knots in dyneema, what's the strength ?

[Clarky]

Some knots dont work that well with dyneema,I noticed that some of my climbing equipment had triple fishermans as a normal double would slip,according to the climbing shop.

 

[bbg]

Some knots dont work that well with dyneema,I noticed that some of my climbing equipment had triple fishermans as a normal double would slip,according to the climbing shop.

Surely dyneema isn't used in climbing? Or is it only for very specific applications? I struggle to think of an application in which you would need dyneema, in climbing.

 

[Woodlouse]

Surely dyneema isn't used in climbing? Or is it only for very specific applications? I struggle to think of an application in which you would need dyneema, in climbing.

It's very resistant to chafe so I'm not all that surprised. I bet falling off hurts though when it brings you to a stop.

 

[ropeworkuk]

Hi Simonfraser,

Go for a locked brummel in possible (fittings spliced on to the one end are small enough to pass through braid).

Or you could do a mobius brummel

Both better than an open brummel

There is a cool website "the house of splice" full of detailed HPME splicing

Or you can contact me

Cheers

 

[lw395]

The thing with dyneema is that you have to buy it far thicker than you actually need simply so you can hold it. I have 10mm Dyneema main halyard on my boat simply so that the clutch can grip it. Even then when it blows we have to keep the halyard on the winch just to stop it slipping through the clutch.
When I went to the chandlers to buy the halyard there was a man from the manufacturers there showing people how to splice multibraid rope. He offered to put a splice in it for me so I said gop on then. After an hour and two very bent fids he gave up and said tie a knot in it.
When it comes to strength you really can get away with much thinner than you think. Earlier this season I sailed on a Dragon which was fitted with 3mm dyneema backstay and runners. The ends were spliced on them. No idea how they did it though. I suppose they had to justify the enormous price somehow.

Thin dyneema core is very easy to splice, you just use a hollow needle to put the end inside the standing part through a gap in the braid. Doing a neat splice with covered dyneema is harder.
If your halyard slips in the clutch, the only real answer is to sleeve the areas where the clutch works with the outer braid from a polyester rope. Or you could have a soft eye in the dyneema part of the halyard, then attach a tackle to it to tension it when the main is raised. That's roughly what we do on a keel boat. It means only the tensioned part is dyneema so you only have to buy half as much. The tail to pull it up can be anything that's easy to grip.
One of my dinghies has a 4mm dyneema halyard, rigged as a 2:1. This fails at the knot if you don't remember to chop 2 inches off and move the knot every couple of months. The halyard goes through a hole at the top of the mast and is secured by a figure-8 knot, so I suppose the rope is point loaded, but it would not trouble an old style polyester rope. But it does not fail quickly, even if you put much more tension on it. In contrast, splice kicker tackles seem to last indefinitely.

I'm not sure if this is the whole story, but I think the trouble with knotting/kinking these ropes is that it puts all the load onto a few strands that run on the outside of the bend, whereas in a poly rope, the highest loaded strands would stretch sharing the load with other strands, in a high tech rope they break and then the next few strands take the load.
Probably not the whole story.

 

[Iain C]

If you want to see a heavily loaded bowsprit try this! That's me helming the 12' Skiff Harken/DesignSource. However the whole lot would collapse without the dolphin striker and 2 sets of spreaders. That's the number 2 rig...there is a bigger no1 for light airs with a triple spreader mast and a 60sqm kite...on a 45kg boat!

I love the new styles of materials (dyneema/vectran/V12) and they will take a ludicrous amount of load, but make sure it's spliced properly, NEVER KNOTTED, and with the correct hard eye where appropriate. There's a common misconception that it's "long bit through short bit" when splicing...wrong...it's short through long and then long through short if that makes sense...and make sure you taper the end of the bit that you will "loose" inside the string itself.

I also sail 18s and we have all three crew dangling off one bit of string up the rig...and of course all trap lines are string too for lightness and safety (you can cut them if the poo hits the fan).

Invest in a set of decent fids and enjoy!

 

[PerformanceSailor]

Knot much to disagree with...

Apropos of high tech line in general... when we replaced all four of our original wire-to-rope halyards about ten years ago on our '88 boat, I went with T-900, which was/is a garden-variety modern line. This is a New England Rope product, described as a "Unique braided Spectra/Technora core with a braided polyester cover."
I used 5/16" because that would best fit the mast head sheaves and also (barely) hold in our clutch stoppers.

I fretted a bit about the whole knot vs strength issue, and finally realized that the line was rated at 7000# break strength, approx the same as the ss shrouds that hold up our mast!
If my lowly knot reduces the strength by 56% or 37.2% or whatever, it just really makes no practical difference for the application, i.e. a halyard.
I have been using an "anchor hitch" at the snap shackle end.

My experiences only, with no guarantees.

L

 

[Bobobolinsky]

I never find thin dyneema to look convincing, I think they use bare 2.5mm for trapeze lines, i.e. just replace the wire size for size. You expect me to hang out on that? Doesn't seem reasonable...

I think just looking at dyneema in a funny way takes several % off its breaking strain.
I love the stuff for dinghy use, it's so easy to splice and replaces wire in kickers etc wonderfully. But unless there is overwhelming reason, I don't want to go near it's alleged breaking strain. When 5mm dyneema goes around pulleys better than 2mm wire, why scrimp on it?

Come on have you not seen Mr J Bond using his shoe laces.

I've used thin prussics, typically 4mm, and I am not a little guy.

I reckon the 56% strength reduction is pretty close for a singled knot. A figure of eight or nine gives about a 20% reduction.
Wet ropes of the core and sheath construction, also have a reduction in strength, though I have never seen any figures for this

 

[dam747iam]

knots

for a knot that is very strong use a palomar knot used in fishing for braided lines, trouble is you wont undo it

 

[Clarky]

Surely dyneema isn't used in climbing? Or is it only for very specific applications? I struggle to think of an application in which you would need dyneema, in climbing.

Its used to thread camming devices and other pieces of hardware placed in rock for protection.The shock loads in falling situations are enormous,imagine 120 m ,large male freefall , hence the use of dyneema ,and the problem of securely knotting it.