The truth about dynaglide and safety...

[TheIrishmanHangeth]

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!

[Trail Runner]

This is also basing a weight rating from the understanding that splicing degrades the rope by no more than 10%.

This is what I was taught in the service & I've read the same in different knot publications. Splicing is definitely the best way to preserve the strength of a line. All knots reduce the strength of a line by at least 40% ex: a square knot reduces the strength by 60%.

Cool post, thanks.

[Goose 1]

All knots reduce the strength of a line by at least 40%.

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]

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%.

[MAD777]

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.

[TheIrishmanHangeth]

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.

And that's kind of my point. Under normal hanging circumstances there should be no reason why even someone who weighs 400-500 pounds( well above the weight of the "average" hanger) can't hang with dynaglide and feel safe and secure doing so.

[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 %)

[TheIrishmanHangeth]

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 %)

If this were the case, then, even 7/64 wouldn't have the "necessary" safety ratios as that simple larkshead would drop it to less than 800 pounds along with the 10% for the splice. It seems very unlikely that a larkshead would decrease the strength by that much.

[WV]

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.

[TheIrishmanHangeth]

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.

You pull the ridgeline or suspension as tight as you can. I ask because you could have a guitar string tight and still have a 30 degree hang angle.