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  1. #1
    Captn's Avatar
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    Hammock suspension load factor of safety

    When I studied the dark arts of mechanical engineering, way back before recorded history, I can remember many class room discussions centered around factors of safety.

    I thought perhaps a refresher on the principal may be helpful for some of our newer hangers.

    In short, a factor of safety is a number you would multiply your maximum expected load by to account for the unexpected forces of mother nature and the foolishness of your fellow man.


    Before material sciences matured to todays level, it was critical to assume a large enough factor of safety to account for all unknowns.

    In calculating the needed strength of hammock materials and suspension components, a factor of safety is built in to most commercially available materials, except where maximum load numbers are used.

    Differences in assumed factors of safety accounts for the differences between recommended load ratings for commercially available hammocks, such as a GT nano being rated for 250 lbs using 1.27 oz per yard material where a hennessey would consider the max load rating to be about 180. A 300 lb person may get away with using a 1.1 single, for example, by eliminating the safety factor assumed in most designs, however, material strength, sewing processes, etc can vary between two of the same hammocks, making one safe at this load and one not safe. It is generally impossible to see the differences by eye, so push the limits at your own risk.

    It is important to remember that this rating does not equate to comfort level using a different material, which is yet another factor that hammock producers differ on.

    On suspension components however, many times manufactures list the maximum working load of their materials under assumed conditions. Amsteel is
    one such example.

    We, when specifying components for our own hanging system, should always discuss the assumed factor of safety when we discuss our designs between each other.

    I like to use the old tried and true factor of 10 when looking at suspensions, for example. Loading for 250 lbs at a 45 degree hang angle, for example, is calculated by taking 1/2 the load and dividing by the sin of the angle or 176 lbs in each line under static conditions, if you move around or bounce that load can go a lot higher

    Accounting for these unknown conditions of bouncing, moving around, dog or child laying Down with you, etc, by multiplying this number by 10 would give you a minimum suspension component rated strength of 1765 lbs. Go lower at your own risk. Nicks and scratches can significantly degrade component strength as well, so you may want to double this if you are rough on equipment or taking a long hike.

    Good hanging and let's be careful out there.

    http://www.whiteblaze.net/forum/vbg/...iginal=1&c=577
    Last edited by Captn; 02-26-2011 at 10:59.
    Many a good hanging prevents a bad marriage
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  2. #2
    Member zyhano's Avatar
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    Good writeup, tnx,

  3. #3
    Senior Member ofsjason's Avatar
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    This just blew my mind All I know is my hammock was supposed to support 400 pounds and the Carabiners I use each support 21KN. I go 30-45 degree angle sometimes, but sometimes the trees are far apart and there is more tension on the ropes. I'm assuming my 190-200 pounds shouldn't pose a problem regardless of angle with that setup, would that be correct?

  4. #4
    canoebie's Avatar
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    One rule of safety I use is that I don't hang any higher than I am willing to fall.
    Revolution is about the need to re-evolve political, economic and social justice and power back into the hands of the people, preferably through legislation and policies that make human sense. That's what revolution is about. Revolution is not about shootouts.

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  5. #5
    Bubba's Avatar
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    Quote Originally Posted by ofsjason View Post
    This just blew my mind All I know is my hammock was supposed to support 400 pounds and the Carabiners I use each support 21KN. I go 30-45 degree angle sometimes, but sometimes the trees are far apart and there is more tension on the ropes. I'm assuming my 190-200 pounds shouldn't pose a problem regardless of angle with that setup, would that be correct?
    The angle of the suspension is important in that as it approaches horizontal the force on the suspension increases exponentially. At 30 degress the force on each end is equal to your weight IIRC. The farther apart your trees the higher you need to hang your suspension.
    Don't let life get in the way of living.

  6. #6
    Senior Member opie's Avatar
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    Also keep in mind a factor of 10 is used mainly in life support rope and hardware. Having a factor of 4 will suit the hammock community just fine. If you care to have a factor at all.
    I am not a gram weenie. , But Im starting to see the merits!!!

    Kris' Splicing

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  7. #7
    Captn's Avatar
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    Quote Originally Posted by opie View Post
    Also keep in mind a factor of 10 is used mainly in life support rope and hardware. Having a factor of 4 will suit the hammock community just fine. If you care to have a factor at all.
    Good point Opie!

    Choose your factor of safety wisely ... But be aware that it exists. A good example would be 500 lb paracord .... NOT suitable for hanging.
    Many a good hanging prevents a bad marriage
    William Shakespeare


    "Insert witty and intelligent statement here"

  8. #8
    Senior Member lymphocytosis's Avatar
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    Wow. I had no idea the component limit need to be that high.

  9. #9
    Knotty's Avatar
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    Thanks for the writeup Captn. Having also been schooled as a gearhead I'm always thinking about safety factor. I hope your post will encourage others to do same.
    Knotty
    "Don't speak unless it improves the silence." -proverb
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  10. #10
    Captn's Avatar
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    Quote Originally Posted by odds View Post
    The angle of the suspension is important in that as it approaches horizontal the force on the suspension increases exponentially. At 30 degress the force on each end is equal to your weight IIRC. The farther apart your trees the higher you need to hang your suspension.
    At 5 degrees, for example, the tension in the lines will be over 1100 lbs each for a 200 lb person.

    If you've factored in a good factor of safety your setup will handle it.

    BTW ... A 22kn biner will hold 5000lbs, but only once. That number is a maximum.
    Many a good hanging prevents a bad marriage
    William Shakespeare


    "Insert witty and intelligent statement here"

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