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  1. #11
    Frawg's Avatar
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    Problem is that "guitar string tight" is hard to quantify. I set mine more like a washtub bass.

    Barring stretch, as long as the ridgeline is taut the hammock lay should feel the same regardless of hang angle. Hang angle does affect the tension in both the ridgeline and the lines to the trees, though. We tend to gravitate () to a 30* angle because that sets the tension in the suspension lines at about your body weight. It's the ratio of ridge line length to hammock length that affects the lay more. Somewhere around .85, give or take, seems to be the going number.
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  2. #12
    beep's Avatar
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    Quote Originally Posted by Frawg View Post
    Problem is that "guitar string tight" is hard to quantify. I set mine more like a washtub bass.
    Well said!!
    "The more I carry the happier I am in camp; the less I carry the happier I am getting there" - Sgt. Rock

  3. #13
    Frawg's Avatar
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    BTW, Professor Grizz did the math for us in this old post from 2007.
    - Frawg

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  4. #14
    New Member matto's Avatar
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    Quote Originally Posted by Tjalling Weideman View Post
    I invite you to walk in my shoes f or a while. I' am a Dutch civil engineer and think that my pictures of the equilibrium of forces at the end of the hammock are right.
    This US civil engineer agrees with your diagram!

    Quote Originally Posted by Frawg View Post
    PMFJI... TW, I believe matto was commenting on his own theory, not challenging yours. Seemed to me he was just trying to square his inuition with what you'd posted.
    Exactly right. I haven't really figured out what exactly my theory is yet but I thought I'd share since it's been gnawing at my engineer gene.

    I suspect... and I go here with great trepidation... that the distribution of one's body weight (heavy torso) in the hammock changes the free body diagrams a bit. That is, it's not necessarily 1/2W acting on each tree. Whether this answers my first question, I'm not sure.

    Before you blast me completely, consider this: the tension in the RL changes considerably from when you're sitting in the hammock (with feet off the ground) to lying in it. Why?

    Like I said, I haven't really fleshed this thought out fully yet, so please be kind.

    (I've also considered that because it's an asym hammock there could be a third dimension to consider... but I just can't bring myself to start drawing the FBDs after work hours!)

  5. #15
    Frawg's Avatar
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    Quote Originally Posted by matto View Post
    Exactly right. I haven't really figured out what exactly my theory is yet but I thought I'd share since it's been gnawing at my engineer gene.
    More than a few of us are engineers, physicists, mathematicians, etc.. I'm an EE myself.

    I suspect... and I go here with great trepidation... that the distribution of one's body weight (heavy torso) in the hammock changes the free body diagrams a bit. That is, it's not necessarily 1/2W acting on each tree. Whether this answers my first question, I'm not sure.
    You're right, of course, and are actually starting to look beyond a simple first order analysis, IMO. The usual numbers we bandy about come from a simple analysis, where the hang is symmetrical, the lines and hammock don't stretch and the hammock takes the shape of a simple catenary (hyperbolic cosine form). Given the load margins we want to maintain, the simple analysis comes close enough.

    Before you blast me completely, consider this: the tension in the RL changes considerably from when you're sitting in the hammock (with feet off the ground) to lying in it. Why?
    Heh heh... this forum is a no blasting zone! But to answer your question, perhaps because the lines stretch, and the hang angle changes. Also, if you sit off center, youve now loaded the system asymmetrically. Predicting the final hang parameters of a loaded, stretchy hammock with (less) stretchy lines wouldn't be a trivial exercise, IMHO. At least not for me...

    (I've also considered that because it's an asym hammock there could be a third dimension to consider... but I just can't bring myself to start drawing the FBDs after work hours!)
    Being a CE you might have encountered tensioned fabric structures... brush up on your continuum mechanics and have at it!

    Cheers!

