Support Pole/Angle of the Dangle

[Sailor]

Question for the brains greater than mine:
There's been some discussion in the past about the weakness of hiking poles if used to support a hammock, as in they snap. I'm not the sharpest knife on the belt (ask my wife, she'll confirm this), but I'm assuming that trekking poles are plenty strong when the load applied is straight down the pole, and not very strong at all when applied at an angle. So, here's the question for the brains in the outfit.

Assuming the hammock support line extends from the top of the hiking pole, what is the angle, or geometric formula, considering weight in the hammock, length of line, low point, angle of the hiking pole relative the horizon, angle of the support guy lines opposite side of the hammock line, such that the force applied in sum of all the above, pulls straight down the longitudinal axis of the pole?

I'm guessing, absent an advanced degree in a brainiac discipline, that one should be able to angle the pole in the ground relative upright, angle the guy lines, and the hammock line, and get a force on the hiking pole right down the length of the pole, which pole should then easily be able to support the owner's weight.

Help here requested of university, college, and technical school profs, lecturers and hangers on, and other assorted mathematical wise guys.

[pedro]

Okay, I can answer this one, even though I don't have any letters after my name. I do howeer have a lot of experience with this particular problem. The problem with using collapsable trekking poles to support a hammock is that each joint is much weaker than the column on either side of the joint. When you apply load in column to the pole,(like if you were to try to support all your weight on your palms while resting them on top of the poles) the pole will try to flex. If you have a pole with no joints in it, the flexure will be applied, more or less, equally over the entire length of the pole. If, however, there is a weak spot like a joint, that is where it will break. This is even true if you are applying the force in a perfectly straight line along the axis of the pole. Collapsable trekking poles WILL NOT support your weight no matter what you do. Ski poles, on the other hand, are not collapsable, have no joints, are a similar weight to trekking poles, and I can testify that I have hung several nights from them. I'm 160 lbs., and one pole on either end works OK, a bipod on one end works much better. Check my gallery.

[Knotty]

What pedro said.

But if you insist. The center line of the pole should bisect the angle created by the line going from hammock to pole and from pole to ground (when under load).

[Doctari]

I would under (almost) no circumstances use a trekking pole, at least the ones I have seen, to hang from. And as stated above, ones with a joint even less. I use ski poles as my trekking poles, but they have a joint (are adjustable) so I don't think I would trust one to support me, maybe both Secured together (Duct tape?) & as straight as I could get them, maybe with the handles at opposite ends. I would easily trust them to hold up my tarp if I ever had to go to ground tho.

I have 2 different trekking poles, one rather sturdy one, & a wally world "El cheepo" Both bend much more than my ski poles & under less pressure. All are adjustable, but the Wally World one has 3 sections & only takes about 30 - 35 pounds to deform to the point in must be bent back to straight. It has been retired to "Loaner status", after only one 3 day trip.

[bear bag hanger]

Okay, I can answer this one, even though I don't have any letters after my name. I do howeer have a lot of experience with this particular problem. The problem with using collapsable trekking poles to support a hammock is that each joint is much weaker than the column on either side of the joint. When you apply load in column to the pole,(like if you were to try to support all your weight on your palms while resting them on top of the poles) the pole will try to flex. If you have a pole with no joints in it, the flexure will be applied, more or less, equally over the entire length of the pole. If, however, there is a weak spot like a joint, that is where it will break. This is even true if you are applying the force in a perfectly straight line along the axis of the pole. Collapsable trekking poles WILL NOT support your weight no matter what you do. Ski poles, on the other hand, are not collapsable, have no joints, are a similar weight to trekking poles, and I can testify that I have hung several nights from them. I'm 160 lbs., and one pole on either end works OK, a bipod on one end works much better. Check my gallery.

How do you attach the hammock and lines to the pole? I couldn't tell from your pictures. Maybe some close ups of the attachment points to the poles?

[Sailor]

thanks, Pedro & Knotty. I'm not so interested in ski or trek pole, as the the theory for a starting point. Got it that pressure on one side must equal the other side (bisect), but I'm wondering about the pole being in the ground at other than a 90 d angle, top end away from hammock, so that a greater percentage of the pulling force is along the lengthline of the pole. Now, the opposite side stay (really a forestay) applies both an opposite force and a force 90 d to the pole. That's a weakness...So, there must be some optimum angles. They are what I'm wondering...

[Ramblinrev]

I'm no engineer so the numbers of this problem are well beyond me. But one question I would raise has to do with the flexible nature of the setup. It's one thing to angle the support in a static set up where the angles and forces are going to remain constant. But with a dynamic situation like a hammock hang I am not sure I can understand how you would overcome the inherent problems of the joints in the pole. As you load the hammock the weight and angle are going to change as the hammock takes more load and the suspeneiion straps/ropes drop. With a solid pole you can rely on the pole to take those changes all other things being equal. But with a sectioned pole those joints are going to have to be sepcially strengthened to withstand the forces. I wouldn't trust a jointed pole no matter what the angle relative to the ground is. I just don';t see the practicality of it.

[GrizzlyAdams]

thanks, Pedro & Knotty. I'm not so interested in ski or trek pole, as the the theory for a starting point. Got it that pressure on one side must equal the other side (bisect), but I'm wondering about the pole being in the ground at other than a 90 d angle, top end away from hammock, so that a greater percentage of the pulling force is along the lengthline of the pole. Now, the opposite side stay (really a forestay) applies both an opposite force and a force 90 d to the pole. That's a weakness...So, there must be some optimum angles. They are what I'm wondering...

The bisection of which they speak is of the angle between the line from the hammock to the pole, and the line to the ground. To get this bisection you have to angle the pole with the top being farther from the hammock than the bottom. Bisection directs the force down the center of the pole. Anything off center and there is a component of the force NOT down the center that has to be resisted (in physics terms, provide its own countering force) from the pole through an angle not down the center. Depending on the pole material, it may not be strong enough and will buckle.

The larger the angle to be bisected, the less force on the pole. The optimal angle then is 90 degrees, which you quickly see is unrealizable. The longer you can make the tie out from pole to ground, the flatter the angle to be bisected is, and the less force you have on the pole.

Grizz

[Sailor]

To get this bisection you have to angle the pole with the top being farther from the hammock than the bottom. Grizz

Does that angle change or is it the same, and what is it?

[WV]

How do you attach the hammock and lines to the pole? I couldn't tell from your pictures. Maybe some close ups of the attachment points to the poles?

Pedro, let me add my voice to this question about the attachment to your ski poles. My dog's hammock hangs under mine, but there isn't room for it (vertically) unless I hang my hammock impossibly high. If I put a post (ski pole) in one end rope of his hammock, I could move it closer to one tree so it would hang under the head end of my hammock where there's more room. (See photo "Dog Hammock" in Gallery/Homemade Gear - this is without a ski pole support.) I am starting to use a pair of ski poles to spread my own hammock now, instead of using tie-outs on each side. The point of a ski pole is planted under the midline of the hammock, and it slants up (about 45 degrees) to attach to the hammock's tie-out point. I've attached the pole to the tie-out by putting the handle strap through a small loop of 3/16" bungee at the tie-out and bringing the strap loop back over the pole handle. It makes for a loose connection, which is good because the pole pivots some at the ground connection when the hammock moves. I'm wondering if I can also use a pole to partially support one end of the dog hammock, but I'd like to find a simpler way to secure the pole to both the hammock tie-out and the dog hammock support rope that enables separately attaching or detaching either - maybe using toggles or carabiners. Any thoughts? Thanks.
David