Best knot for dyneema tape

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 Green Porridge 11 Dec 2022

For my birthday this year I received a hammock. As one does, I tested it out using a couple of trees in the garden. The trees are a bit far apart for the hanging straps though, so I extended them with some old dyneema slings - so far so good. 

It got me thinking that it might be good to take a couple of slings with me if I'm taking the hammock with me when travelling, but I'd like to save some weight and bulk. I was thinking about cutting the old sling open, and making a loop at each end thus more-or-less doubling the length, and halving the number I would need to carry. What would be the best easy to do this? Overhand knot? Water knot? Trying to home-brew some bar-tacks on my wife's sewing machine would be ideal, but I dont know how feasible this is. Safety is not a huge worry, as it will be a static load, slowly applied, with a maximum ground fall potential of about 0.3m to 0.5m. The sling itself is about 15 years old, so this would feel like a worthy retirement for it. 

 Tintin 11 Dec 2022
In reply to Green Porridge:

I'd go with a simple larkshead or marlin spike hitch.

 CantClimbTom 11 Dec 2022
In reply to Green Porridge:

If you can't simply melt the ends like nylon, when you cut your sling to do this, what'll stop the frayed end progressively coming more and more ragged?

In reply to CantClimbTom:

Oh,  I'd melt the ends, regardless of what method I go for. 

In reply to Tintin:

I don't think either of those achieve what I'm trying to do. Essentially, I would have a long bit of tape, and I want to put a loop in each end. A bit like trying in to the end of a rope where I would use a figure of 8 or a bowline.

 CantClimbTom 11 Dec 2022
In reply to Green Porridge:

Yes, but dyneema (and equivalents) don't melt helpfully, not like nylon anyway

1
 steveshaking 11 Dec 2022
In reply to Green Porridge:

Dyneema has a lower melting point, ~145°C, compared to Nylon (245°C). Possibly you were thinking of Aramid.

But I've never done it. So how usefully it melts I don't know. As a sailing site says:

 use a thin cyanoacrylate glue to stiffen the line where it is to be cut and use a sharp cutting knife (we use snap off blades to ensure a sharp edge) on a cutting mat to make a clean cut at an acute angle to the line.

Knots:

youtube.com/watch?v=b9GLp1Esins&

In reply to CantClimbTom:

That's good info, thanks. If the worst comes to the worst I can just wrap the fraying end in tape or heat shrink or something. Or try to heat a knife to seal it. It doesn't really matter if it's a couple of cm shorter with time.

 PaulJepson 11 Dec 2022
In reply to steveshaking:

Dyneema doesn't melt in a helpful way where it glues itself together like nylon does. 

 Holdtickler 11 Dec 2022
In reply to Green Porridge:

For the hammock ends, an overhand would be fine to create a loop that you can clip the hammock to, or a fig 8 if you want slightly more chance of ever untying again. I'd leave the tree ends free of knots and good and long to leave you options. You want to make sure you use releasable knots (but secure obviously) to attach to the trees if you ever want to move it again as the vector forces will totally jam other knots. 

The thing to watch out for is any rub point where you rig it as the gentle swaying of the hammock can eventually saw through. This can be bad news if there happens to be a large plant pot underneath for you to knock yourself out on. Learn from my mistake

1
 Hooo 11 Dec 2022
In reply to Green Porridge:

I've done exactly this with the hammock I made during lockdown. It was too bouncy rigged with static rope, so I found a damaged dyneema sling, cut it, and tied a loop with an overhand in each end. Given the low load, I didn't think any more deeply about what knot to use. It's been fine.

 oldie 11 Dec 2022
In reply to Hooo:

As it's been fine the simple solution answers the OPs question. I suppose if someone was still worried about slippage two overhands in series would do. Also I wonder if an adhesive inside the knot while it was being tied would be useful.

 Hooo 11 Dec 2022
In reply to oldie:

It really is such a low load that you don't need to think about how to tie the best knot, anything will do. When we talk about knots in dyneema slipping, we are talking about loads several orders of magnitude above what you will experience rigging a hammock.

It's definitely worth using dyneema though. The strength is not important, but the lack of stretch is.

Post edited at 11:01
In reply to Green Porridge:

Thanks everyone - much appreciated. Seems like I don't need to think about it too much, and the biggest difficulty looks like it will be sealing the cut ends of the sling. Cheers! 

 Martin Hore 11 Dec 2022
In reply to Green Porridge:

I don't think you said how long the slings currently are. You might find that by the time you've tied the knots and left a tail on each one you don't end up with anything much longer than the original sling..

Martin

 Holdtickler 11 Dec 2022
In reply to Green Porridge:

The way we sometimes daisy chain the top ropes down the wall (bight through a bight through a bight through a bight, repeat n times...) is a nifty finish to make it releasable. Tuck the tail through the last bight to stop your mates from pranking you and tugging the quick release!  

In reply to Martin Hore:

Yes, good point. They're currently 120cm, so the gains aren't huge, but I don't really need them to be. They are also the most knackered slings which I'm most willing to chop up (and probably should retire). The hammock itself is finished at the ends with a small loop of cord, and a wire gate carabiner rated to 12kN I think (so not for climbing). I also have pair of hanging cords for it which are basically about 150cm of I guess 5mm accessory cord, with a nifty aluminium toggle in it to provide friction and allow you to adjust the effective length. There is a bowline in one end of each cord. The idea from the manufacturer it's that you girth hitch a tree with the cord, and use the toggle to adjust the length and therefore tension on the hammock. The problem I have is that the two trees I can use are a bit too far apart and a bit too 'girthy' to be able to just loop these hanging cords around them and crack on. I linked two 120cm songs around the tree with a crab which left plenty of surplus then connected the hanging cord to the crabs. This meant I went from having not quite long enough cords to plenty of excess. I just wanted try and do this with a single sling on each tree, rather than with two. The fact that I don't have to loop the hanging cords around the trees wins me a lot of flexibility. 

1
In reply to Green Porridge:

Quick update: I tried it with my oldest 120 cm sling. The comments about the knots taking up quite a bit of tape were well founded - with an overhand knot in each end, I've got an effective length of about 160cm.

What surprised me most was the method of sealing the ends. I dabbed super glue on both sides of the sling over a length of about 8 mm, waited about 5 minutes for it all to dry and then cut with a sharp knife. The results were really very good - a nice, crisp cut which gives every appearance of having been cut with a hot knife, and doesn't look like it will be fraying any time soon. A method to recommend, at least for low-stakes applications like this. Thanks to all who provided suggestions! 

Edit: typos

Post edited at 14:12
 jkarran 12 Dec 2022
In reply to CantClimbTom:

> Yes, but dyneema (and equivalents) don't melt helpfully, not like nylon anyway

But they're hot cut from the factory?

OP: I'd form a small double fig8 one end of the tape, pass that around the tree, thread the tail through the loop and snug it down (like a larksfoot) so it grips the tree. Clove hitch the hammock end onto a krab, back it up with a knot which isn't normally loaded. Loaded knots in thin tape quickly become permanent and hammocks impose a lot of load.

Assuming it's a furry old 12mm dyneema-nylon mix it shouldn't slip.

jk


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