Dyneema slings and loops

Make your own gear? Talk about it here!

Moderators: Bearbonesnorm, Taylor, Chew

Post Reply
User avatar
whitestone
Posts: 5921
Joined: Thu Dec 04, 2014 10:20 am
Location: Skipton(ish)
Contact:

Dyneema slings and loops

Post by whitestone » Sat Jun 06, 2020 3:03 pm

I got some Amsteel cord the other day. Basically it's a single braided kevlar/dynema rope or cord. Just 2.5mm diameter it has a breaking strength of around 800kg. The big problem with it is it is very slippery and knots tend not (sic) to work very well as they come loose with alarming ease :shock: The solution is a technique called a "Locked Brummel" along with a bury or constriction similar to those paper chinese finger traps you might have played with as a kid.

So I followed a few online tutorials but bodged the tools - I used a pencil for the awl, a safety pin to unpick parts of the cord and some plastic coated garden wire for the threading tool! It's quite an easy technique and once you've done a couple it's simple to knock up another loop or sling.

In the shot below from top to bottom you have a continuous loop, a dog bone and a whoopie sling. Centre bottom on the latter you can see the constriction where one part of the line has been threaded through the inside of another part. The two washers are there as a "stop" to prevent the adjustable loop being pulled through the constriction. Slightly harder to see at the other end of the constriction is a tail where the cord has been turned in on itself, thus increasing the diameter, for the same purpose.

Image

The whoopie sling is made from 12'6" of cord and weighs just 15g, the loop and dog bone are about 5g each.
Better weight than wisdom, a traveller cannot carry

Taylor
Posts: 3137
Joined: Sat Jun 18, 2011 9:27 pm
Location: Brizzle
Contact:

Re: Dyneema slings and loops

Post by Taylor » Sat Jun 06, 2020 3:36 pm

He's got the hammock bug.

User avatar
whitestone
Posts: 5921
Joined: Thu Dec 04, 2014 10:20 am
Location: Skipton(ish)
Contact:

Re: Dyneema slings and loops

Post by whitestone » Sat Jun 06, 2020 3:38 pm

Taylor wrote:
Sat Jun 06, 2020 3:36 pm
He's got the hammock bug.
:lol:

Someone :???: has commandeered mine :roll: Got some material on the way to make another.
Better weight than wisdom, a traveller cannot carry

User avatar
sean_iow
Posts: 2601
Joined: Tue Sep 30, 2014 12:08 pm
Location: Isle of Wight

Re: Dyneema slings and loops

Post by sean_iow » Sat Jun 06, 2020 3:50 pm

That's exactly the same technique we used to use with dyneema winch lines on land rovers.

I was skeptical when I first saw a loop formed by threading back through itself but having seen a loaded 110 land rover winch itself out of a door bottom deep mud hole I changed my mind.

It's much better than trying knots, the harder you pull the stronger the join. The lines were originally developed for traulers as when the do snap they just drop to the floor instead of flying about causing injury, a trait also handy for off roading. I guess your hammock lines are just a miniature version, ours were 10 to 12mm dia.
Adventure without risk is Disneyland - Bikemonger

Cheeky Monkey
Posts: 2438
Joined: Mon Aug 01, 2011 1:48 pm
Location: Leeds ish
Contact:

Re: Dyneema slings and loops

Post by Cheeky Monkey » Sat Jun 06, 2020 4:17 pm

Amsteel and other dyneema lines are amazing stuff, incredibly strong and light.

As you say it doesn't hold a knot at all well and they substantially weaken the cord so hammockers have been using splicing techniques for a while.

I bought one set of whoopi slings but after reading up a little bit and seeing how easy they were to make I've always made my own since. The guyline set up I use is one from a hammock forum that allows you to tension from inside the shelter as well. It's one small continuous loop for a prusik and a longer "guy" which has a closed loop one end to peg and a bury at the other.

