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dyneema rope

stig

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I was ordering some 12 mm Dyneema today to use for pulling trees, it has a breaking strength of 16 tons.
I was told by the manufacturer that the strength is greatly affected by knotting the rope, they could not, however tell me by what factor.
It is a newly started busines that makes rope and slings for the fishing industries.
They have no experience in the use of ropes in tree work, I just figured 16 tons is 16 tons whether you tie it to a seine net or to a tree.
Do anyone here have any experience with it. It is the same product as Spectra, just a different trade name.
 

lumberjack

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It's strength will be reduced significantly. To the point where most would find it to be more effective to just order a poly rope.

For pulling trees you can run it over a limb, down to the base of the tree, and have a spliced eye and a shackle to terminate that end. A porta wrap on whatever you're pulling with would handle that end.

You could use a couple round turns around the spar and terminate it with a bowline.

It won't like having a bowline or any other tight bend under a high loading. The round turns act like wraps on the porty, taking most of the weight off the knot.

Normally on the bottom of the trunk I'll make a wrap or two before I put the shackle on.
 

stig

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Thanks, I was wondering if the strength reduction is bigger than the 50% that one more or less counts on when knotting other ropes.
I'll write the manufacturer and asked them to put an eye splice in both ends.
 
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B

Bounce

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What Carl said. x2

the sharper the bend radius caused by the knot, the greater the breaking strength loss. This is why they splice the terminations instead of tying knots when they use this stuff on fishing boats. I saw some results of testing done by Samson on Amsteel Blue that showed 50-90% strength loss depending on which knot was tied.

Almost as bad the as knot problem is the poor abrasion and heat resistance. If you use this with a port-a-wrap, be prepared for it to break. Melting point of dyneema/spectra is LOW! The loose braid allows strands to be plucked easily as well, so make sure to use pulleys to eliminate abrasion.
 

lumberjack

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Just to clarify, I was saying use a porty to have a midline connection point on the rope, not for lowering with.

The only knot I know of off hand that has a 50% reduction in poly would be an overhand knot. A bowline still retains around 70% (30% reduction).
 

NickfromWI

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Yes, a strength reduction of 50% is VERY common in these types of ropes. They will sometimes just slip right open when pushed to the limits.

Yes, spectra = dyneema = ultra high molecular weight polyethylene

Splice it. Add a thimble. Put a steel snap on the end if you want to avoid the knot.

love
nick
 

stig

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Thanks guys!
The idea of using a porta wrap as connection point between the end of my winch wire and the dyneema rope is great, I hadn't thought of doing that.
This is not a rope that'll get a whole lot of use, I just wanted it for those trees where using hard rigging for pulling would be like shooting sparrows with a cannon, as we say here.
Since we normally place it with a throwline and bigshot, I figured the light weight would make life easier for us.
 

stig

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A porta wrap on whatever you're pulling with would handle that end.

.
Carl, I owe you a big thank you for that tip!

I have done it everytime I use the dyneema rope for pulling, and it works really well. Impresses the heck out of everybody who sees it, too.
Then I tell them I learned it from an american, and that impresses them even more, most danish fallers are VERY local guys.
 
B

Blinky

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Yep, Black widow is regular Amsteel. Got that from Samson direct. Spliced eyes are the way to go with that stuff.
 
K

knudeNoggin

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Yes, a strength reduction of 50% is VERY common in these types of ropes. They will sometimes just slip right open when pushed to the limits.

Yes, spectra = dyneema = ultra high molecular weight polyethylene
Well, 50% is quite UNcommon(ly HIGH): in testing for using Amsteel as a
replacement for wire rope in forestry applications (because it's MUCH easier
to handle--weight, *splinters*, ...), a university study found it failing in the
Bowline at 20%?, by slipping out; when secured with a stopper in the
end, the bowline broke at 33% or so. This roughly matches testing done
by Brion Toss (or with his initiative & consultation/involvement) as reported
in SAIL mag. 2001(?)-Sep(?).

Sadly, though, no good efforts to work around this demonstrated weakness
were tested; e.g., to repeat--back'n'forth--the "rabbit-goes-around-tree-&
-back-through-the-hole" maneuver to stuff 3-4(-5) diameters through that
critical area vs. the usual two. But I'll guess that at best that might bump
strength only up to the 50% zone (which, after all, would be a 2/3 gain!).
(Or, tying the bowline with a bight/doubled-end , which will put four
diameters through the hole. But there might be some aspect of heat
build-up, regardless, that will weaken this heat-sensitive material.)

Yes, the PortaWrap idea's a winner!

*kN*
 
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