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  1. #1
    Senior Member Curt's Avatar
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    Ridgeline Physics

    Good morning!

    I'm trying to figure out the physics of the different loads that hammocks create. One of the things I'm scratching my head about is the ridgeline vs. the tree connection.

    It seems pretty common to not go less than 900+ lbs on the tree suspension straps. Most around here go 1200+ based on posts I've read. But the structural ridgeline numbers are MUCH lower - some folks using as little as 200 lbs. Is it really under that much less stress?? Anybody have the math on this so I can play with some numbers?

    On another note, what kind of rating would be needed on a combined structural ridgeline/tree connection line? I'm talking about a straight line between two trees, likely under a lot of horizontal tension to get it tight, then hanging the hammock from that - pretty much a clothesline setup.

    Thanks much! I'm having fun tinkering with different setups and wouldn't be having the great time I am without all the fantastic input of folks in this forum!

    -Curt

  2. #2
    Senior Member blackbishop351's Avatar
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    There have been a couple threads in which the suspension and ridgeline tensions have been worked out. Yes, with "commonly used" sag angles, the ridgeline is under much less tension than the suspension. Using a continuous rigeline/suspension wouldn't change the way the forces are distributed, but because the material used would have to take the higher suspension forces along its entire length, you might well end up with more weight than you need that way.
    "Physics is the only true science. All else is stamp collecting." - J. J. Thompson

  3. #3
    try this experiment, have someone else lay in your hammock to weight it, attach one rope to each suspension point, where the suspension rope attaches to the fabric, like you would attach a external ridgeline over the netting, now pull them together so they meet in the middle of the hammock above the netting. cross your arms and pull, i was able to pull the ends several inches closer together this way just by hand, in a sense you are just making the hammock "taco" a bit from end to end. it doesn't take nearly as much force as you might think. here is what determines how much. the ridgeline will always be horizontal, it is the suspension lines that will vary. if the suspension lines were hanging straight down, the ridgeline would be directly perpendicular to the suspension lines and thus the less force needed to pull the ends closer together.in contrast, if the suspension lines are cranked down so they are almost completly horizontal to the ground, the ridgeline is no longer pulling anywhere close to perpendicular to the suspension line, and more force is needed to pull them in this direction.in reality, this worse case scenario seems to be hard to create, because even if the suspension lines are horizontal to the ground during setup, once weighted, they will not stay that way, and will be angled down toward the ground, so that the ridgeline is at least partially perpendicular to them, another thing i just realized 2 seconds ago.(so i may be wrong) it seems like the longer the suspension lines,the less force needed to pull the ends a fixed amount closer together, the shorter they are, the more force needed, maybe one of the math guys knows if this is true or not. hope this helps, i know all the equations on these subjects can be hard to follow, i think tangents and cosines is where i gave up on math, and i don't even try to understand the mathematical statistics side of it anymore, just makes me more confused. lol. hope this helps...Brandon

  4. #4
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by Curt View Post
    Good morning!

    I'm trying to figure out the physics of the different loads that hammocks create. One of the things I'm scratching my head about is the ridgeline vs. the tree connection.

    It seems pretty common to not go less than 900+ lbs on the tree suspension straps. Most around here go 1200+ based on posts I've read. But the structural ridgeline numbers are MUCH lower - some folks using as little as 200 lbs. Is it really under that much less stress?? Anybody have the math on this so I can play with some numbers?

    On another note, what kind of rating would be needed on a combined structural ridgeline/tree connection line? I'm talking about a straight line between two trees, likely under a lot of horizontal tension to get it tight, then hanging the hammock from that - pretty much a clothesline setup.

    Thanks much! I'm having fun tinkering with different setups and wouldn't be having the great time I am without all the fantastic input of folks in this forum!

    -Curt
    TeeDee gave the definitively analysis here. You got an equation, plug and chug those numbers to your heart's content.

    I later chimed in with an anal retentive explanation of the formula, because I didn't understand where it had come from. TeeDee has a more intuitive approach to about this stuff than I do.

    Grizz

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