The truth about dynaglide and safety...

[mudsocks]

No one has stated it and maybe it's because it seems obvious but wouldn't the most likely point of failure be the hammock itself?

[TheIrishmanHangeth]

No one has stated it and maybe it's because it seems obvious but wouldn't the most likely point of failure be the hammock itself?

Yep, which is part of why I introduced the EXTREMELY unlikely scenario of a 600 lb hanger to the equation. I don't know of anybody that weighs that much that would be physically capable of hanging in a hammock, nor is there even a hammock fabric(that I know of anyway) that is capable of holding that much weight, other than maybe a double layer of canvas lol. So, in theory of course since I haven't done any real world testing, anyone who is likely to actually go set up a hammock and lay in it should be safe to use something like spliced dynaglide as a means of suspension.

[nothermark]

Heavier pack cloth or Cordura would make a hammock for 600 lbs. I could see a double rated at that. ;-)

[Rain Man]

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).

I realize this is speculation ...

Apologies in advance, but to me, you hit the nail on the head. Twice.

Don't kid yourself that just cause math says it's OK that it actually is OK.

Not just math, but "simple number crunching." Scary.

Failure is caused by tight radius turns over things like another rope or small hardware. Given those derating factors and a preferred safety factor of at least 5:1 and better yet 10:1 I would hang close to the ground with very light tackle like you are talking about as sooner or later you will be on it.

Agreed. Definitely hang over ground so soft you might as well tent.

I'm an ex-caver and did some "vertical caving" in my younger years. I know of cavers who died, were injured, or had very scary experiences doing analyses like this one.

And in this case, for what? To save a few grams?

Rain Man

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[warbonnetguy]

I have pulled structural ridgelines as tight as I could get them (spanning about 20', as I recall), and when I attached my hammock, my weight pulled the ridgeline angle down to about 15°, so I figure whatever line I use needs to hold about twice my weight. That lets me use dynaglide with at least a 3:1 safety factor.

In my experience, i've not been able to get the angle (when weighted) to get below 20 deg no matter how tight i've pulled the suspension, i roughly measured this with a protractor. (didn't try it with whoopies though). Also, i've found that usually adding more weight will cause the angle to decrease farther in many cases.

[warbonnetguy]

In the testing i've done, amsteel tied in a fig 8 reduces break strength by about half, I've read that other places too, but i have personal test results of a single strand of amsteel 1/8" tied in a fig 8 loop breaking at around 1200 lbs while the tensile strength is listed around 2100 lbs or slightly above, same aprox results with 7/64 tied as a fig 8 (failure at around 750 lbs but rated at 1600 or so). when spliced instead of tied i'm getting breaking strengths right at or sometimes even slightly above the listed tensile strength (for instance spliced 7/64 dogbone broke at 1700 while the listed tensile strength is 1600....the type of rope being used has alot to do with it, a knot in 10mm nylon climbing rope would have different strength reduction numbers than the same knot tied in much smaller diameter dyneema

That's a bit of an exaggeration. There are a lot of variables (i.e., type of rope; knot you've tied). But when it comes to any knot used for climbing, the only knot that gets that low is a bowline. Many climbing knots are going to reduce the strength no more than 30%.

http://www.paci.com.au/downloads_pub...tute_Tests.pdf

I tie a Double Figure 8 on my adventure challenge course, and testing shows the knot only reduces a ropes strength by 18%.

[warbonnetguy]

As well a suspension that is pulled very tight and then sags to 30 degrees when loaded is not the same as a suspension that is hung with a 30 degree sag. It will be under extreme loads with the tension that will be put on the system. The math used in the calculator at The Ultimate Hang is functioning on the premiss that your measuring the angle of an unloaded/unweighted hammocks suspension.

Paul, who told you that? Maybe we need grizz in here to clear this up I was under the impression that the angle "when weighted" is what the load calcs are based on. A hammock suspension pulled horizontal (zero deg) and then weighted with a 200 lb person would have a weighted suspension angle of around 20-25 deg, but if you used zero for the angle calc instead of 25 because it was zero when empty, the numbers wouldn't add up. (according to the calc, 200 lbs of weight and zero deg angle would give you an actual weight tens of thousands of lbs meaning you'd then expect that if you pull your suspension to a zero deg angle and get in that it would snap instantly). I think it has to be based solely on the suspension angle when weighted for things to make sense.

[WV]

In the testing i've done, amsteel tied in a fig 8 reduces break strength by about half, I've read that other places too, but i have personal test results of a single strand of amsteel 1/8" tied in a fig 8 loop breaking at around 1200 lbs while the tensile strength is listed around 2100 lbs or slightly above, same aprox results with 7/64 tied as a fig 8 (failure at around 750 lbs but rated at 1600 or so). when spliced instead of tied i'm getting breaking strengths right at or sometimes even slightly above the listed tensile strength (for instance spliced 7/64 dogbone broke at 1700 while the listed tensile strength is 1600....the type of rope being used has alot to do with it, a knot in 10mm nylon climbing rope would have different strength reduction numbers than the same knot tied in much smaller diameter dyneema

Paul, who told you that? Maybe we need grizz in here to clear this up I was under the impression that the angle "when weighted" is what the load calcs are based on. A hammock suspension pulled horizontal (zero deg) and then weighted with a 200 lb person would have a weighted suspension angle of around 20-25 deg, but if you used zero for the angle calc instead of 25 because it was zero when empty, the numbers wouldn't add up. (according to the calc, 200 lbs of weight and zero deg angle would give you an actual weight tens of thousands of lbs meaning you'd then expect that if you pull your suspension to a zero deg angle and get in that it would snap instantly). I think it has to be based solely on the suspension angle when weighted for things to make sense.

Wondered about that, myself.

[BillyBob58]

The numbers don't lie..... However, dynaglide, or any other rope, going around something small, creating a very small radius can simulate a lot of what makes a knot degrade the strength of the line. For instance, dynaglide threaded through a Dutch whoopie hook.

So, I guess it's a good thing that there is strength to spare because dynaglide and whoopie hooks is exactly what I've been hanging from for over a year. For reference, I'm a 200 pounder but always maintain a 30 degree angle on my suspension.

There is what you mention, plus: what about the Lark's Head that cinches down on the hammock end knots or cinches down after the rope comes out of an end channel? Is that a knot, does it count as one? Because I think I remember a thread here where some one showed than any kind of knot vastly degraded Amsteel far more than we are used to thinking happens. I think it was some huge % decrease in strength, like 60-80%. ( but I see in this thread that WBG is showing more like 50% with a fig 8 knot, a more reasonable %)

[warbonnetguy]

Good point BB, i think the larks head that attaches a whoopie to the hammock would decrease strength some as there's a somewhat sharp bend in the rope there...no telling how much that degrades the strength of a whoopie, but i'd imagine it does have some effect.