Power Kite Forum - Backyard Spectra Test

Backyard Spectra Test

tsteigs - 28-9-2018 at 08:34 AM

I was curious about the strengths of various ways of forming loops in the end of flying lines. So, with 50 meters of Jerry Brown 500# hollow braid spectra, a come-along, a crane scale, two carabiners and a couple of oak trees I ran some crude tests. By no means are these numbers precise, but the relative values proved interesting.

The breaking strengths were as follows:

Overhand knot...............................198#
Figure 8 knot.................................210# (knots slipped)
Figure 8 + overhand lock.................245#
Sleeved figure 8 w/ 200# dacron......264#
Sleeved figure 8 w/ 500# dacron......300#
Sleeved + Sewn loop......................215-425#
Short eye splice + lock stitches........415#
Long Self locking splice...................480#

On the sleeved and sewn loops, I set up a jig on the sewing machine, and adjusting the stitch width only fractions of a mm made a huge difference in the stress they would take before unzipping. The professionals are clearly much better at it than I am.

The difference between un-sleeved and sleeved figure 8 knots was surprisingly small. Re-running this test several times didn't change the outcome very much.

The long self-locking splice was explained on a youtube fishing video: https://www.youtube.com/watch?v=kJU87450cqM&hd=1%2F

Tapering the buried end of the splices at for least 1 inch made a significant difference in the breaking strength. When they weren't tapered, they broke every time where the buried portion stopped.

My apologies to engineers who are cringing and in pain from these crude methods.

Edit: After playing with these lines for a while, the splices started creeping apart. I bow to the wisdom of this forum and will start using the Brummel or long bury splice with stitches. www.chicagoyachtrigging.com did destruction testing on dyneema and found the long bury with stitches beat the brummel but that both were very good.

jeffnyc - 28-9-2018 at 09:23 AM

Awesome you took the time to do that. A bunch of folks have also done these tests, and just glancing at this it looks like you've come to the same conclusions they have. Knots in your lines weaken them, sleeves are used to protect the lines from wear (and I think help with the sewing), and the long tapered splice is the strongest. If you use that splice you'll want to toss a couple stitches in to hold the loop (the stitches do nothing for strength - you just don't want your loop loosening if your lines go slack). the alternative is the Zacher, where the knot holds the loop and is easily adjustable as your lines shrink.
The usual splices are Brummel, Zacher and straight eye splice (is that the name for that one?). Always do the taper, it seems the abrupt change makes a definite weak point. And the longer bury also gives more strength up to a certain point.
I believe if you use Jerry Brown, you will want to pre stretch your lines.

tsteigs - 28-9-2018 at 10:28 AM

Jeff - Thanks. You are right. This is nothing new, but I enjoy tinkering and needed something to do on a day with no wind.

One additional test was seeing how much strength was lost using the larks head knot to attach the line to a leader line.

Using a 3.8mm 12 strand Dyneema SK78 as a leader line, the unsleeved line started breaking at around 350#. What was more surprising is that after about 10-15 tests ( I didn't count) the leader line snapped! You wouldn't think that at 1300# breaking strength it could possibly be a weak link. Aparently, cumulative fatigue can occur fairly rapidly in Dyneema.

Kamikuza - 28-9-2018 at 05:12 PM

"Long Self locking splice"
Brummell? Can't tell from the video :D but your results line up with the other couple of tests I've seen.

Splice FTW!

Memopad - 15-10-2018 at 04:06 PM

When you start destructive testing dyneema/spectra line, the majority of failures are from the line actually melting. As you've discovered some of the knots will slip as the line is too slippery to hold a traditional knot. The other failures will be from the line slipping through the knot, but the friction heats up the line till it fails.

There are a spectra specific knots that have been designed to minimize the slippage from traditional knots, but even the best knots will cut line strength by 50%. Splicing is the way to go, though a properly sleeved and sewn loop can be really strong.

The locking brummel is an easy splice and is self locking. The key to the strength of a good brummel splice is still in the buried tail portion of the splice. All splices in spectra need a really gradual taper in the tail bury.

There is a ton of interesting info on spectra on sailing forums, but we usually don't deal with splicing line nearly as thin as kite line.

tsteigs - 16-10-2018 at 02:51 AM

OSHA (https://osha.oregon.gov/edu/grants/wrd/Documents/osuforest/r...) did some destruction testing on AmSteel-Blue and found the following knot breaking strength in spectra lines:

Figure 8 ................................ 33%
Bowline ................................ 33%
Taught line hitch .................... 39%
Double Stevedore .................. 49%
Cow Hitch (Larks head)........... 57%

Does this mean that our 600# flying lines are really going to break at (600 x 57%) 342# when we connect them via Larks head to the kite and Leader Lines?

