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Harness hook broke during kiteloop

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metrox
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Harness hook broke during kiteloop

Postby metrox » Sun Apr 25, 2021 10:12 am

Today I had an accident. During kiteloop (approx 9-10m height) hook cracked completely. I am luckely ok, because I was using short leash and connected suicide mode. So kite catched me at some point and I not crashed so hard. I use Majestic harness with Stealth spreader bar ...
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It looks like it was cracked before and was slowly progressing till it breaks completely … Here possible to see some small corrosion from salt water. Also it is not possible to inspect hook, because it is inside (without disassembling it)
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And I am not a heavy rider. I weigh only 66-67kg.
I was thinking about possible reasons for cracks and complete breaks. And here not talk about Mystic brand, but I think this can be refered to any brand today.
There could be problems with applied load direction. Now with the new Stealth spreader bar hook sits nicely straight and not moves anywhere, but this makes another problem.
Days before it was like so :D
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So we see that applied load almost in complete tension to hook. Basically hook position can be aligned to applied vector load from the kite.
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Now if we look into the new harness and consider that it sits tight we can see such applied load vector. See below picture. (Actually like how good and tight SpreadBar sits and not moves anywhere)
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So in that case we not get pure tension on the support joint, but also some bending moment.

Being an Engineer I made rough fast calculations …
So 6mm bar 75mm length.
Image
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Used material S355 (don’t know what material used for hook, but this is not important here)
Design made for 1 bar (so total strength should be multiplied by 2)

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Image

Applied load here 2kN (approx 200kg) … So total applied load on 2 bars 400kg. 400kg because this is how much 1 line (approx) can hold :D
I modelled 4 situations when load applied on pure tension, and with some angle (20,40,60 degrees). Also the support joint is completely stiff and will not align with reality, because it can move on some degree … But as for example this is enough.
Image

We can see results (Utilization ratio). If load is applied in a little angle then it breaks and load bearing capacity is smaller 7 times. (This calculation not meant to be very accurate because I did it for 5minutes drinking some Whiskey and celebrating my 2nd birthday :D ) So we can see that our lines stronger than harness hooks :)
This is very important during kiteloops when you swing under the kite and it catches you. So the applied load vector could be even 90 degrees in some cases. And also it is dynamic load, not static …
Also there are a lot of reports from different riders on the internet about the same problem for any brand.
Example: https://www.wetestkites.com/2020/03/21/ ... our-lines/

So check your hooks and be safe ... And hopefully harness manufactures will stop save on material and think about riders safety ....

Cheers ...

P.S. This is new harness ... Ride with it from last year august and was on shelf during winter (approx 4 months in total)
Last edited by metrox on Sun Apr 25, 2021 12:48 pm, edited 1 time in total.
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Havre
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Re: Harness hook broke during kiteloop

Postby Havre » Sun Apr 25, 2021 10:46 am

Thanks. Interesting post.

How can you check it?

metrox
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Re: Harness hook broke during kiteloop

Postby metrox » Sun Apr 25, 2021 10:48 am

If you have Stealth spreader bar than you need to open up it and check on cracks.

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Re: Harness hook broke during kiteloop

Postby Kerplow » Sun Apr 25, 2021 10:56 am

Have two local examples like this on the same brand :/ How to be sure that mine is not cracked?

metrox
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Re: Harness hook broke during kiteloop

Postby metrox » Sun Apr 25, 2021 11:04 am

Back of spreader bar you have 4 screws. You need to unscrew them and then you will see this part. So you will be able to inspect hook on cracks.
Image
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Re: Harness hook broke during kiteloop

Postby elguapo » Sun Apr 25, 2021 12:33 pm

my steath spreader broke 1st season of use (to be fair, was a pretty heavy user that year)
...i was downlooping a transition (low end wind range om a 3m peak4....not heavy forces at all)
i know at that moment was not exactly pleased since kite crashed immediately in water and i had no chance at relaunch (was behind a reef and had a not-fun swim back to shore

i'm not a physics or material science guy...

but do this lines/wire have a wear limit?
..is it a known that 'this or that' will break after x amount of uses/time on the water?

metrox
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Re: Harness hook broke during kiteloop

Postby metrox » Sun Apr 25, 2021 12:40 pm

This is something what should last forever :)) It is steel :D I see that problem with this hook that they increased length of it, because it is more inside under plastic cover. And also problem what I was described above. Well basically it is not enough material there ... Idk is it big saving in material, but its would be much safer if they put solid peace.
Here my 30min design. I think this would last forever :)
Image

And you can open beer with it between sessions :lol:
Image
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Re: Harness hook broke during kiteloop

Postby SMJ » Sun Apr 25, 2021 12:46 pm

It continues to boggle the mind how our sport is still plagued with these medieval hook & loop systems.

metrox
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Re: Harness hook broke during kiteloop

Postby metrox » Sun Apr 25, 2021 12:54 pm

NeilPryde had something really strong almost 10 years ago :) this looks really proper design.
You can hook elephant on it and its will be ok :))))
Image

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Re: Harness hook broke during kiteloop

Postby matth » Sun Apr 25, 2021 1:01 pm

Or consider a closed hook/loop if you do not unhook..


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