Physics Question

[Eric Nelson]

So I’m planning on building a 3 hammock suspension system that hangs between three trees, a diy version of the Tree-o, for anyone that remembers that. I’ll be using Dutch’s 1” spider daisy chain webbing for the main body (3x 12’ sections) and my plan was to connect them to each tree using tree straps and a lightweight beaner. My question is how would weight distribution work on that? I’m wanting to use some 1” ratchet straps from HD as to be budget friendly, but having a 500 lbs working load, I’m not sure if each individual strap would experience almost all of the weight, or if it would be evenly dispersed between all 3 straps. Here’s a poorly drawn picture if it helps at all



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[Smckinney0031]

It seems to me like 1 inch straps would not be sufficient to protect trees from damage. That is putting a different type of force on the trees than a regular hammock

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[Cabmanhang]

This is a cool idea. Dynamic forces is the key term. How could you get a proper hang angle to minimize the force applied with that system?

Also, three hammocks bouncing around could provide some really tremendous forces and load to those straps and that would scare me on a one inch strap. I would feel sorry for the trees that you connect to..

[Phantom Grappler]

Tentsile Hammock Tent is an item you can see online. By looking at its specs, you can see what works for them
They set up with a more or less horizontal hang
Straps are parallel with ground, or a flat hang
This kind of setup has lots of stress on straps and tent floor, probably more stress than you’d get on hammocks with a 30* angle of hang
If your rig is setup with a flat hang, spang tight, besides the extra stress due to flat hang, there could be additional stress if occupants discovered any trampoline effects Who doesn’t like having fun?

Probably the weight would be shared somewhat by all straps
I was looking at diagram of hammock with 30* angle of hang The hammock camper weighed 200 pounds and there was 200 pounds force on each end As the hang angle was changed to a flatter angle of hang, the weight on each end increased It did not increase incrementally by addition, it increased geometrically, as hang got flatter, on up to theoretical infinity

I have no background in physics, and used nontechnical words to describe what I’d seen
I got to get up on a Tentsile Hammock Tent, it felt a bit like a trampoline

There are some here on Hammock Forums who have studied physics and higher mathematics

And you can always try it, and experiment a bit

[cmc4free]

Is there a specific set of 3 trees you're planning this for?

If you had the theoretically perfect 3 trees, forming an equilateral triangle, and you used up the entire 12' lengths of daisy chain to meet in the middle at 120° angles, the center points of the trees would be just under 21' apart. In other words, instead of setting up this unusual suspension, you and your 2 friends could just hang normally with each of you using a typical suspension that spans between 2 of the trees. Unless they're really large diameter trees, the 12' straps plus the length of the hammock should be sufficient to span the 21' (at most) provided you can get the suspension high enough on the trees to keep the hammocks off the ground with that long of a span. If you would need less than the 12' of daisy chain to meet in the middle as you proposed, that would mean the trees would be even closer than 21' apart and you wouldn't have to hang a traditional suspension as high.

If you're planning this to be used on "random" groupings of 3 trees, then they'll almost definitely be asymmetrical, meaning each strap will have a different length and they won't meet in the center at 120° angles. Therefore, the forces and sag will be different on each one. And speaking of sag, if your tension adjustment on each leg is limited by the increments of the daisy chain, it may be difficult to get a reasonable amount of tension in the three "spokes" to keep the weight of three hangers off the ground. Plus with 3 hangers sharing the same suspension system there could be a lot of bouncing and jiggling as others have mentioned.

There's no harm (hopefully) in trying out new and creative ideas. But if you try and it doesn't work as you intended, you can always consider the more traditional approach with each of you hanging between 2 trees. You'd need 6 daisy chain straps (or any type of straps) and 6 carabiners, as opposed to 3 tree huggers, 3 daisy chains, and 9 carabiners (by my count... you didn't explicitly state how you intend to attach the hammocks to your web).

[Eric Nelson]

Is there a specific set of 3 trees you're planning this for?

If you had the theoretically perfect 3 trees, forming an equilateral triangle, and you used up the entire 12' lengths of daisy chain to meet in the middle at 120° angles, the center points of the trees would be just under 21' apart. In other words, instead of setting up this unusual suspension, you and your 2 friends could just hang normally with each of you using a typical suspension that spans between 2 of the trees. Unless they're really large diameter trees, the 12' straps plus the length of the hammock should be sufficient to span the 21' (at most) provided you can get the suspension high enough on the trees to keep the hammocks off the ground with that long of a span. If you would need less than the 12' of daisy chain to meet in the middle as you proposed, that would mean the trees would be even closer than 21' apart and you wouldn't have to hang a traditional suspension as high.

If you're planning this to be used on "random" groupings of 3 trees, then they'll almost definitely be asymmetrical, meaning each strap will have a different length and they won't meet in the center at 120° angles. Therefore, the forces and sag will be different on each one. And speaking of sag, if your tension adjustment on each leg is limited by the increments of the daisy chain, it may be difficult to get a reasonable amount of tension in the three "spokes" to keep the weight of three hangers off the ground. Plus with 3 hangers sharing the same suspension system there could be a lot of bouncing and jiggling as others have mentioned.

There's no harm (hopefully) in trying out new and creative ideas. But if you try and it doesn't work as you intended, you can always consider the more traditional approach with each of you hanging between 2 trees. You'd need 6 daisy chain straps (or any type of straps) and 6 carabiners, as opposed to 3 tree huggers, 3 daisy chains, and 9 carabiners (by my count... you didn't explicitly state how you intend to attach the hammocks to your web).

