# Thread: Force calculation for a unusual hang

1. Originally Posted by oldgringo
I think if you incline the bipods so that the angle of incidence between the hammock suspension and the bipods is reduced, the bipods will take more of the load, reducing the load on your anchor points. Grizz, what say you?
yeah, Youngblood busted me. Two things happen, you lower the eyebolts so the angle of cord to ground is less, and you increase the angle between hammock and bipods---which is where YB caught me out.

Originally Posted by Youngblood
Grizz, will it not translate into 125 lb vertical force at the eyebolts and we will not know the horizontal force without knowing the angle of the hammock suspension rope/webbing?

Probably the minimum force would be with a hammock suspension rope/webbing at a 30 degree angle, which would make the force on the hammock suspension rope 250 lbs (125 / sin (30)) with a horizontal component of 216.5 lbs (125 / tan (30)). If I'm figuring it right, it would be 216.5 lbs or more if the hammock rope/webbing suspension angle was less, instead of the 125 lbs you used in your example. If they are using a hammock with a structural ridgeline it could get up to 250 lbs pretty easily.
Busted! Comes from trying to dash off trig and a diagram between meetings. Coulda shoulda got the formula from Smee's famous WB diagram giving shear forces.

So, the methodical way is to compute the horizontal shear, divide by the cosine of the angle of the cord, and voila! A whole lot of force on that stake.

Originally Posted by matto
I think that's a good thought. Or why not use tripods for better stabilty?
Tripods with a rigid pole between them, and the hammock hanging from the rigid pole is great. Someone showed that recently in bamboo (I should know who that is but all I can do these days is an occasional power skim of HF). Tripods might help without a rigid pole, but you'd have to have one of the legs in aligned with the cord to ground, facing in towards where the hammock goes, and not be interfering with the hammock. Which means the tripods would have to be pretty far separated to avoid interfering with the hammock. Which means that the tripods would have to be higher to get the hammock off the ground. Which means this is probably a jobs program for sherpas.

Also, for the stakes, making the line longer (i.e. staking down farther away from the hammock) would be an easy way to reduce the amount of "pull out" force. The stake is going to hold better if there's less upwards and more sideways force acting on it.
That's right. Increasing the line reduces theta and increases cos(theta).

One more thing you can do is use multiple lines and stakes to share the load. You want them all pretty close to each other because the wider the angle of the cord from center, the less effective it is at giving opposing force in the direction that needs opposition.

Originally Posted by PuckerFactor
Spanish Windlass is the term, I believe, Grizz.

PF
Thanks! This means I learned something today. Can I go home now?

3. what a great conversation, thanks!!

So it sounds like the bipods only change the direction of the tension forces on the rope (using 7/64 amsteel blue btw).

I guess my searching skills could use a little work. Smee's famous WB diagram is a great resource and would have gotten me a long way for sure. It is very interesting how the tensile forces decrease quickly as the angle changes. This makes me want to heighten the eyebolt to increase the θ angle and thus reduce the tensile forces.

I have some other ideas that I will comment on later. Work calls...

4. Thanks Grizz and Youngblood, now I have a headache. I guess all of that is the mathematical formulas behind "the angle of the dangle" theory...I'm glad somebody can figure all that out. If these didn't cost so much, I'd have a pair for when trees aren't available.

http://treemounthammocks.com/bipod_tree_system.html

5. if anybody is interested, during testing i've done, i've not been able to get any less than a 25deg angle, i think it very unlikely that someone could hang at less than 25 without some kind of special rigging, 3:1 etc.

6. Originally Posted by warbonnetguy
if anybody is interested, during testing i've done, i've not been able to get any less than a 25deg angle, i think it very unlikely that someone could hang at less than 25 without some kind of special rigging, 3:1 etc.
I am curious what your motivation is for the low angle hang...

7. Originally Posted by james90755
I am curious what your motivation is for the low angle hang...
there is none (except for maybe making possible a really long span), but as the angle gets lower/flatter, the forces involved start to become exponential, putting more force on your suspension. at 30 deg, there is about bodyweight on each rope. at 15 deg, the force on each hammock rope is almost 200% of bodyweight.

8. ## This may be of help.

The force diagram was posted here some time ago (thanks to the OP!). If your hammock suspension lines form a 30 deg angle to the ground, you place 1X your weight on each anchor point - in your case, the peak of the bipod. So I am assuming that the anchor line to the ground anchors, if also 30 deg, would have to withstand the same 1X loading.

The second pic is a diagram of an anchor system I have used with success. It is based on a continuous loop of Amsteel, 12-15' total circumference and three long stakes. Arranged in three loops and run through a carabiner it self-adjusts so that the force is distributed equally on each stake.

This is an old trick for ice climbers who may have sketchy anchor placements. I personally am not a fan of the stakes aligned in a row, "pickett" style. I tried it once and woke up with the first and second stakes hanging in the air with my weight anchored by the third.

As for stakes, I have been using the big orange or yellow contractor stakes available at Slowes or Home Despot.

Jim

9. ## Found a pic of my layout

This was from a couple of years ago before I discovered Amsteel on HF, so the continuous loop is actually a NRS canoe tie-down strap.

Jim

10. Originally Posted by GroundHog
If these didn't cost so much, I'd have a pair for when trees aren't available.

http://treemounthammocks.com/bipod_tree_system.html
So I am not the first to think of this option. I would gladly buy vs. make if the price was reasonable. My current design at 50" height is <\$25. I am now thinking about some 3/4" square tube inside the 1" square tube as an extension that should get me up to ~80"... and still less than \$40 for the whole shootin match.