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 Post subject: Re: By how much can kite lines increase over time?
PostPosted: Thu Dec 19, 2013 11:13 pm 
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Joined: Fri Jul 16, 2010 6:27 am
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Location: Ford Lake, Michigan
Not short trim short leaders I run out of knots and don't mind tuning the bar


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 Post subject: Re: By how much can kite lines increase over time?
PostPosted: Fri Dec 20, 2013 12:58 am 
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Location: Vancouver, Canada. rides Naish,Ozone,North, Spotz,Aguera
When you buy a good set of pre stretched lines from major companies like Naish, North, Ozone etc. you get very little stretch. I do jumps and kiteloops when I kite and I put lots of load on my lines and I rarely see more than a couple centimeters of stretch on the centre lines. It is easy to correct for this by moving the rear leader line knots.

Most kite lines are Spectra which is a a brand of ultra-High molecular weight polyethelene line and has well known stretching properties as shown in the graph below. (Dyneema is another brand but stretches even more.) As you can see from the graph, when a manufacturer pre-stretches by 3% then the lines exhibit little further stretch.

Attachment:
graph.jpg
graph.jpg [ 14.33 KIB | Viewed 388 times ]


Q Powerline is a spectra product that has linear filaments through the middle rather than the hollow core braid that most kite lines use. Q powerline stretches like any line (I have personally run tests on it to the breaking point). The main feature of Q powerline is that it can be knotted with somewhat less loss of strength than braided line.

I hear reports that a hollow core braided line can "shrink" slightly under certain conditions. But I am skeptical that the rear flying lines on an inflatable kite would shrink as there is normally significant tension on them. And most of us "rinse" our lines often enough that dirt is not an issue. If anyone has actual measurement data on this it would be interesting. I find no data on this from the manufacturers.

Anyway, it is certainly always wothwhile to check your lines and set them all equal.

:wink:
Chris Glazier


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 Post subject: Re: By how much can kite lines increase over time?
PostPosted: Fri Dec 20, 2013 2:54 am 
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Thanks for that info cglazier

It corroborates my experience with new never pre-stretched spectra, and with the behavior of my lines after they have been stretched (or came from the factory properly pre-stretched).

I don't think I'll ever be able to observe shrinking lines by dirt. My main spots has small rocks, dead seagrass, asphalt and virtually no dirt or sand (but we love it anyways).


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 Post subject: Re: By how much can kite lines increase over time?
PostPosted: Tue Feb 11, 2014 1:29 am 
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Joined: Mon Oct 13, 2008 3:51 am
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Location: Ridgway
I too am realizing that I've got uneven lines, including uneven front lines. I'm hoping equaling lines lengths will make my kites feel new! I've done the adjustments via extra pigtails here and there on a couple of bars now.

I like Oldnbroken's analogy and approach to rotating fronts and rears just like tires. So, that makes me think, why not "balance" too. Maybe it's better to re-stretch lines to the same length versus slapping on pigtails. Maybe do this twice a season. I think I want to build a little puller to pull all 4 lines at the same time. Has anyone tried this? Any idea to what force and what length of time to allow for recalibration stretching? I'm thinking 25% rated strength for several hours.
Ergo, 600lb line x 25% stretch load x 4lines = 600lbs. Hey, easy math!


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 Post subject: Re: By how much can kite lines increase over time?
PostPosted: Tue Feb 11, 2014 2:03 am 
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Quote:
a little puller to pull all 4 lines at the same time

looks like
Image
But I recommend doing it one at a time
I've used a 6:1 tackle left over from the windsurfing era.
Hanging my weight (~82kg) on it could be too much for 360kg lines, so I just pulled it hard: the average fit man can pull with a force of about 35dan/75#.
This produces a force after friction loss a bit over 450lbs/210kg, plenty to prestretch lines.
A minute or less, not hours, will do the trick.
Once it stretches, it is stretched.
You really only need/want to put 60% or so of rated load into the line.
If you needed to prestretch a heavier line, you could just string it between 2 very strong points, and stand on it. This would give a mechanical advantage of 7:1, if the line was "straight" in the first place. But it also would place you in the firing line of the broken line, if it snapped, with 1100lbs/~500dan of tension in it.
Keep in mind a bowstring with 20-30dan will fire an arrow that will kill a moose.
So whatever you do, do not hook a line to be stretched to anything that could become a projectile.
Attach it to another, stronger line, tied around a tree or something that will not move.
And lead the tail of your tackle off at an angle so you are out of the "line of fire," never hurts to be cautious.


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 Post subject: Re: By how much can kite lines increase over time?
PostPosted: Tue Feb 11, 2014 2:46 am 
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Joined: Mon Oct 13, 2008 3:51 am
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Location: Ridgway
BWD,
You're right about using the bar as a puller. In the pattern of using old windsurfing gear, I was thinking about using a boom harness loop to latch on to both sides of the bar to pull it down to the chickenloop. Then use a come-along or a block-and-tackle to pull. Is there no argument for simultaneously pulling on all 4? How can you assure equal lengths if you pull individually? Also, my hunch is that there might be a material memory that could recoil if not left on for "a while". But that's just from theory, not actual practice. Being an engineer (please don't hold it against me!), I'm going to have to perform an experiment...


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 Post subject: Re: By how much can kite lines increase over time?
PostPosted: Tue Feb 11, 2014 3:05 am 
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Joined: Mon Dec 03, 2012 6:38 pm
Posts: 35
Location: Southern Ontario
http://vimeo.com/46833653

Found this video from another post quite helpful when trying to tune my bar. I was quite shocked
at the difference in my line lengths, 3 inches on one line. Kite flew way better after
I got the bar dialed.


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