Try a soft shackle. They're pretty handy and getting the "button" knot was quite satisfying. Also, try plastic beads instead of washers, if you fancy.

I use a Ti peg to open the line (on narrow gauge stuff) and a combo of plastic and metal darning needless from Hobby Craft. Wire is easier on larger gauge for whoopies.

Just watch out for Ti fasteners and Dutchgear. Another slippery slope!
Last edited by Cheeky Monkey on Mon Jun 08, 2020 10:09 am, edited 2 times in total.

User avatar
whitestone
Posts: 5921
Joined: Thu Dec 04, 2014 10:20 am
Location: Skipton(ish)
Contact:

Re: Dyneema slings and loops

Post by whitestone » Sat Jun 06, 2020 5:00 pm

I remember when dyneema came out in the 1980s and it began to be used in climbing cord. That was kernmantle rather than braided. A right pain to work with!

Whoopie slings sound complicated but having made two I reckon I wouldn't need to refer to instructions again should I need to make another, dead easy. The first Whoopie sling I made has a plastic bead/washer but that was the only one I could find so I used some cup washers for that one.

Soft shackle is next. I've been looking at tutorials from a Youtube channel called Tacblades, nice and clearly done, his version of the soft shackle uses a closed loop overhand knot that apparently won't roll like the diamond knot can.
Better weight than wisdom, a traveller cannot carry

Cheeky Monkey
Posts: 2438
Joined: Mon Aug 01, 2011 1:48 pm
Location: Leeds ish
Contact:

Re: Dyneema slings and loops

Post by Cheeky Monkey » Sat Jun 06, 2020 6:55 pm

Most of the stuff I learnt was on hammockforum. Nerd to the nth degree 😉

User avatar
BigdummySteve
Posts: 2278
Joined: Sun Nov 20, 2016 9:16 pm
Location: Oxfordshire

Re: Dyneema slings and loops

Post by BigdummySteve » Sat Jun 06, 2020 6:57 pm

We started using dyneema soft shackles to attach parachute canopies to the risers, on high performance canopies you collapse the slider and pull it down over the risers tucking it behind your head to minimise drag, initially some riggers were reluctant to replace the steel connectors until the manufacturer showed a drop test where the harness failed before the dyneema! At which point the skydiver would have already died due to the shock load anyway...

Later performance canopies used them for suspension lines, again reducing drag.
However they were banned for CREW ( docking canopies etc) as the lines were like cheese cutters, both to kit and bodies during entanglements.
‘ it’s good to be lost, I don’t want to be found’ -HMHB

User avatar
whitestone
Posts: 5921
Joined: Thu Dec 04, 2014 10:20 am
Location: Skipton(ish)
Contact:

Re: Dyneema slings and loops

Post by whitestone » Sun Jun 21, 2020 12:23 pm

Further playing about ...

Turns out the "improved" soft shackle is straightforward. Did one about ten days ago and another this morning, the second one took all of fifteen minutes. I find the hardest bit is creating the taper, it seems really awkward picking out the strands.

I'd been concerned about directly larks footing two amsteel loops together and then someone suggested an "EVO loop" (not sure if the capitalisation is correct), with "evo" being short for "evolved" or "evolution". These are basically the standard continuous loop as seen at the top of the shot in my first post but with a button knot at one end. The trouble was, all the YouTube videos showed you how to use them not make them. Then I had a lightbulb moment, they were basically the soft shackle but without the slip loop at the opposite end to the knot. All that I needed to work out was the length of cord to start with. After a couple of false starts I settled on 40" which gave me an 8" loop with a secure knot at one end.

They work by pushing a bight of a normal loop up through the evo then back over the knot and cinching it down. They rely on continuous weight/pressure being applied so no good in dynamic situations. In the shot below, the evo loop is black and the standard loop is blue. The red prusik is something I was looking at as extra locking to prevent any movement but i don't think it's needed.

Image
Better weight than wisdom, a traveller cannot carry

Post Reply