Lightweight 3,000 lbs breaking strenght webbing ?

[Rouskof]

If I use cordage, I am hesitating between these two :


1) 6 mm pure 12-strand Vectran rope, rated at 8,000 lbs tensile strenght, or
2) 6 mm polyester covered Dyneema rope, like the WarpSpeed® II Dyneema® Double Braid, rated at 5,100 lbs average strenght.

6mm pure Vectran is stronger, but I have read these new low stretch materials can loose a lot of their strenght in knots (up to 70% apparently), so I was thinking maybe a less strong Vectran core with a polyester cover might be stronger in the end than a thicker bare Vectran.

I am not too worried about friction, as I think I will use aluminium rings in the loops when tensioning the rope, but about the knot itself, that, even though it will hold, might weaken the strenght of the rope.

What is your opinion ?

(The 6mm pure Vectran would be 2.7 grams per foot heavier.)



On the other hand, a 5mm pure Vectran is rated at 4,500 lbs tensile strenght, and it would save me about half the weight (it weights only 5,4 g/foot compared to the 10g/foot of the 6mm pure Vectran). Considering I will have about 60' of cordage, that means a significant 276g weight saving. Do you think the 5mm pure Vectran would be strong enough for this application ?

Of course, there is not scientific basis in this guess, but I am still happy to have several opinions.

Thank you.

[Rouskof]

There might be some rescue services that have higher dyneema than Dutch.

I found this dyneema strap : http://www.bainbridgeint.com/Item.as...artNo=E135SPBK

7,3 g / foot
breaking load : 6200 lbs

Seems ideal ? The problem : it is almost more expensive than the tent.

[gmcttr]

Bare amsteel, vectran and similar ropes are terrible choices for use with knots. They are designed to be spliced. Knots typically reduce tensile strength (breaking strength) to (not by) 35% of the rated strength. Thus, an 8000 lbs rated rope might fail at 2800 lbs at the knot.

The polyester covers on these types of rope not only improve friction within the knot, but more importantly, increase the bend radiuses within a knot and therefore knots do not derate the strength as severely. The covered ropes may only be derated to 50-75% of their rated strength (if memory serves me correctly). However, if the cover fails, the slick core fibers may simply pull through cover at the knot and still leave you headed for the ground.

Do your research before selecting components for high stress applications.

[Phantom Grappler]

Friction knots--slip and grip knots might burn or melt rope under high stress. Knots that you use to tie off at rings will have to be tested for grip and resistance to being crushed. You might be able to test short lengths of cords before buying a couple hundred feet.
And if you have a hollow braid rope that can be spliced--you might consider a UCR (utility constrictor rope) with Not a minimal bury, but a Really Long Bury. Since you want to cover longer spans--you will have plenty of room for long buries.
Also I was working on splicing a UCR for hammock with 1/8 amsteel as the sheath and a different fatter more grainy rope as bury. It was hard to splice, as inner rope was larger diameter than outer rope.
It had incredible gripping power.
I abandoned this idea for hammock camping due to excess bulk and weight.
With a long bury ( use charts and formulas to figure minimum bury length, for size rope used) and double it or more--that combined with a fatter more grainy spyderline core will hold like there is no tomorrow.

Spyderline or something like it--the inner part of bury does not need to be hollow---but if it was hollow and still larger than outer sheath--then you can splice it for end loops and other splices.
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[Rouskof]

I am not familiar with ucrs, but can they be adjusted loaded, because in this case, there is a tent to lift up in the air !?
@gmcttr: thank you for the sound recommendations. I will use a covered dyneema if I am to use rope, but from what I understand, even this is hazardous, so my understanding is the dyneema strap is the way to go if I want to safeguard the advertised breaking strength of the webbing? Maybe a 3000lb rated dyneema strap would be enough in this case?

[Phantom Grappler]

The more I think of it, the more I think UCR is the way to go. UCR with Long buries. And possibly UCR with Long bury, combined with having the inner bury slightly thicker than sheath, and possibly combined with inner bury made of a rougher more grainy rope like spyderline.
Or maybe UCR with amsteel both lines the same---still with a Long bury.
This could give rapid setup if you had carabiners or quick link chain links to hook one end to flying tent and other end to tree. Then all you gotta do is pull it tight.
Good luck Rouskof!
Post pictures or a video if it flys!


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[Rouskof]

Then all you gotta do is pull it tight.

You wouldn't get enough tension just by pulling. They normally use a ratchet. Watch their set up video. That is why I was thinking of the Trucker's hitch.

[Phantom Grappler]

I did not think you needed suspension spang tight. I do not know if this would apply--a hammock hang of flatter than 30 degrees but not flat can give a really tight hammock ridgeline. Maybe this would not carry over to a flying tent.
If using a truckers hitch, I would use two alpine butterfly loops. And no rings. End of rope would go through ABLoop and pull tight, then back to other loop, pass through and pull tight, then back to first loop and when passing rope through---pass rope through loop in opposite direction of original pass through this will help keep tension while applying secure knots.
I borrowed this idea of passing rope through loop in opposite directions from two knots that do the same: zeppelin bend and a simple-hitch-a-la -gleipnir.

Alpine butterfly loops would have a strong smooth toggle placed into interior of knot before tightening. When untie knot use a wooden mallet to tap toggle out of knot, now it is easy to untie.

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[Rouskof]

So you want me to carry a wooden mallet on top of all that ? ;-)
Thanks for the advises, I wouldn't have thought of passing the rope in opposite directions. The whole process seems really fun, I am looking forward to it !

Tentsile setup video: https://youtu.be/zgSGPMAEO0M

[Phantom Grappler]

A smooth stone can be used for mallet with t-shirt sock or paper towel in between to protect rope. And if a toggle ever slips out of knot by accident--the alpine butterfly loop will keep on trucking and maybe tighten amount taken by toggle.


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