Independent harness stress test – the naked truth

Harness stress test; the naked truth
Harness stress test; the naked truth

What a feeling to deliberately abuse and demolish half a dozen brand new harnesses. For a good cause though; make kiting another step safer. Did you ever realise a harness hook can fail? Or that a spreader bar is getting the shape like it is made for some one with a huge belly? We thought of it being a serious issue late 2019 when we read people got into some nasty situations due to broken or bent hooks. It got our attention even more when we started tracking the numbers. Over 70 people all over the world reported broken or seriously bent hooks or spreader bars. And those are just fairly new ones -mostly 2019 versions-. The matter -particularly for the kiters that are either heavy and/or ride in stormy conditions- calls for an independent investigation. These are the eye opening unique -but above all- independent results.

Existing knowledge

It took us quite a bit of effort to understand what is -and isn’t- already being done to develop and evaluate the quality of a harness. It was weeks after finishing our test we got the information a static test is going to be overruled in the near future by a dynamic -and much more realistic- one. We also left in the dark by the harness producers if a temporary elongation is something good or bad. Neither one of them told us a number on what they believe is the maximum real-life load force.

So the one uttermost important result is that we put up a mirror to the industry. The explanation from some brands it could be due to ‘an incidental bad produced harness out of the thousands we produce’ is really not something we want to hear. Overdimensioning and safety margins is evident for such an critical part as a harness hook.

The results

In order of importance our results;

Result number 1: The test isn’t 100% correct.

None of the hooks broke off their spreader as we had seen in many cases in real life. We -and the kite industry- are not doing it completely right. If that is hard to understand please read the post on the method. We are assuming that a super high static load can tell us something on the strength of a hook while it’s real load maybe lower but at a much higher (thousands probably) number. We also assume bending is a bad thing. Maybe we are way off but let the industry come up with thorough and clear explanations. In the future we may end up with numbers visible stated at each product on strength. Like we now start to get on kite lines. Probably on the long run even based on an ISO standard. But hopefully the industry is mature enough not to wait for that.

Result number 2: The ranking.

Manera is the clear winner of our test. Most likely it is not because they use special materials but probably get its positive results in our test due to a relative short hook. More details can be found at the end of this article.

Result number 3: The iron heart is very strong.

An reassuring result -although it has nothing to do with the strength of a harness- is that the Duotone (previously known as “North”) Iron Heart did not flinch. Not even once out of the roughly hundred times we used it to pull on each harness up to 600 kg it failed on us (while the demands in the ISO 21853:2019 standard on release systems is to withstand only up to 240 Kg).

Four tests

What we did wasn’t much different from what brands have been doing when they test the strength of their harness hooks or spreaders. The industry standard is -roughly- just a static pulling force. We used a four stage test program. By altering the pulling angle in different ways. from straight forward, slightly upward by pulling on only the lower positioned part of the clips, on the lower clips but with the pulling angle side ways (to simulate a kite being upwards and side ways) and with the spreader only connected to one clip. The full test description is available in a separate article.

Four stage test program
Four stage test program

Details on the test results

Harnesses in the test:participants

Temporary bending spreader bar at test one.

Permanent bending spreader bar at test one.

Temporary bending spreader bar on all tests

Permanent bending spreader bar on all tests

Temporary elongation hook on all tests

Permanent elongation hook on all tests

*The Ion spreader broke in test one around 575 Kg. The clips broke at test stage 3 and 4 both at around 550 kg (therefor three different Ion hooks have been used).

Pictures of the hooks and clips after all tests


  1. I don’t think bending is a good indication of the safe limit of the hardware. The problem is that metals that don’t bend can be brittle and so can break at a lower load even though they may bend less than a metal that may not break at the same limit. A bent and not-reusable hook is a very different danger than a hook that breaks and lets go, so this test could actually penalize a safer hook.
    For example, I am currently using my ride-engine spreader bar set up with a ring on a surf-loop dyneema line. That dyneema line is very strong, and so is the ring, but the retainer for the dyneema is only the plastic body of the spreader bar and is NOT backed up by the internal metal bar, so the eventual failure will be that the dyneema could just rip out of the spreader bar with no warning at all and dump me suddenly. If you use the dyneema at the center (so no sliding) that IS backed up by the internal metal bar, so the same failure can not happen.

  2. Interesting. I’ve actually seen two kiters in the Boston area break loose their harness hooks, both looked like corrosion, one looked like the weld gave up maybe due to corrosion too.

