Pole support for hammock on open ground.

King Rat

King Rat

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I am drawing up plans for some nesting poles I can carry on the bike to put a hammock up where there are no trees or suitable supports.
2mm wall aluminium 40mm, 35mm and 30mm I was going to use. Drill say 20mm overlap for securing bolts for each section. That would give 1.74m of height if I went with 600mm lengths.
Alternative 500mm lengths and add an extra length of 25mm.

Anyone done similar and got any feedback on my material choice? I know the system works, loads of American hammock hangers doing it, one I saw with a broom handle each end, but it was very low hanging.

I am sure 2mm wall should be strong enough. Any engineering input as to my choice please?
 
They going to collapse Simon. A pole in the ground, (that you would want to carry on a bike), aint gonna suspend a mans weight.
Unless your going to very expensive materials. Or scaffolding.. Plus . you must factor in the state of the ground they are going into . Post-crete is good but heavy.....JMOOC :unsure:
 
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It'll have to be an A frame, unless you're really good at balancing in your sleep.
 
I’ve got one of these superb hammocks. Personally I think they’re a LOT more comfortable than a traditional one. It can also be “ put up “ on the floor like a tent if there’s no trees with a couple of short poles ( or trekking poles ).
 
MickDB1 said:
They going to collapse Simon. A pole in the ground, (that you would want to carry on a bike), aint gonna suspend a mans weight.
Unless your going to very expensive materials. Or scaffolding.. Plus . you must factor in the state of the ground they are going into . Post-crete is good but heavy.....JMOOC :unsure:
Click to expand...

Spot on.
 
If two crutches will support a well nourished cripple, four crutches, or their equivalent, will support a hammock and its occupant.
It'll need two a frames, in compression, with the guy line over the top, to the ground in tension
 
Thank you for your worries chaps, but there is plenty on the web about Americans, nealt twice my weight, being supported by what they call EMT (aluminium electical trunking.... the secret is the poles HAVE to lean out at the top, so the foot is inboard of the top. Two guys each end support the sideways and compression moments and the ridgeline keeps the pole top in tension towards each other....

Here is one in use - you can use one of these each end, but the Tensa system is about £200 to buy.


This one is using a broom handle for the support.... it is all down to the angles used in the setup so that there is no bending force on the pole, just compression through it's length. Clever.


This is the commercially available version that I have been following the development of over the last decade. It is proven, but very expensive which is why I am looking to build a couple f poles and make my own - I don't know how thick the alloy poles have to be, the EMT this commercial one started out as was 1.25" diameter and 12g aluminium used by electricians in USA and just bought from an electrical wholesaler - used as a single 6ft length each end. Hence my looking for a collapsible option using the 2mm aluminium tube stock, which comes in 5mm increments, meaning there is little gap between each section (1mm total, and only 0.5mm each side). I might have to make some kind of bush to take up the slack that will still slide - epoxy built up and sanded back to fit perhaps?

TENSA have devised it so the poles point INWARDS at the bottom. Something to prevent the poles sinking into the ground under the pressure - a small disc of plywood would be sufficient, or a T piece of aluminium that the pole can fit into, just to spread the load. That could be pegged if you're worried - but the guy who devised the TENSA system just guys the bottom of his poles out to the same stakes that hold the poles up so they can't slide inwards.

 
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SBD said:
en.wikipedia.org

Euler's critical load - Wikipedia

en.wikipedia.org en.wikipedia.org

calcresource.com

Column Buckling

Find column critical buckling load, using the Euler's formula. Theoretical background. Imperfections. Examples.
calcresource.com calcresource.com

Gives a buckling load of 36kN for 40mm square tube.

You’re not that heavy.

You will need good tent pegs and strong guy ropes.
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ROUND tube should be stronger than square tube I would have thought - or will it be much the same?
 
Greg Masters said:
Round is lighter for the same gauge and section
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I wonder how thick walled hospital crutches are - the ones they give you for a broken leg? Telescopic handle to adjust height ones. They support a big, heavy, second row forward swinging his whole weight through between a pair - so similar to lying in the hammock, full weight on the metal pole part of the support.

Is the smaller diameter tube (25mm x2mm wall) going to be stronger than the 40mm x 2mm? Maybe 3x 600mm sections of 25, 30 and 35 would be better than the 40, 35, 30 first suggested?