Thanks for the insight. And yes the plan is to hang 3 hammocks between the 3 daisy chains with beaners, so on each strap there would be 2 hammocks clipped on. I don’t have any perfect trees, the idea is to be able to take it anywhere I can find appropriate trees. Being college age it makes it easier and more fun for friends of mine that aren’t exactly hammockers. I’ve actually done a similar set up with a homemade contraption but with not so good results. I larks-headed 3 amazon daisy chain straps onto a 3” steel ring and attached it to trees using 2” ratchet straps. The setup took forever to hang and probably weighed 20 lbs. The only thing I’m worried about now is how much weight will be put onto each tree strap. Having 500lbs working load I’m not sure if say, I had 600 pounds in the suspension system, if each tree strap would have only 200 or so pounds of force, or if each one would be supporting closer to 600 pounds


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[cmc4free]

Thanks for the insight. And yes the plan is to hang 3 hammocks between the 3 daisy chains with beaners, so on each strap there would be 2 hammocks clipped on. I don’t have any perfect trees, the idea is to be able to take it anywhere I can find appropriate trees. Being college age it makes it easier and more fun for friends of mine that aren’t exactly hammockers. I’ve actually done a similar set up with a homemade contraption but with not so good results. I larks-headed 3 amazon daisy chain straps onto a 3” steel ring and attached it to trees using 2” ratchet straps. The setup took forever to hang and probably weighed 20 lbs. The only thing I’m worried about now is how much weight will be put onto each tree strap. Having 500lbs working load I’m not sure if say, I had 600 pounds in the suspension system, if each tree strap would have only 200 or so pounds of force, or if each one would be supporting closer to 600 pounds


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Kind of hard to say, and it's going to vary from situation to situation. Each tree (and therefore each strap) is going to be under a different load depending on the respective length of each leg and the weight of the person hanging from it. I don't believe the forces will equalize just because the center point where the straps come together is not fixed. Then again, I could be wrong. I am an engineer, but more of a practical or intuitive one than one who's great at drawing free body diagrams and doing calculations. Perhaps that means I'm "not a very good engineer." Shrugs.. I have strengths in other areas.

As others have said and as the Hammock Hang calculator will show you, with a traditional setup the lateral forces increase rapidly as the suspension angle becomes flatter. But with the setup you describe, by the time all the slack is taken up, each strap coming off a tree might be closer to the ideal 30° than one might think. I doubt you'd get to 30°, but it could very well be 15-20°. As far as breaking straps or being kind to the trees, you're probably better off allowing for some sag/angle in the 3 daisy chain straps than trying to get each one ratchet strap tight.

[jeff-oh]

This is a fairly simple loading problem. The set-up that produces the lowest load at the trees is under the following conditions:
1) 3 equal distant trees,
2) Equal length straps
3) Equal weight people and hammocks.

Under these conditions the load (weight of people) will react at the center of mass... i.e. the 3 point intersection in the middle. Further this load will be equally distributed to the three trees. Thus the load at each tree is 2 times higher than a normal hang. To understand this. Normal: 1 person two hang points each hang point = 1/weight of person. Proposal 3 people 3 hang point. Each hang point take full weight of person.

Now add in the hang angle. If you want to hang at a 30 degree angle then the above is true... but this puts your head or feet 1/2 the length of your hammock lower in the middle. To avoid this, the tension in the straps must increase to bring the middle up. To have an angle such that the feet are 10" higher than the head would mean that you have to have a hang angle of 4.25 degrees.

At 4 1/2 degrees the tensile load in the strap would be ~ 13.5 times your body weight. Thus for three 200 lbs hangers the load in the straps would be 2700lbs. This is the minimum load. Once the angles go off ideal and the people shift then the load in the straps go up even more and possibly by multiples. Put a minimal safety factor on that and your looking at a strap that needs to be rated at 15,000 lbs and more.

Phamtom is right, your set-up is not that different than tensile tent. This makes since when you think about it. Tensile tent does not put those massive straps on their system to hold the tent... the straps are there to hold the people. Your proposed system, structurally, is no different. Sorry, but I'd predict, even the spider straps would break. Or most likely the center would droop down so low you would not like the angle of the hammock.

[jeff-oh]

Up date, I assumed you were hanging, in-line with the straps. Hanging around the perimeter, would negate the need to stress the straps up to get a level hang. Though the min load would still be body weight+. Another item to deal with is the hammock will shift positions as a person gets up and the new center of mass is found. This could be interesting when someone get up in the middle of the night to pee and the other two suddenly drop several inches. Also, each of you will feel every little twitch and movement of the others.

This is doable, but as you go to a shallower hang angle the loads multiply very quickly. Perhaps use the HD ratchet but replace the strap with Kevlar or UHMWPE strap or high loading Poly-etheline.

[Eric Nelson]

Up date, I assumed you were hanging, in-line with the straps. Hanging around the perimeter, would negate the need to stress the straps up to get a level hang. Though the min load would still be body weight+. Another item to deal with is the hammock will shift positions as a person gets up and the new center of mass is found. This could be interesting when someone get up in the middle of the night to pee and the other two suddenly drop several inches. Also, each of you will feel every little twitch and movement of the others.

This is doable, but as you go to a shallower hang angle the loads multiply very quickly. Perhaps use the HD ratchet but replace the strap with Kevlar or UHMWPE strap or high loading Poly-etheline.

Here’s a picture of the long out-of-business Tree-o. This is what I have already duplicated with nylon webbing and 2” ratchet straps in the past. Of course I’m trying to remake it with the lightweight spider webbing and tree strap instead. The bouncing isn’t so much of a problem as I doubt it will be slept in, just more of a day thing to hang with friends. I was hoping having the weight dispersed would mean I could use ratchet straps and cut the hooks off of them and attach an aluminum beaner, but after all the insight it seems I should just wait until I can purchase Dutch’s 3000lbs 8’ tree straps



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