    I’ve always used a NP harness, the spreader bar and hook are all solid machined aluminum so they can’t corrode, and also there’s no weld, the hook is bolted to the spreader bar (maybe I should inspect those bolts).

    Was hoping to see how the aluminum spreader bar/hook compared to the steel ones in your test.

    Great work thanks for taking the time to do this !!

  3. Martin’s comment is very interesing. In my case I broke the hook in a non soldering point but I could see rust inside the metal (quite astonished). Previous to breaking it I thought it was only cosmetic when I saw it on the outside.

    Several pictures posted by WTK of used harness also shown rust in the breaking points.I thought it was only me because I did not rinse it regularly.

    Thanks WTK for these series of articles. I wonder if it could be possible to make something similar about construction of kites. I think it would be very interesting to have the views from a kite-repair sbop point of view.

  4. Interesting test. However struggling a bit to get a clear conclusion for the 70+ broken hooks which has been counted as starting point for the investigation. I believe the conslusion of your great work is that the ISO standard and static testing is not representative for the real exposure of the hooks whilst kite surfing. Based on this fact finding we strongly encourage the insdustry including ISO to adapt.

  5. Thanks for the tests!

    The mayor problem is breaking hooks. Your tests did not break any.

    To me the most important conclusion is:
    Metal hooks are not a reliable way to attach yourself.
    Especially when used in salt water.

    I removed my hook and attached a 5mm Dyneema (2300kg breaking strength!) in the centre of my spreader bar.

    Some brands (I know Mystic) have sliding bars with a centre rope.

    A metal hook is only useful if you are in kiteschool or like to unhook.

  6. This is a good article.
    Yes, there are variables missing that could be helpful and important but here is SOME evidence that spins both a concern to some degree but also some confidence about the products punters are using.
    Some other variables I’d like to see are stress in different temperatures. Wind chill factor, water temperature, number of times used.

    I’ve seen plenty of broken hooks in my time. It simply reminded me to replace my harness semi regularly. Maybe if I sell my harness I’ll suggest to the new owner that it may need a new spreader bar.
    Thanks for the info.

  7. i think the failure number is the best way to chose or avoid a brand. (With all statistic problems, eg. how many are in use)

    Your load tests are nice and correct but even if there is a correlation to the failure number, i don t think that there is really a causality.

    Beside i would also not recommend to use a deformated hook 😉

  8. Hi Martin,
    the failure numbers do not suggest it is not a complete lottery. Ion did a recall. There must be a reason for that to say the least.
    RE spreaders bent quite easily. Which all leads to the assumption the are quite some differences between the harnesses.
    We just get the story started by stating some results. Not saying they are correct but do saying the ‘lottery’ needs to get sorted out.

  9. i had to add:
    You can also not say “a stronger harness is stronger” cause in the end it decides the welding process and the lottery of luck, if a stress corrosion crack occurs. When it happens, there can be for example 10 Newton of force be enough to lead to the completely destruction and risk of life.

  10. Hi Martin,
    Thanks for thinking with us. You are 99% right.
    Two remarks though, if bending means it is the start of a breakage using this bar or hook would mean a potential risk. We happend to be out kiting this week in 50knots. The last thing we want is worry about a harness failure.
    The other remark would be; yes indeed this is far from a optimal test.
    But what else (brochure, websites or an indication on the product for example) is out there to refer to if you want to know the strength of your harness?


  11. Hey, nice test but it dit not realy catches the problem. I have seen already some bend hooks and even mine has not the original geometry anymore.
    You can see it, you can replace it and even if u would use it for a few more sessions there would not be any problem as long it is still is a kind of hook.

    The real problems are “stress corrosion cracks”. Nearly every broken hook is caused by this problem and it s quite a huge problem. You take a material like v4a, you destroy the crystal structure by welding and add something like salty water and here u are.
    At the end of the production is nearly no possibility to do a specific quality check, cause the part with the salty water comes later while using and it takes some days, months or years. The User can t see inside the material and a rusty surface on the welding is not always visible before it cracks. On the other hand nearly every harness gets some rusty surfaces at the welding without any serious stress inside the crystal structure, so you can t replace all harnesses with visible signs. To completely avoid rust at welded v4a steel in contract with salty water is also illusory cause you would need a very stable production process which is only possible with robotic and high invest. Not rentable to produce a few harnesses.

    Back to the article (or the 3 articles about this topic) i think it leads to misinformation if you focus on the nearly irrelevant aspects of static and dynamic load and forget the key problem “stress corrosion cracks”.


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