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  1. #1
    Senior Member DemostiX's Avatar
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    Jan 2011
    Like Lewis & Clark: Wintrin' o/t Columbia again: PDX
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    Where is the local load on the tree?

    After spending some time on knots, edges, and the localized burden they put on ropes, I wondered about the local load on trees. (I guess "tree-hugger" has different and uncertain meanings here.)

    With ropes, investigators have looked at just where the rope breaks; I haven't gotten as far as to find the reports of engineers and materials scientists who have measured strain within the rope at different points. But it is intuitive to rope users that some knots and edges are tougher on the rope than others.

    Now, with trees: We all have the experience of preferring loaded straps on our shoulders to loaded thin cords. Straps distribute load and cut less. So, we load trees less with straps than with line. But, exactly where is the load put on the tree by a loaded hammock? It would seem that would depend on the adhesion of the line or straps to the tree. If there is adhesion, all the load might be just behind points of tangency of line or straps to the tree.I dunno what that means in real usage.

    So, are there some prof or amateur engineers with knowledge or insight on this? And some tree experts who know something about the pressure below which the trees we'd hang from cannot be said to have even detected the hammock load after the hammock is taken down?

    Finally, for now, is there a guideline somewhere here, for good hygiene on this issue: pressure on the tree bark,-- based on science and engineering analysis?

  2. #2

    Join Date
    Jan 2011
    South Central IN
    WBRR, Lots of DIY
    MacCat; Cloudburst
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    8,137 science or engineering here. Just some edumacated guessing and wild rounding off of numbers.

    Givens...200 lbs person, 1" wide tree strap, 30* angle of hang, circumference of tree = 36".

    Load on tree strap = ~200 lbs.

    Let's say the back 1/3 of the strap takes all (wild rounding) of the load...0.33x 36"x1" = 12sq in.

    200lbs/12sq in = 16.67psi that the tree feels. Bigger tree = lower psi, smaller tree = higher psi.

    When it quits raining, I'll go ask a variety of 36" circumference trees if 16.67psi is OK.

    I once hung on a 5" diameter tree and I think I heard it groan.

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