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Simple short line extensions - is a figure-8 knot ok?

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mister-z
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Simple short line extensions - is a figure-8 knot ok?

Postby mister-z » Thu Sep 24, 2020 6:56 pm

I know most of you gear builders are doing stuff like carbon fiber foils, but we all have to start somewhere, right?

I bought this 1.8mm Dyneema from West Marine with the intention of making two short (~8cm) extensions to lengthen the front lines of my Peak4. Intended to splice a loop in each end. Have never spliced line before, so was excited to learn something new. Then when I got home I realized the line isn't hollow. So instead of learning something new, I just doubled it back on itself and tied a figure 8.

My question is, is this a bad idea? Anything unsafe about this?

Here's a photo of the non-hollow line and loops I made with it, and a photo of how it attaches to the kite (on the left) and to my fly lines (on the right).
PXL_20200924_173558092.jpg
PXL_20200924_175032981.jpg

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Re: Simple short line extensions -- is a figure-8 knot ok?

Postby tkaraszewski » Thu Sep 24, 2020 7:05 pm

Next time look for "single braid" instead of "double braid" if you want hollow line.

If you think that the line for these loops is strong enough in general, then you should be fine. The knot is in doubled line, so even if it reduces breaking strength by half, that's half of two lines which is back to the original breaking strength of the line.

mister-z
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Re: Simple short line extensions -- is a figure-8 knot ok?

Postby mister-z » Thu Sep 24, 2020 7:31 pm

tkaraszewski wrote:
Thu Sep 24, 2020 7:05 pm
The knot is in doubled line, so even if it reduces breaking strength by half, that's half of two lines which is back to the original breaking strength of the line.
Thanks, that's the kind of advice I was hoping for -- not just "looks good" or "horrible idea," but "here's how to reason about things."

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Re: Simple short line extensions -- is a figure-8 knot ok?

Postby jakemoore » Thu Sep 24, 2020 8:31 pm

Whats the breaking load on the line?

Also, if you have a polyester covered double braid, the polyester may cut through the dyneema lines on the kite.

I would be more inclined to do something like this on a rear line or up in the bridle. Less likely on a front flying line where it may need to support several times my weight in loading up for a jump or transition.

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Re: Simple short line extensions - is a figure-8 knot ok?

Postby Toby » Thu Sep 24, 2020 8:50 pm

if breaking load is ok, it should work fine.
Had several extension like that already, although with a bit thicker line.
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Re: Simple short line extensions - is a figure-8 knot ok?

Postby TomW » Thu Sep 24, 2020 9:11 pm

It looks like you bought a sheathed line. To do a splice you need braided, dyneema is best.
Premium ropes has a great app with videos showing how.
A splicing fid is recommended, but with small lines a thin steel wire, bent in half to form a loop works ok for a few splices.

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Re: Simple short line extensions - is a figure-8 knot ok?

Postby edt » Thu Sep 24, 2020 9:50 pm

Figure 8 is fine for this type of line you are well within spec

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Re: Simple short line extensions -- is a figure-8 knot ok?

Postby mister-z » Fri Sep 25, 2020 12:25 am

jakemoore wrote:
Thu Sep 24, 2020 8:31 pm
Whats the breaking load on the line?

Also, if you have a polyester covered double braid, the polyester may cut through the dyneema lines on the kite.

I would be more inclined to do something like this on a rear line or up in the bridle. Less likely on a front flying line where it may need to support several times my weight in loading up for a jump or transition.
This is specifically for a small Peak4, which I only use for cruising and carving, won't be subject to high loads. I agree -- if it were for a kite that I boost with, I'd give myself a healthy margin of extra strength.

Why is polyester liable to cut through Dyneema? Is it too abrasive or something? Looking now at West Marine's website, I think it may indeed be a polyester sheath. I'll replace with single braid Spectra or Dyneema. Guess that's $1.59 down the drain.

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Re: Simple short line extensions -- is a figure-8 knot ok?

Postby Trent hink » Fri Sep 25, 2020 12:56 am

Wait.... What?

Dacron polyester has been the standard sleeving material for flying lines since the birth of this sport.

Got to agree with the second part though. Shortening the rear attachment on the kite would be simpler and cleaner.

I'd just slide the metal ring up the rear bridle to double it up and and then tie a fiqure 8 in it.


jakemoore wrote:
Thu Sep 24, 2020 8:31 pm
Whats the breaking load on the line?

Also, if you have a polyester covered double braid, the polyester may cut through the dyneema lines on the kite.

I would be more inclined to do something like this on a rear line or up in the bridle. Less likely on a front flying line where it may need to support several times my weight in loading up for a jump or transition.

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Re: Simple short line extensions - is a figure-8 knot ok?

Postby jakemoore » Fri Sep 25, 2020 9:54 am

http://fighterkitecentral.com/pdfs/spec ... 20line.pdf

The line with the lowest melting point gets cut.

Dacron sleeved lines are sold by companies whose kites have beefy double braid line terminations.

Flysurfer terminations on the kite and bar lines are thin spliced UHMWPE with no sleeve and no double braid.

———

Trent Hinks suggestion is elegant. There also may be a solution hidden under the bar float or in the end of the bar. .
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