Page 1 of 5 123 ... LastLast
Results 1 to 10 of 48
  1. #1

    Max weight/line stress

    Not sure where to put this

    I just finished a rigging class(navy) and one of the subjects was sling angle stress and the weight effects of a load when the angles are changed.
    SO for all who always wanted to know what type/how much of load they are putting on there tree huggers and hammock line, here it is:
    ref: NAVFAC P-307
    when a sling angle is reduced to 0 degree the stress is increased by a factor of 13
    when the angle is at 5 degrees the stress is increased by a factor of 11.49

    so if I tighten my hammock to zero degrees and then lay in it, the lines are about 5 degrees. Now take my weight of 200 lbs times the 11.49 and you have
    2298lbs ON EACH side.
    So, why does the 1400lb line hold????
    Answer, It has a built in safety factor, like 6 to 1 And the load(weight) I place on the hammock is slowly added. (don't jump into your hammock)

    And for all those who want to tie a knot in your line, This will reduce the line strenght by 50% (the HH Knot is really a bend/lashing and not a Knot)

    There is alot more info on this, If any one wants to 'really' know.

    Thanks
    Sandy B

  2. #2
    Senior Member Just Jeff's Avatar
    Join Date
    Oct 2006
    Location
    Charlottesville, VA
    Hammock
    Blackbird
    Tarp
    MacCat Standard
    Insulation
    Winter Yeti, MWUQ4
    Suspension
    Whoopie Slings
    Posts
    8,012
    Images
    32
    I doubt your hammock is really at 5 degrees when you're laying in it...probably at least 15-20. But you're right about everything else...that's why I ended up on meh arse when I used 550 cord...
    “Republics are created by the virtue, public spirit, and intelligence of the citizens. They fall when the wise are banished from the public councils because they dare to be honest, and the profligate are rewarded because they flatter the people, in order to betray them.” ~Judge Joseph Story

    - My site: http://www.tothewoods.net/
    - Designer, Jeff's Gear Hammock / Pack Cover by JRB

    IMPOSSIBLE JUST TAKES LONGER

  3. #3
    Just Jeff,
    There is a chart for most angles, I only wrote down the 0 and 5 degree, I'll get a copy to post here.
    Thanks
    Sandy B

  4. #4
    Senior Member blackbishop351's Avatar
    Join Date
    Oct 2006
    Location
    Greensboro, NC
    Hammock
    Homemade Speer-type
    Tarp
    BlackCat
    Insulation
    Potomac UQ
    Posts
    1,564
    Images
    59
    Quote Originally Posted by Just Jeff View Post
    I doubt your hammock is really at 5 degrees when you're laying in it...probably at least 15-20. But you're right about everything else...that's why I ended up on meh arse when I used 550 cord...
    Yeah mine's probably at about 5* before I get in it - and that's as tight as I can make it (my HH, anyway). Probably at least 20-25* when I'm in it, maybe more.
    "Physics is the only true science. All else is stamp collecting." - J. J. Thompson

  5. #5
    Senior Member
    Join Date
    Oct 2006
    Location
    New Orleans, LA
    Posts
    3,565
    Images
    57
    Quote Originally Posted by Sandy B View Post
    Not sure where to put this

    I just finished a rigging class(navy) and one of the subjects was sling angle stress and the weight effects of a load when the angles are changed.
    SO for all who always wanted to know what type/how much of load they are putting on there tree huggers and hammock line, here it is:
    ref: NAVFAC P-307
    when a sling angle is reduced to 0 degree the stress is increased by a factor of 13
    when the angle is at 5 degrees the stress is increased by a factor of 11.49

    so if I tighten my hammock to zero degrees and then lay in it, the lines are about 5 degrees. Now take my weight of 200 lbs times the 11.49 and you have
    2298lbs ON EACH side.
    So, why does the 1400lb line hold????
    Answer, It has a built in safety factor, like 6 to 1 And the load(weight) I place on the hammock is slowly added. (don't jump into your hammock)

    And for all those who want to tie a knot in your line, This will reduce the line strenght by 50% (the HH Knot is really a bend/lashing and not a Knot)

    There is alot more info on this, If any one wants to 'really' know.

    Thanks
    Sandy B
    I would say they hold because you are putting half your weight on each support, or 100lbs converted to 1144lbs of stress at 0 degrees. Well below the 1400 lbs breaking strength and any safty factor built in.

    An interesting point on the knots. I have heard for a long time and in different places that knots reduce rope strength by 50%.

    An interesting question would be which lashing can we use in place of the knots in our setups? Also how much do lashing effect the strength of the rope? I am thinking it is some, but how much.


    Quote Originally Posted by blackbishop351 View Post
    Yeah mine's probably at about 5* before I get in it - and that's as tight as I can make it (my HH, anyway). Probably at least 20-25* when I'm in it, maybe more.

    That's about where I am. No matter how taught I start, I usually end up around 20 degrees.

    BTW, I don't usually gentily get in. I just sit in and swing around. You should see what I do to test it for the first hang.
    Is that too much to ask? Girls with frikkin' lasers on their heads?
    The hanger formly known as "hammock engineer".

  6. #6
    Senior Member blackbishop351's Avatar
    Join Date
    Oct 2006
    Location
    Greensboro, NC
    Hammock
    Homemade Speer-type
    Tarp
    BlackCat
    Insulation
    Potomac UQ
    Posts
    1,564
    Images
    59
    Quote Originally Posted by hammock engineer View Post
    You should see what I do to test it for the first hang.
    Do I detect a patented 'Superman Entry Method' in the works?
    "Physics is the only true science. All else is stamp collecting." - J. J. Thompson

  7. #7
    Hammock Engineer,
    Those factors are based with two slings lifting the load. The math is the stress on EACH leg (or side) of a sling. When a load is rasied with the slings at 90 degrees to the load both slings would lift 1/2 the weight, as the angle is changed by 5 degrees the load lifted starts to increase.
    I have put a dynometer(sp) on one leg of a sling and this math works, