Dyneena???

[Ian_Edwards]

Is there any quick way of telling if a rope is Dyneema?

I have two lengths which came with my new to me boat, which I don't need and which I'd like to sell. I think that they are Dyneema, but I'd like to be sure before I put them up for sale.

 

[lw395]

The way the core melts with a lighter on the end is distinctive.
Hard to describe, but it sort of shrivels rather than melt like polyester.
Or apply a load and measure the stretch.

Also the coloured marker threads identify the manufacturer and type of rope (in many cases).

 

[William_H]

I had some really cheap rope from local hardware chain from China. I clamped one end in the bench vice and took the other end outside to the end of 20 metres of the rope. When I pulled on it it stretched to an amazing degree. So if you have similar length of known polyester braided rope you could compare the stretch that you can achieve with that of your possibly dyneema rope. You should find a dramatic reduction in stretch with the dyneema. good luck olewill

 

[cryan]

Dyneema has virtually no stretch. It floats and it is lightweight. Its also very expensive compared to nylon/polyprop etc, so much so that if your rope was dyneema I would have thought the seller would have highlighted it as a selling point.

 

[Ian_Edwards]

Cryan, the reason I want to know is because I want to sell the rope, if I'm sure it's dyneema, I'll put a higher asking price on it!

 

[Neeves]

If you can stretch it, its not Dyneema. I assume you must have a decent length (or its not worth the aggro) so tie it to a tree, tie the other end to your car, or even better someone elses. If it stretches etc. Though even Dyneema stretches a bit first off if its new, but once its been through the pre stretch it should be like steel. Nylon etc stretches and stretches. But if you follow thes einstructions, you might find you need a vice to undo the knots.

Take care and good luck.

Jonathan

 

[macd]

But if you follow thes einstructions, you might find you need a vice to undo the knots.

Luckily he has a vice, although his wife perhaps calls it "sailing".

 

[AndyJ76]

The Dyneema core has a heat absorbing characteristic, so if you remove some of the core (as if you were doing an eye splice) and hold it in your hand, it will feel cold.

 

[lw395]

The best way is to measure the stretch.
Estimate the breaking strain from a similar size and construction of dyneema rope.
Once you have taken out the slack, it should stretch about 2% to breaking strain, so measure out 10m, load it to say 5% of break, mark the length, then double the load.
If it only stretches 5% x 2% x 10m = 1cm, it's probably dyneema, unless its core is a yellow colour, in which case it's Kevlar.

I did this with a 12metre length of 3mm 12 braid, from the balcony of a tall building, putting my weight on it. breaking strain should be about 1 ton, it stretched about 5 cm when I put 10kg on it (the first amount is a lot as the strands settle), then only a further few cm with my weight.
This also proved my splices work!
That 12m length was a small part of a £5 bargain hank!

 

[Ian_Edwards]

I have 2 lengths, 20m of 14mm and 25m of 12mm. The breaking strain of these is over 6tons for the 12mm and over 9tons for the 14mm, so I don't see stretching the rope as a realistic option.

I'm now confident enough to advertise it as dyneema based on the melting characteristics. The outer braid melts as you'd expect, the inner core doesn't really melt and fuse, it sort of shrivels and doesn't fuse together well.

the 12mm looks like D2 Competition 78

http://www.marlowropes.com/leisure-marine-products-1/cruising-racing/d2-racing-75.html

and I haven't yet identified the 14mm the braid cover is white with 2 blue strands which form an X pattern

Thanks for all the useful suggestions.