If this is true, would it make sense to splice some 1,000# spectra to each end of the flying line? So, instead of ending the 600# in an eye splice, splice on a few feet of 1000# and terminate the 1000# in an eye splice. The end to end splice (long splice) has a breaking strength of 85% in spectra which would break the 600# line at 510#. The Larks head in the 1000# would break at 570#. Would this simple fix increase the effective breaking strength of our flying lines from 342# to 510# ?

nate76 - 16-10-2018 at 06:13 AM

tsteigs, great thread - thanks for sharing!

I actually became really interested in knots for dyneema a while ago. This last winter I had the misfortune of having a line break when I was in the back country kite skiing and I realized I didn't have a good way of tying the line back together. Felt kind of stupid, because every knot I made slipped out. Fortunately I only had about a mile to hike out, but it made me realize I needed to learn an easy knot that I could use in case this happened again.

So I did some testing this summer and found out the answer was not as straightforward as I had hoped. The assumptions I made was that it would be a sacrificial knot - I didn't really care if I could get it undone - for the purposes of limping back home in an emergency. My criteria was 1) an easy knot that 2) also didn't use a lot of line length so that the kite would remain relatively stable, especially if it was front line, and 3) strong enough to hold a front-line break.

I tested some simpler/shorter knots like the Figure-8, Carrick, and Zeppelin knots and found they would all slip with Dyneema if trying to support my own weight - about 200 lbs. In the end I found I had to go to a triple fisherman's knot before I could get one to hold.

I think in a pinch you could use the Carrick or Zepplin knots on your outer lines, since they are not carrying much load. I'd be curious to know if you or anyone else has done any testing on this though, and found good solutions?

FWIW, the following website has some great knot tutorials: https://www.animatedknots.com/doublefishermans/

tsteigs - 16-10-2018 at 07:45 AM

Nate76 - Sorry you got stranded. Sounds like your triple fisherman knot experiment proves promising. Thanks for sharing your test results. BTW, love the videos on your site.

I've not done any testing, but disecting the knots on a Longstar2 kite, the primaries are tied to the sail with a simple slip knot plus an overhand knot as a stopper. However, what seems to keep the whole thing from slipping out is a dot of glue on the overhand knot. From suggestions on the internet, it appears that the most applicable glue is some sort of thin, flexible CA such as Bob Smith "Insta-Flex".

The LS2 primaries are tied to the secondaries with a "Bridle Knot" (see picture from kiteplans.org site), again backed up with an overhand knot plus CA.

You probably won't be carrying a bottle of glue with you every time you fly, but perhaps a length of spare bridle line stuffed in your kite bag may prove useful. Maybe if you tie any of the knots you mentioned, plus an overhand stopper, plus leaving enough tail after the stopper, you could at least fly the kite back to the car.

PistolPete - 16-10-2018 at 09:47 AM

Quote: Originally posted by tsteigs

OSHA (https://osha.oregon.gov/edu/grants/wrd/Documents/osuforest/r...) did some destruction testing on AmSteel-Blue and found the following knot breaking strength in spectra lines:

Figure 8 ................................ 33%
Bowline ................................ 33%
Taught line hitch .................... 39%
Double Stevedore .................. 49%
Cow Hitch (Larks head)........... 57%

Does this mean that our 600# flying lines are really going to break at (600 x 57%) 342# when we connect them via Larks head to the kite and Leader Lines?

If this is true, would it make sense to splice some 1,000# spectra to each end of the flying line? So, instead of ending the 600# in an eye splice, splice on a few feet of 1000# and terminate the 1000# in an eye splice. The end to end splice (long splice) has a breaking strength of 85% in spectra which would break the 600# line at 510#. The Larks head in the 1000# would break at 570#. Would this simple fix increase the breaking strength of our flying lines from 342# to 510# ?

That was my idea too

http://www.nwkite.com/forums/t-11649-0-asc-17.html

Built in pigtails :smilegrin:

tsteigs - 16-10-2018 at 10:39 AM

PistolPete FTW!

nate76 - 16-10-2018 at 12:38 PM

Thanks for the info on the Longstar Bridles - that's interesting. Carrying an extra piece of line seems like a smart idea; I also started carrying an extra pigtail that I could put on the shortened-line side to even the lengths out again.

