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Munter Hitch QR

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Herman
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Re: Munter Hitch QR

Postby Herman » Tue Jan 28, 2020 5:58 pm

I doubt that the normal forces and coefficient of friction know whether they are knotted or spliced.

Interesting that the bowline slipped under load. Interesting to speculate the speed of slippage compared to load characteristics. Would it have continually slipped faster as the load increased or would it bite at some point and not slip etc.........

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jakemoore
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Re: Munter Hitch QR

Postby jakemoore » Tue Jan 28, 2020 6:27 pm

I had about a 3 cm bitter end so as not to have too much flopping around around the quick release. Maybe the knot can cinch down better if there is a longer bitter end?

I would propose for early water trials a long bitter end e.g. 20 cm and some marks with a sharpie marker would help detect slip early.

One experiment I tried to eliminate the pin was to make a composite termination of the Amstel depower line with epoxy and heat shrink. In essence the rope becomes the pin. Its still too flexible.

I am interested in this concept of ditching the pin.

My solution to my bowline problem was to use different line. At the time I moved to polyester/dyneema Paraloc lines. I don't know if they are available any longer. I continued to put an overhand knot stopper in the bitter ends of a bowline since I'm motivated to avoid gear failures.

Herman
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Re: Munter Hitch QR

Postby Herman » Tue Jan 28, 2020 6:57 pm

Jakemoore

I am not dismissing your concerns and I am not saying the munter idea will definitely work but at the moment I still think it is worth looking into.

In my old climbing circles nobody used bowlines because they are notorious for coming loose. We would much prefer figure of eight. I have been riding with dyneema for many years and I am struggling to remember any incident of knot slippage. I used to use insurance stitching with knots but now this is rare. However I do set my knots hard often using leavers. I do not use bowlines in kite rigs. Fine for boats where a long tail or stopper knot is appropriate.

Figure of eight loops can be tied through a ring by tying a figure of eight in the standing part passing the bitter end through the ring and then follow the end back through the loops of the eight. Set hard and then way more robust than a bowline. Cow hitching the ring or bail is also sensible.

Regards Herman.

Ps if I was forced to use a bowline with 3cm tail I would stitch the tail in place and probably put some stitching through the bite. One of the best things about a bowline is that it is extremely difficult to set them really hard, good for boats - bad for kiting and climbing!

If and when I get round to trialing I will start in a buggy where it will be easy to jiggle and abuse the little munter!!!!

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Re: Munter Hitch QR

Postby Matteo V » Wed Jan 29, 2020 12:20 am

Herman wrote:
Tue Jan 28, 2020 5:58 pm
I doubt that the normal forces and coefficient of friction know whether they are knotted or spliced.
Friction, deformation, and stretch extremely different in dyneema / Spectra versus nylon and Dacron.

For instance, when making a bend over a shiv or other type of contact surface where the line makes a sharp direction change, dyneema can actually be weaker than the same strength nylon line. This is specifically because there is no stretch in dyneema on very small scales such as the distance over a turning block or other object. The effect this has is that the fibers taking the longest route on the outside of the bend will carry all of the load and break first with dyneema. But in nylon or Dacron, the stretch will allow the fibers on the inside of the bend to be loaded and thus not all of the load is taken up by just a few fibers at a time. Another reason that dyneema uses flat braids is to combat this property. Round braids in dyneema running over a turning block or other object would put an extreme load on those outside fibers.

So again the physics are definitely different with respect to dyneema vs. Nylon / Dacron lines.


As for knots, I think it's pretty evident that dyneema knots fail by slow slippage, as opposed to Breaking at the knot or a quick slip of the knot.

So after establishing that the physics are different, I think it is fair to treat dyneema in an knot situation differently than lines that have a large amount of stretch. The elasticity of nylon / Dacron helps with knot retention. The lack of elasticity prevents even some of the most reliable knots from holding in dyneema / Spectra.

I would think that it is fairly obvious that the action of cinching down in a knot is much different then the action wear a splice cinches down on the line inside of it.

Could there be a degree to which the slipperiness of the dyneema surface comes into play? I would think so, but the main culprit of knot slippage in dyneema / Spectra, is that there is no significant stretch with regards to very small scales of length in that material.

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jakemoore
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Re: Munter Hitch QR

Postby jakemoore » Wed Jan 29, 2020 1:06 am

Herman wrote:
Tue Jan 28, 2020 6:57 pm
In my old climbing circles nobody used bowlines because they are notorious for coming loose. ... One of the best things about a bowline is that it is extremely difficult to set them really hard, good for boats - bad for kiting and climbing!
I learned something today so thank you. For kite rigs I've moved exclusively to splicing with a long bury.

I'm curious to see how the Munter release goes because I would also like to ditch the pin.

Herman
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Re: Munter Hitch QR

Postby Herman » Wed Jan 29, 2020 9:55 am

Please don't hold your breath Jakemoore, I had the munter idea at least 5years ago. I mention it now because I am becoming conscious that I am riding around on some old chicken loops that I don't really have much of a clue regarding their life expectancy. It would be nice to move to something that is easy to inspect. Trouble is I prefer riding to engineering!

I will now have a study of Matteo V's input to see if there is anything to learn there.

Regards Herman

Herman
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Re: Munter Hitch QR

Postby Herman » Wed Jan 29, 2020 10:19 am

All good stuff Matteo V but we have a different outlook, which is probably only down to semantics. To me the physics are never different, only the situation is different. The same physics apply to all situations apart from the cat🐈in the box!

PS: This assumes I will not make the event horizon of a black hole!

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Re: Munter Hitch QR

Postby PrfctChaos » Wed Jan 29, 2020 2:17 pm

Herman, what is it that you don't like about a simple pin and ball type release? (like brm style). Seems to achieve the same goals, but a proven design.

Herman
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Re: Munter Hitch QR

Postby Herman » Wed Jan 29, 2020 3:41 pm

Apart from the fact that I have shrink fit but no steel pins the only thing I have against the latch pin is that, because it usually has such a small cross section, it has the potential to do serious damage to a finger or palm if they are in the way during a powered release. If you doubt this just put your finger in the way of the latch pin during a gentle release and you will be in for a surprise. The fact that the munter will have a slower release and is only rope will probably be a benefit in many scenarios.

However to put in perspective I have only seen one latch pin injury in many years of riding but it was nasty, big rip in the palm with damaged tendons and the image has stuck with me. If you are into freestyle powered tricks I would recommend an internal release system. If you rarely release and expect to use the qr in anticipation then latch pin is probably fine?

I don't see it as a major issue just something to be aware of when planning how you release!

PS There is a similar danger with nose release shackles and I used those for years without damaging myself!


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