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Munter Hitch QR

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Herman
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Munter Hitch QR

Postby Herman » Tue Jan 28, 2020 12:08 pm

I am toying with the idea of using a munter hitch, shown below, as a QR. Anybody else doing that?

Would need to source suitable size collar and add a bungee. I would also stiffen the latch pin section with a shrink fit, may splice a loop in it to poke out the collar so it could be locked. Of course I am aware that it has ergonomic disadvantages over click in loops. I would probably use a swivel instead of a ring for slider use.

Even this mock up basically, works.
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IMG_20200128_105006.jpg

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jumptheshark
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Re: Munter Hitch QR

Postby jumptheshark » Tue Jan 28, 2020 12:30 pm

Not sure if I have this correct, but your pin would have to be short enough to pass through the metal ring freely without fear of a hang up on either the ring or the ring/collar combination. The pin would also whip very quickly through its unwinding path when triggered under load. There is potential for hang up if the rider is say on their stomach on the beach, or pulled/pressed against something like their board obstructing the free movement of the pin in all three planes. Long pins that release with force have torn more than a few palms and fingers open potentially keeping you off the water for a bit or worse, and this set up seems to really add to that potential. A short pin would require a decent bungee to avoid unwanted releases. Certainly pretty minimalist in required parts, but you would have to spend a little time really getting the pin length, collar size, bungee and ring size set properly to release perfectly every time. I bet you could make it work, but also don't see the advantage over some of the simple short pin and ball releases that don't require as much wrapped rope path so the pin just has to swing in one discreet plane of movement to fully release. The Board Riding Maui set up has the added benefit of an integrated leash and is simple, compact, easy enough to fabricate, well proven, and integrates with a swivel easily.

Herman
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Re: Munter Hitch QR

Postby Herman » Tue Jan 28, 2020 1:17 pm

Jumptheshark

I think your understanding is pretty much spot on. The size of bail or ring has to be adequate and is also related to the stiffness of shrink fit section. I agree the window of opportunity for a jam is slightly greater. I think it may be possible to design it so that the sting of the whip is taken by the ring, and I hope that it could actually be safer than a steel latch pin. But yet to trial this.

The kites I have this in mind for are top hat center line releases so no flag line to accommodate in the collar but, that is a very good point. It would make the collar more complex if it is to rotate around a flag out line. I feel the only advantages may be cost and in some ways simplicity to make, although I would also hope that the reduction in severity of a latch strike would not be nullified by an increased occurrence. I will trial that with thick gloves on if I take it that far!

Regards Herman.

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Re: Munter Hitch QR

Postby jakemoore » Tue Jan 28, 2020 2:49 pm

Do I understand correctly there is no pin? Just a heat shrink to slightly stiffen the very short bitter end?

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Re: Munter Hitch QR

Postby Herman » Tue Jan 28, 2020 3:02 pm

Yes that is correct, I propose just shrink fit. The mock up in the photo is 50mm masking tape (3 wraps) and it is a very loose fit in the collar and even that works. Probably next step would be to trial a 20 - 30mm shrink fit tail and a ball type collar, could leave extra tail poking out and marked up to see if anything moves. Not for everyone tastes of course!

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jumptheshark
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Re: Munter Hitch QR

Postby jumptheshark » Tue Jan 28, 2020 3:18 pm

How much of the munter hitch is friction or rope on rope binding dependant? Pure dynema is pretty slippery and binds poorly. A simple overhand knot is usually not enough for a pigtail ends as they can be "pushed" or slid out under loads like a larkshead. Usually takes a fig 8 to properly end dyneema pigtails and even then I either melt the end into a large enough blob or leave a long enough sleeved (tape) tail. You might end up with some residual push on whatever sleeving you use to terminate your line. Which could mean you run into grip issues between rope and heatshrink that would not really impact climbing rope the same way due to the far better binding friction. If I understand the munter hitch is also meant to be a belay option, so is designed to slide when you want it to.

These "grip" issues may also be influenced by the fact that the rope will be wet.

may not be a problem as you already have a mock up that looks like it may work under load, just brainstorming potential issues.

To my thinking this release requires the "pin" to travel through the ring twice as well as around the depower line once, where with other kite pin and collar releases the pin only passes through the ring once.

Be sure to test it well.

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jakemoore
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Re: Munter Hitch QR

Postby jakemoore » Tue Jan 28, 2020 3:27 pm

I have had a bowline pull out through amsteel. Now I put an overhand knot in the bitter end of another knot to keep it pulling through.

Maybe a less slippery line.

Herman
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Re: Munter Hitch QR

Postby Herman » Tue Jan 28, 2020 4:48 pm

Lots.of good points raised and they are largely why I asked if anyone had done it. Imho if dyneema was too slippery for a munter it would be too slippery to splice. Tie one for yourself and hold the bitter end parallel to the standing part and you will feel that virtually no load reaches the tail, a latch pin is more loaded imho.

Bowline will flog out of any rope I have encountered and so I do not regard them as good indicator of slipperyness. However I do think that is an example of what may be the biggest drawback. I would expect the munter to work well under load but any unloaded flogging may cause it to loosen and maybe creep on next tightening.

It will probably work ok but will need some care and attention like a climbing knot and would not be good for all.

If I trial it properly I will post the results. Thanks for all the comments.

Regards Herman

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Re: Munter Hitch QR

Postby Matteo V » Tue Jan 28, 2020 5:19 pm

Herman wrote:
Tue Jan 28, 2020 4:48 pm
Imho if dyneema was too slippery for a munter it would be too slippery to splice.
So for your buried length in a splice on dyneema / Spectra, is it a good idea to add extra length versus nylon / Dacron? Or is this unnecessary?

Also, I have a hunch that a knot has somewhat different physics at work compared to a splice. Doesn't a splice add more friction as the load increases? But a knot does not necessarily add more friction as the load increases in the same way. Essentially spices and knots are two different animals, are they not?

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Re: Munter Hitch QR

Postby jakemoore » Tue Jan 28, 2020 5:30 pm

In the case of the bowline it was not a loose flogging line but rather kite bar centerline on an old Flysurfer in the days of of the rotoleash and 17m Speed 1. I swapped the CL for a Wichard IIRC. The bowline felt tight and perfect on the beach but slowly slipped out while riding under twin tip forces in light winds. The rotoleash clip subsequently broke off my harness and I had a bit of a swim.


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