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Bars with PU tubing

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alford
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Bars with PU tubing

Postby alford » Sat Nov 02, 2019 5:16 pm

It's amazing to me how thin the actual depower line is inside the PU tubing. I don't want to pick at any specific brands here but was struck at its small diameter.
I understand it has to be this way or the PU tubing would be too thick.
My question is does the tubing add actual strength or simply offer protection against nicks and wear from the sheeting motion of the bar? I know, sand inside the tube can cause unseen wear too.
My intention is to understand and not troll a bare rope vs covered debate but I do know that if I used a bar with a single uncovered line of 1/8" Dyneema it would look quite delicate and probably draw remarks about being unsafe.

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Re: Bars with PU tubing

Postby Trent hink » Sat Nov 02, 2019 5:59 pm

1/8" dyneema has a breaking strength of around 2500 lbs. so it should be adequate.

The extra diameter in unsheathed depower lines is to account for wear.

I very much prefer to have the pu sheathing because I have had the experience where the unsheathed lines don't last more than a couple months, even with good care.

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BillyGoatGruff
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Re: Bars with PU tubing

Postby BillyGoatGruff » Sat Nov 02, 2019 6:58 pm

Most kitesurfing rope is Dyneema SK75, SK78 and occasionally SK99. Dyneema SK75 is weight for weight stronger than steel wire. To put it in perspective Tower cranes on big city building sites lift using steel wire which is weaker than Dyneema, they don't use the stronger dyneema because it is not as abrasive resistant as wire, and twists easier. Most depower ropes are in the range of 4 to 6mm. 4mm Dyneema has a typical braking strain of 1,400kg (enough to lift the average car with). There is simply no point in using thicker dyneema as you will never come close to snapping this rope if it's undamaged. The PU coasting offers no strength what so ever, it does however offer great abrasion resistance. If sealed properly the rope will last years on end, Naish have mastered this, the center ropes on Naish never snap and last years on end. You can thread a 4mm rope through 4mm (internal diameter) Polyurethene tubing by threading a much thinned rope through the tubing and pulling the new rope through, wet the new rope first to reduce friction, seal any ends with a small amount of melted candle wax.

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Re: Bars with PU tubing

Postby edt » Sat Nov 02, 2019 8:15 pm

typical chicken line is about 8x overstrength to compensate for wear. 3mm is plenty thick enough if there's no wear, so yeah it's fine if the PU tubing works properly and sand doesn't get into it. If it does get wear under the tube of course that's another story.

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Re: Bars with PU tubing

Postby iriejohn » Sat Nov 02, 2019 9:10 pm

edt wrote:
Sat Nov 02, 2019 8:15 pm
typical chicken line is about 8x overstrength to compensate for wear. 3mm is plenty thick enough if there's no wear, so yeah it's fine if the PU tubing works properly and sand doesn't get into it. If it does get wear under the tube of course that's another story.
Agreed, it certainly is another story because if it does happen the first thing you know is that the rope breaks.

I replace mine whenever I see that it's getting worn at the cost of a few $ and a few minutes no problem. I don't like surprises.

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BillyGoatGruff
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Re: Bars with PU tubing

Postby BillyGoatGruff » Sat Nov 02, 2019 9:16 pm

If it does get wear under the tube of course that's another story.
This seems to be the main issue of centre lines snapping between brands. North seem to suffer from broken centre line more than Naish and it's all to do with the end seals of the PU cover. Naish chicken loop rope is so tight in the PU cover there is no chance of sand getting in there and they never wear, the end connection is also super flush with the depower stopper.

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Re: Bars with PU tubing

Postby DIALS » Sat Nov 02, 2019 9:56 pm

Only ever had 1 bar with PVC tubing-Switch,,,The line inside will stretch and then the tube will become short..then the bar will get caught at the top of the depower and also caught at the full power,,,and its only single line so its more prone to stretch than the regular double line...I wont ever use the PVC tubing set up
again..

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Re: Bars with PU tubing

Postby mar menor » Sat Nov 02, 2019 11:33 pm

The best bar I have used and I have used a lot kiting for nearly 20 years

https://oceanrodeo.com/product/shift/

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Re: Bars with PU tubing

Postby deniska » Sun Nov 03, 2019 3:34 am

I have had CORE center lines snap on me w/o any visual cues.. Techtanium, my ass.. they are way too thin, no doubt..
CORE did replace the line under warranty, but did not dye my gray hair and did not repair the kite that ended up on a tree...
I think that non-transparent PU coating that allows water/sand to get in as bad design.. If you cannot inspect the line that carries the load, eventually you'll be paying for it... besides companies keep making bars too hard and expensive to repair.. recently I ordered 4 out of 20+ parts that a core bar consists of, and it was $95.. and that was for small pieces..not flying lines, CL assembly or actual bar, just a bunch of small ropes coated in plastic that don't last through 1 year..

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Re: Bars with PU tubing

Postby Herman » Sun Nov 03, 2019 9:03 am

Thin line and tubing seems to be associated with some very fiddly designs of rotor head. I would prefer to see a solid lump with 3 holes rather than a collection of plastic parts. The line - rotor head connection would be better out in the open imho. A bigger and grippier rotor would be easier to turn than a small neat slippery one!


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