You're post has got me thinking about this again. Was doing some more research this morning and might have found an even more promising knot that is pretty simple and uses up less line, called a Modified Carrick Knot, or First Bend. I had it supporting my full weight this morning without a hint of slipping:

I don't want to hijack your thread, so might just start a new one, but appreciate all the info.

For anyone interested on this thread though, here is a link to making the knot:

https://www.youtube.com/watch?v=o82mmdoIrvY

tsteigs - 17-10-2018 at 02:28 AM

Good find on the First Bend. Nice tool to have in the bag of tricks.

Factory Pre-Stretch

tsteigs - 17-10-2018 at 02:39 AM

There are lots of suggestions on the forums about how to pre-stretch lines at home, but does anyone know how the manufacturers do it?

I tried stretching the 500# Jerry Brown line with body weight and then pulling it with the car with a weak link breaking at 250+/- pounds. The lines were still springy.

Back out with the come-along and crane scale to keep a 23m line loaded at 60% (300#) of rated breaking strength. After reaching 300# pull, it stretched 51mm in the first minute, and 32 mm in the second minute. By the 15 minute mark, the stretch rate was less than 6 mm / minute.

Tomorrow I hope to test its elasticity vs Flysurfer lines.

It would be nice to know exactly what the manufacturers do so we could replicate it. Any ideas?

Testing Pre-Stretch Methods

tsteigs - 18-10-2018 at 08:32 AM

Starting with 4 fresh lengths of 25meter long, 500# Jerry Brown spectra, I tested 3 pre-stretch methods: With one end of the line tied to a tree, at the other end: 1) A carabiner plus a pulling rope wrapped around my waist and pulled as hard as I could and bounced against it for 2 minutes. 2) Pulled with a truck using a 250# weak link for 2 minutes before breaking the link. 3) Come-along + scale and held a constant force of 70% (350#) of rated breaking strength for 20 minutes. After resting the lines, here are the amounts that the lines were permanently stretched:

Control Piece ......................... 0mm
Hand Pulling...........................506mm
Truck Pulling...........................540mm
70% (350#) for 20 min............602mm

Assuming that the - 70% (350#) for 20 min - test removes nearly all of the creep, this would demonstrate that more than 80% of the total creep can be removed with just a few minutes of hand or truck pulling. However, doing this will leave 100 +/- mm of creep that will show up during the flying season.

Edit: I went back and tried to apply 80% (400#) of tension for 20 minutes. My bad. After about the 11 min. mark, the line failed and ruined over half of the length showing puckers and bulges.

Flysurfer Lines VS Jerry Brown Spectra Elasticity

tsteigs - 18-10-2018 at 09:21 AM

From what I understand, one of the defining characteristics of a good flying line is minimal elasticity (the opposite of being a rubber band). To determine whether or not spectra fishing line is a good substitute for commercial lines, I wanted to test its elasticity against a high quality line.

Using the Jerry Brown lines that were just pre-stretched, and a pair of factory lines off of a Flysurfer Peak2 6m that has been flown 6 times (thanks Cheddarhead) I tried to simulate an extreme flying situation to test line elasticity. The lines were held at 50# force for 30 seconds and then at 150# force for 30 seconds and the amount of (temporary) elongation between the two conditions was measured.

Here is how much elasticity they exhibited:

Control Line (not pre-stretched).............440mm.......( 17.6inch)........1.79%
Hand Pulled.........................................306mm.......( 12.0inch)........1.22%
Truck Pulled.........................................287mm.......( 11.3inch)........1.15%
70% (350#) / 20 min............................245mm........( 9.7inch).........0.98%
Flysurfer Front Line...............................213mm........( 8.4inch).........0.85%

The percentage column represents the amount that the lines elongated as a percentage of total line length (all results have been normalized to 25m lines). It can be assumed that some of the elongation of the first 3 lines was due to stretch (creep) and some was due to elasticity. The line pre-stretched at 70% of rated breaking strength for 20 minutes probably comes close to the true potential of the Jerry Brown 500# line when nearly all of the creep has been removed from the lines.

Under the best pre-stretched condition, Jerry Brown 500# spectra and the Flysurfer lines both displayed less than 1% elasticity. On an absolute basis, the difference was approximately 0.128%. On a relative basis, Flysurfer lines were 13% less elastic than the Jerry Brown spectra lines.

To be fair, the Flysurfer front lines are 660# breaking strength and the Jerry Brown lines are 500#. I do not have any Jerry Brown 800# on hand, but it is possible that this heavier weight line could demonstrate less elasticity in this test and compare even more favorably to the Flysurfer lines.

* None of these tests are meant to represent engineering / scientific accuracy, just the crude results from a guy with too much curiosity and too little wind.