means that YOUR piece of break cord (single strand measured in a laboratory with special clamps) would have broken at 120 lb or so.
If it were a PURE 80 lb break cord, it's sort of strange that the know did NOT introduce any degradation in the breaking load.

F = dp/dt

all my tests show breakcord breaking at the knot when a 100lb weight is dropped from 3-4 inches. every time.

your real world tests do not accurately model a static line base jump.

breakcord's breaking strength is shock load, measured by dp/dt, not m*a.

suggesting that knots do not noticeably degrade tensile strength goes against decades of scientific and practical (rock climbing) knowledge. I'm pretty sure this knowledge will go back centuries/millenia as well, but I don't know for sure. to plausibly disagree with this precedent, you're going to need a lot of math and evidence

exactly how did you do your tests?


there is a very good reason labs and private companies spend hundreds of thousands of dollars on measuring equipment.

edit: I phrased "breakcord's breaking strength is shock load, measured by dp/dt, not m*A." wrong. technically it is measured by m*A. however, in this case, A is more easily described as dv/dt since A will not be constant, and is definitely not equal to gravity. A will be a vector going in the opposite direction of the load, which is usually in line with gravity's vector.

TJ, your entire arguent above can be summed up quite easily with the following equation:

Code

I'm fairly certain the properties of the break cord change when gradually loaded and stretched. This most likely explains why all force is not equal when applying it to break cords. It could be anything from the style of the cotton weave to the electromagnetic interaction of polymer chains at an atomic level. The latter seems like it could plausibly explain the reason why it breaks at 96lbs of shock force but can easily suspend more than that.

I think I'll ask one of my professors next week about it. He taught a class I took last semester which dealt with things like this.

Do you have any ideas?

poynter manual? we are base jumping home boy.

dude, break cord is cotton.

40%?
what knot?
every knot, in every kind of material, in every weave, in every angle, in different temperatures and saturation of knot. it all matters.

from 0% up tp 80%.

and yes, i have a dynometer/tensile tester, and yes. i have tested it.

cotton is in the lower margins of knot-weakening percentages.


while i have not tested 80lb break cord, i would say that it breaks closer to 140lbs than 80 when gradualy pulling/gradual load increased.

yeah, but what does that have to do with break cord relating to the base jumping environment?

edit: nm. forgot 689/m2c/sam were talking about loading it that way.

> poynter manual? we are base jumping home boy.
——————————————————————————————
Really? I am afraid we are mushroom packing our PC's according to what is stated (among another 1000 issues about parachutes, PC's e relevant equipment) on Dan Poynter's manual

> dude, break cord is cotton
——————————————————————————————
I perfectly know break cord is cotton, so what?!?!?!?

> 40%? what knot?
——————————————————————————————
Dude, don't try to break the hair into 10 pieces. We are BASE jumping, do you remember? Dan Poynter Manual says that a generic knot can decrease up to about 40% the break load of a line, that's why we do the surgeon knot (to minimize this decrease).
Yes, if you do a crap knot you can decrease break load up to 80%, as well as can be 0% if you sew two overlapping ends with a sewing machine; our responsability to do "proper knots" when closing break cord loop, as well as jolly impossible to have a sewing machine on exit point.

> and yes, I have a dynometer/tensile tester, and yes. i have tested it.
——————————————————————————————
It's a pity you didn't test it under REAL working conditions, i.e., a BASE jumper exerting his full weight about 10 m - 30 ft lower.
I do understands there has been lots of real tests but only with static weights applied.
In then end, in our great experience of SL jumps, it has never happend to any of us any premature failure of break cord, as well as we have never experienced an abnormal break load of such break cord (the 80 lb nominal break cord bought by ParaGear), doing the surgeon knot as a standard, also when using the break cord in the CWY device.

> while I have not tested 80 lb break cord, I would say that it breaks closer to 140 lbs than 80 when gradualy pulling/gradual load increased
——————————————————————————————
I could believe that, but I am afraid that is NOT the real condition of deployment of our break cord in a real BASE jump. We use it (=break it) applying istantaneously (...after the forces needed to open container and extract canopy...) our weight 10 m - 30 ft below; jolly difficult to test THAT real situation.

> My own experiments have been in line with 980's. The cord broke between 150 and 160 lbs
——————————————————————————————
Did you do your test under static load gradually applied to break cord loop? While THIS setup states indeed the break load under static load, it is NOT the break load under the dynamic conditions we apply onto break cord loop when we SL BASE jump.

That's awesome!

-Gardner

hmmm, my dynometer is pretty small. ill bring it on a jump sometime. but i never do SLs. your right though...

ill bring it to potato and jack some cord off a new kid and his super-BASE prep kit. that should solve the problem. ill even make it jump(the newbie)

on a different note, Cotton is about as in-consistant as it gets. even break cord varies a bit.


PSS-what is a surgeons knot? I do a figure-Eight. then a million little retard knots.

http://en.wikipedia.org/wiki/Surgeon's_knot

Aye, got it. thank you.

> hmmm, my dynometer is pretty small
——————————————————————————————
I do believe that to perform a test of break load under real dynamic conditions is jolly impossible.

> Cotton is about as in-consistant as it gets. even break cord varies a bit.
——————————————————————————————
Agreed. I knew that. So what? I hope that the nominal 80 lb break load value is an average (not to go below, possibly to go over). Being something used by military on military soecifications, I hope such a 80 lb value is "guaranteed".
We see the 80 lb break cord by ParaGear as the most reliable break cord that we can afford to buy. It has worked very well indeed up now.


> 1) but I never do SLs
> 2) what is a surgeons knot?
—————————————————————————————
From statement 1 I can understand question 2
Here is surgeon knot (well studied by us WELL BEFORE attempting our first SL jump (in our group))
Surgeon knot is a knot which minimize at best the curvature of line forming knot itself, so decreasing the minum possible the "Break Load of line loop WITH knot" with respect to "Break Load of simple line loop".
Surgeon knot it's on our "handbook"

jolly impossible? huh?

I know your not useing a surgeons knot in kernmantle nylon climbing rope, its just to give example. but the reason i dont use a multi-twist knot of any kind in rigging (rope rigging, not jumping) is the knots in-consistancy. the loops tend to fold over themselves as tensioned, sometimes even abraiding the outside of the rope. it does not 'invert' but it does fold over itself, and sometimes makes the 3 or 4 twists in the primary part of the knot useless to decrease the angle the rope bends.

this of course matters much less as the line gets smaller such as a cotton break cord, but In my opinion, break cord knotting is over-engineered. of course, it does not and cannot hurt.

my load cell is to big for a carry-along, but i could use it for an anchor.

> jolly impossible? huh?
————————————————————————————————————
Is your load cell capable to record the peak load at which break cord loop broke?
In any case, to do such a test you should put your load cell into the cynematic hain, i.e., between aluminum ring on parachute and bridle, and, again ,same load cell must be capalble of recording the peak force exerted in a split millisecond.

Yes, it a German Dynofor.

records real time readings as well as peak readings, can be hooked up to a computer to get a graph as well.

it weighs about 1.5 kg, so carry away is no good.