    Edit: Maybe this discussion should move over to the Suspension Forum, since it's gotten more general than the OP posed. Might be best not to dilute the Warbonnetness of this forum.
    Last edited by Frawg; 06-09-2010 at 17:26. Reason: clarification
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  6. #16
    Senior Member mtncmpr's Avatar
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    Quote Originally Posted by matto View Post
    This brings up something that's been on my mind.

    As the force diagram shows, the angle of the suspension only effects the tension in the ridgeline -- not the fabric. So why then does getting the right angle make such a difference to the comfort of the lay?

    In theory, if the WBBB had a slightly shorter RL you hang it "guitar string tight" and get a perfect lay every time.

    (I fully expect that this theory is wrong. I'm hoping someone can explain why. Something to do with being able to shift your body weight when in the hammock maybe?)

    Apologies if I'm treading over old ground here.

    Thanks for asking matto. This has been gnawing at me too. I just couldn't quite figure out the best way to ask.





    Quote Originally Posted by Frawg View Post
    Problem is that "guitar string tight" is hard to quantify. I set mine more like a washtub bass.

    Barring stretch, as long as the ridgeline is taut the hammock lay should feel the same regardless of hang angle. Hang angle does affect the tension in both the ridgeline and the lines to the trees, though. We tend to gravitate () to a 30* angle because that sets the tension in the suspension lines at about your body weight. It's the ratio of ridge line length to hammock length that affects the lay more. Somewhere around .85, give or take, seems to be the going number.

    Thanks for the answer Frawg. I think I understand now.


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  7. #17
    New Member matto's Avatar
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    Quote Originally Posted by Frawg View Post
    The usual numbers we bandy about come from a simple analysis, where the hang is symmetrical, the lines and hammock don't stretch and the hammock takes the shape of a simple catenary (hyperbolic cosine form). .... Predicting the final hang parameters of a loaded, stretchy hammock with (less) stretchy lines wouldn't be a trivial exercise, IMHO. At least not for me...
    For me either, Frawg. Simplifying assumptions are essential to any analysis; the trick is making the right ones. I'm not sure I'm up to the task of tackling all of the questions I've raised at the moment, but I'll continue to ponder them and post any flashes of brilliance.

    Quote Originally Posted by Frawg View Post
    Edit: Maybe this discussion should move over to the Suspension Forum, since it's gotten more general than the OP posed. Might be best not to dilute the Warbonnetness of this forum.
    Yes, I hope the OP got a satisfactory answer. Sorry to nerd-jack the thread!!

  8. #18
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    Quote Originally Posted by matto View Post
    consider this: the tension in the RL changes considerably from when you're sitting in the hammock (with feet off the ground) to lying in it. Why?
    That is because the load of your body weight is spread out over more of the hammock when you are laying versus sitting. That causes the angle(s) of the hammock fabic to change. This is more difficult to visualize when the ridge line is attached directly to the hammock knots as opposed to a ridge line that is attached a few inches above the hammock knots.

    We often state that a structural ridge line sets the sag angle but that is not exactly right. It sets the ratio of the ridge line length to the length of the hammock fabric (plus any suspension line) that it is attached in parallel with. How you distribute the weight (sitting versus laying and also laying down the center line versus laying on diagonal) while you are in the hammock causes the angle(s) of the fabric to change and this in turn changes how much force is on the ridge line.
    Youngblood AT2000

  9. #19
    Senior Member MikeM's Avatar
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    Completely non-mathematical (but hey, some of us are social sciences types) but I find that I can compensate for a less than ideal set up by the angle and position I assume in the hammock. I just throw up my suspension at arm length, eyeball it and then wiggle around inside the hammock until I feel just right. This style worked for me with the HH Deluxe, and it is working even better with the Black Bird, which seems to be even more forgiving of setup and angle of suspension.

  10. #20
    Senior Member gakayaker's Avatar
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    I am going to hang outside again and try to take some detailed pics to see if someone can show me how I am hanging wrong, because I think my angle is right.
    "Lets Start Today"

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