Once I have made a decision on which sections to get I will do a step-by-step on making the system and put it up for all.
 
Sorry, I just clicked “square” on here.

calcresource.com

List of Moment of Inertia (second moment of area) calculators

Calculate the Moment of Inertia (second moment of area) using the available tools in this page, for many different shapes.
calcresource.com calcresource.com

You can do the sums easily with these websites

You can probably get away with 20mm x 1mm tube, provided you don’t stick it in the ground.
 
SBD said:
Sorry, I just clicked “square” on here.

calcresource.com

List of Moment of Inertia (second moment of area) calculators

Calculate the Moment of Inertia (second moment of area) using the available tools in this page, for many different shapes.
calcresource.com calcresource.com

You can do the sums easily with these websites

You can probably get away with 20mm x 1mm tube, provided you don’t stick it in the ground.
Click to expand...
Brilliant thanks SBD - the 2mm wall will be plenty then.

I shall get cracking on that little project next week. get the tube ordered, or possibly ride down and fetch it. I will buy the Tensa boomstakes because they are steel reinforced at the peg holes - alloy tears otherwise, the chap found out the hard way during his testing and development. Mike, the editor of Cafe Racer will be able to get them for me and he'll post them over. :D
 
( @King Rat )

Simon, I have four of these poles from a German brand Tatonka for setting up my tarp. They come in 5 different lengths from 1.6m - 2.6m.
They are made of 5 aluminium sections, with each section being slightly tapered so that they can be pushed inside each other and capped of at each end, resulting in a single piece tube.

IMG_3720.jpeg

IMG_3722.jpeg

IMG_3729.jpeg

IMG_3964.jpeg

I am however not sure if these would be strong enough to take the weight of a man suspended in a hammock, as tube walls are circa 1mm thick.

But this does give you some food thought and possibly another idea.
 
Assuming I haven’t done anything daft, the sums say 2m long, 2cm dia, 1mm wall, 70GPa ally tube will buckle at ~450kg per pole, which should offer some factor of safety, but lots of things can affect this, including shock loads, the pole being damaged, point loads such as screws, other stress raisers, etc.

Sleeving the poles together will hugely reduce this as the sections will not be perfectly aligned and perfectly straight, and the joints are stress raisers.

At least if it doesn’t work, you’ve not got far to fall.

Do try it at home before relying on it on a hillside somewhere!
 
SBD said:
Assuming I haven’t done anything daft, the sums say 2m long, 2cm dia, 1mm wall, 70GPa ally tube will buckle at ~450kg per pole, which should offer some factor of safety, but lots of things can affect this, including shock loads, the pole being damaged, point loads such as screws, other stress raisers, etc.

Sleeving the poles together will hugely reduce this as the sections will not be perfectly aligned and perfectly straight, and the joints are stress raisers.

At least if it doesn’t work, you’ve not got far to fall.

Do try it at home before relying on it on a hillside somewhere!
Click to expand...
Thanks for doing that - I did try to use the linked calculators you provided but after putting in the length I then fell at the next hurdle. I have no idea what the required figures were!
 
EVskij said:
( @King Rat )

Simon, I have four of these poles from a German brand Tatonka for setting up my tarp. They come in 5 different lengths from 1.6m - 2.6m.
They are made of 5 aluminium sections, with each section being slightly tapered so that they can be pushed inside each other and capped of at each end, resulting in a single piece tube.

View attachment 348042

View attachment 348043

View attachment 348044

View attachment 348045

I am however not sure if these would be strong enough to take the weight of a man suspended in a hammock, as tube walls are circa 1mm thick.

But this does give you some food thought and possibly another idea.
Click to expand...

Thanks - my poles are twice your thickness, or at least the ones I am looking at are. I think I shall give it a go!
 
I was thinking two struts and one tie, not one strut and two ties, lighter and more compact, though I'd be worried about going bump in the night.

Crutch dimensions:- Outer O/D 25.35mm I/D 22.68mm wall thickness @ 1.40mm
Inner O/D 22.25mm I/D 19.62mm wall thickness @ 1.30mm
There's nylon bushes that take up the little slop.
Though there's only two tubes that slide together, you could go- inner/ outer/inner/outer, so less compact (but cheap!)
 
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