Why not use this for a Suspension

[GaHammockGuy]

At Backwoods Daydreamer site, he has this item for sale:





The rating is for "Tech Line is rated to 480 lbs. "

Now if my math is correct, I will (using whoopie slings) tw strands on each side.
Even if I only had one strand, the weight would be distributed across two strands (one strand on each side.

I weigh 200lb. Each strand would be holding 100lb.

Now with the whoopie sling (two strands on each side) each strand would be supporting 50lb.

So why would I not want to use this for my suspension?

Am I missing something, and if so... what am I missing?

I mean, it looks like the rating will be strong enough to keep me off the floor.

Any thoughts?

[taylo]

Nope nope, don't do it. Suspension lines should be rated at least 1400 lb or more - like a amsteel whoopie sling. This would be great for a ridgeline but absolutley not for suspension. Your math might seem logical, but its not. Load calculations are much more complex and vary with angles, weight, and lengths.
However, like I said, it would be an excellent purchase for ridgelines - tarp or hammock.

[fred1diver]

your basic math is correct except that since the weight is not being distributed at a parallel angle to the suspension ( ie the line is not straight) the weight is multiplied I forgot the extra weight added, but it's the same as building anchors for climbing the narrower the v the weight is nearly halved on each line, but the wider the v (just like a hammock suspension) the weight supported by both strands is impressively multiplied, it might work but if you try it make sure you have something soft under the hammock!!!
I'm sure the hammock engineers will chime in soon with the weight each strand will be supporting, you will be surprised by the amout


good luck

[Cranky Bear]

This excerpt was taken from JustJeff's site:

# ...Safely... Hammocks can put hundreds of pounds of force on each support. It isn't simply your weight divided by two...it's a trigonometry function where the cord or webbing is the hypoteneus of a triangle. Using the angle of the support to true horizontal, the force on the support is: h = (.5 x user weight) / sin(support angle). This also brings a few requirements:

* The suspension must be strong enough. Be very careful using cord or webbing that doesn't list a working load or breaking strength. The lowest acceptable range is generally 700 lbs, and some people will not use less than 1000lbs breaking strength. Do not use 550 cord (parachute cord). I've broken 550 cord twice using it on a hammock, and I cut it directly off a parachute so I know it's the real thing.
* The correct knots/lashings must be used. Knots can significantly reduce the strength of cord and webbing. Some knots reduce the strength more than others, and certain knots are designed specifically for webbing. Additionally, some knots will bind when they're weighted and you'll have to cut the support to get the hammock down. So pick non-binding knots or lashings when you choose your system.


For the full reading it can be found here: http://www.tothewoods.net/HammockCampingSuspension.html

[millarky]

something like 720# on each side at 30% for the average male i thought i read once...

[Jsaults]

I am not an engineer, but I seem to remember that a safety factor of four is common in designs (buildings, bridges, etc).

If you are a small person, and can gracefully enter & exit your hammock, and can guarantee that there will be no shock loading you might get away with 480 lbs tensile strength. Remember that with suspension lines at a 30 deg angle to the ground you are basically putting 1x body weight on each suspension piece. So, 150# body weight with a 4x safety factor is at least 600# tensile.

If you do experiment with light suspension line, please make sure that you will have a soft landing. And please video your experiments!

Jim

[Kasuko]

Am I missing something, and if so... what am I missing?

You are missing trigonometry! Yay high school math, see they told you it's be useful but no one ever listens!

You would be correct if the lines were laying perpendicular to the hammock (imagine hanging straight down from a ceiling)

How ever they do not, they are hanging at an angle from the tree. You can think of this hanging as a right angle triangle (The ground, the tree and the suspension line) and we all know our trig for right angle triangles right?
Soh Cah Toa!

Now I could lecture on about the maths but a picture is worth 1000 words so just visit http://whiteblaze.net/forum/vbg/show...792&original=1 and everything will make sense.

Too lazy? Well at 200lbs and 30* hang you have 200lbs PER SIDE! So ya, you could hang using that, but you are pushing the limits. If you move at all then you are not only bound by the static laws of physics but also dynamic laws and I am not explaining impulse on a hammock forum!


EDIT: And no, the whoopie sling doesn't split it in half again. A chain is only as strong as it's weakest link. Same goes for cordage!

[Bubba]

Safe working load is the key I think. Even if the cord has a breaking strength of 480 lbs, a safe working load is probably a third to a quarter of that. That would leave you with 120 to 160 lbs to play with. At 30 degrees the force on each end is equal to your body weight but if you happen to set it up less than 30 degrees, then the force goes up almost exponentially. As has already been stated its probably not a good idea to use it.

[pgibson]

At the weight you listed for your self and if you are looking for a small diameter light weight cord to make whoopies from Dynaglide would be a suitable option. 1.8mm so about the same but rated to 1000 pounds. I make dozens of whoopies from it every month and hang on it myself most of the time.

[gmcttr]

I think it would make the perfect suspension for you and the video you will shoot for our amusement.