The truth about dynaglide and safety...

[opie]

Something to think about....

A section of line can not be tested unless its been spliced. There needs to be eyes on the ends to attach to the test bed. Samson states their ratings are for spliced line.

A 10% derate over manufacturer numbers is a good idea in theory for spliced line, but the numbers generated were done on spliced line.

[jwright]

FWIW -
I trust my splices and whoopie constrictor far more than I trust the tight bend of the larks head where my whoopie attaches to my tree straps. That tightens down to a pretty small radius.
I hang without fear (ignorance may be bliss) but do visually inspect my suspension up as it is going up.
Jason

[Dead Man]

I gotta say in reading through the total of this thread that you guys have put the fear of God in this noob.

As one who is about to DIY his own hammock and woopies using 7/64 amsteel for the woopies (I know - you're talking about Dynaglide), I will likely make the buries a tad longer than everyone else and be a nervous nelly when checking the suspension and getting in the hammock each time I use it.

But isn't that the point of this whole exercise in a nut shell (no pun intended)? We all make "personal" choices about what equipment we use, where we use it and how we use it. In the end, the responsibility of the user is to mitigate risk to a level he/she is comfortable with.

I've been reading, watching videos and more reading for months on woopies and hammock making, before I would even tentatively pull the trigger on supplies to make my own. Limits will always be pushed, math (good, bad and ugly) will be put out and decisions will be made on that and a miriad of other factors. In the end, faith, faith in your product, your suspension, your math or your experience will dictate a choice that you are willing to live with (or die with as some have put it ).

I wouldn't want anyone to get hurt from the choices I proport nor would I take what others do at face value and jump without looking. Do your homework, make a decision, learn from the mistakes, but as is said consistently on the forum....Hang/hike your own hang/hike.

[MDSH]

I read this whole thread and found it very interesting.

FWIW, in my 32' hang in the park with a SLS in 7/32" Amsteel I was nervous because I could hear the tension in the line and feel the strain of loaded deflection.

When I switched to 1/8" material it was solid -- I could feel the residual strength left unused.

Numbers don't lie but who wants to worry about things that don't feel right? Build confidence into your system, I say, so that you can enjoy life.

.

[nothermark]

I think you will find the basic testing setup anchors the line under test by wrapping it multiple times around a smooth cylinder that is large compared to the rope diameter. At least that is what I saw done. That way the strain transfers well so the maximum strain is between the two anchors.

One of the failure issues is tight bends. That is one reason why knots fail. Wrapping a rope over itself is a tight bend by definition.

[MDSH]

It's one thing to know intuitively, "You're gonna die." Many never achieve that level of awareness; so, it is commendable to say it out loud. It does save lives.

It's another thing to heed the inner voice. Superlative wisdom lies therein.

Heed the voice.

Live long and prosper! LOL

.

[oldgringo]

Voice. Not voices. Important distinction.

[MDSH]

Voice. Not voices. Important distinction.

Absolutely! LOL

.

[gmcttr]

Voice. Not voices. Important distinction.

Well then....which one do I choose to listen too?

[jadekayak]

Now keep in mind this is based off of a limited test based on simple number crunching, I have no real world experience with dynaglide(or whoopies slings for that matter, although I will eventually). This is also basing a weight rating from the understanding that splicing degrades the rope by no more than 10%. If there is new information out there debunking that, please feel free to let me know. Alright, enough disclaimer and "I didn't tell you to use dynaglide" Mumbo jumbo and onto the numbers.

I did some playing around with the ultimate hang calculator app on my phone just to get some hard numbers regarding hang angles, weight forces, and what not. I changed the hammock length, ridgeline, and tree spacing around at a given weight and angle and none of the forces changed so I didn't bother with doing that for the actual number testing.

What I came up with was this:

At a 20 degree angle with 600 lbs there is 877.1 lbs of force coming through the suspension

At a 5 degree angle with 200 lbs there is 1147 lbs of force coming through the suspension

At a 10 degree angle with 200 lbs there is 575.9 lbs of force coming through the suspension

At a 10 degree angle with 300 lbs there is 863.8 lbs of force coming through the suspension

Now assuming the whole 10% degradation principle for splicing that brings dynaglide down to a 900 lb breaking strength. Well, utilizing the numbers I provided even a 600 pound person could hang at a 20 degree angle(not bad, but still less than the ideal 30 degrees) and not break dynaglide. It would take a 200-300 pound person hanging at either 5 or 10 degrees respectively to come close or surpass the 900 pounds in the case of a 5 degree angle. I don't know about you but that a very minimal angle! You would have to hang your hammock guitar string tight to even achieve that angle when the hammock is loaded.

I realize this is speculation based on numbers but the numbers are pretty definitive. I also realize that these are based off of static and not dynamic forces but in all honesty, unless you'e Shug practicing your next act of acrobatics, the dynamic forces from getting in and out of a hammock should not even come close to bring these numbers to a failure point. Now I am certainly not trying to force the idea of using dynaglide on anybody, if you don't feel safe using it then definitely don't use it. I was just putting this out there for the folks that were maybe undecided about it and could use some more info in order to make an informed decision. As always, HYOH and Happy Hangin folks!

If you are that concerned about the stresses on the line change up the diameter.
3mm dyneema sk75 has a breaking strain of 1000kgs so I can't complain about strain on the line at my 130kg weight.

Knots decrease line strength,so don't use knots-use BENDS.bends maintain more of the line strength.

BTW 4mm dyneema sk75 has a breaking strain of 1600kgs

Another important factor is safe working load.
This is usually around 20% of rated breaking strain so my 130kg weight at 30° hang angle on 3mm dyneema list well within breaking strain and just over 65% of SWL.