"Handy Hammock" - Hammock, no trees
- Thread starter mountainm
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Hey Guest, Early bird pricing on the Summer Moot (29th July - 10th August) available until April 6th, we'd love you to come. PLEASE CLICK HERE to early bird price and get more information.
MagiKelly
Making memories since '67
I'll be interested to hear how you get on. I was sent a review one of these a few years ago but it broke when I got in the hammock. I have to say I found it a bit of a faff to set up and was not convinced that the bracing of the poles added any benefit. I think just plain bars a bit stronger would be fine.
I do keep meaning to try this with my canoe poling poles but have never got round to it.
I made my own freestanding hammock poles. Uses those screw ground anchors as the anchor points. Works really well and stays up all summer in the garden. Bit heavy for carrying around with you though.....
Not sure if there's another thread? Search only found this one.
Just seen that the maker has put alot of info and even given group buy discount to the folks over on HF.
Anyone interested in one of our own?
Sent from my HTC One X using Tapatalk 4 Beta
Just seen that the maker has put alot of info and even given group buy discount to the folks over on HF.
Anyone interested in one of our own?
Sent from my HTC One X using Tapatalk 4 Beta
The group buy seems to be at the old original rrp from when I originally posted this thread. Also seems like the original guy who was peddling these (dizzy) has moved on.
Matt at ukhammocks is selling them too. I'd be interested in one, just at a loss less than the price they're going for.
Cheers
Mike
To minimise weight the design uses a very slender pole. So slender that it becomes too thin to resist bending without help from the cord bracing. The struts sticking out mid height, plus the very high tension that the top-to-bottom cord must be under, prevent the pole from bending in the middle. These cords convert bending force in the pole to tension in the cords by stopping the pole from bowing.
Bending force is created in the pole by the compression it is put under. This reaches maximum at the mid length of the pole. There is zero bending at the ends because there are no solid joints to restrain the pole - it's kept in place at the top by the guys and hammock and at the bottom by just resting on the ground. Each end is free to pivot to a small degree in any direction.
The cords that go from the pole top to the ground pegs carry the tension force imposed by the weight in the hammock (and the very high tension it is put under - which increases dramatically the flatter the lay gets, btw). These do the same job regardless of thickness of the pole.
The same job can be done with a thicker or stiffer pole made of a stronger material. You can then do away with the props's mid-height bracing (whose sole job is to keep the tension cords away from the pole, to make them effective) and the cord up and down the poles. However, unless you get into exotic materials then you lose the weight advantage and compactness.
When a column is very tall and slender, like these support poles, they are believe it or not termed tall slender columns by structural engineers. This is because their ratio of length to thickness exceeds that needed to resist the internal bending force. Columns below this ratio are termed short fat columns - plain English in a complex world, for a change!
You could use a solid ridge bar. That would reduce the number of guys needed as it would reduce the tension they must take by it being in compression. However, the ridge pole would not reduce the compressive force in the pole supports so would not do away with the need for the cord bracing up and down the support poles. However, fixing the top f the support pole stiffly to a ridge pole would induce bending at that joint - but probably not more than at the middle of the supporting pole and so should be able to be ignored as the pole should be thick enough to constrain/resist it. But the ridge pole joint introduces a stiff joint with the pole that, because the pole can no longer pivot freely, also induces shear force - so either pole could shear in two at that joint, where the shear force is biggest.
So yes, the designer had a good idea. And yes, the same can be achieved with 2x2 timbers (as in the earlier photo - you could easily use just one timber pole but use extra guys to stake it out to get the stability), bamboo or carbon tubing of the right size. Titanium would probably do but it would be cheaper to buy a caravan!
Hmm. That's the first time in a decade my engineering degree has come in handy!
You can do the (fairly simple) maths to work out the forces involved and calculate the cross sectional areas and section shapes (tube, I beam etc) and material (section size will differ per material) for the pole to give you a pole that won't need the compressive bracing but unless I'm going into business to sell them then I can't be bothered, sorry! But you get the idea.
A bit of a long answer to a short question - hope it makes sense without diagrams.
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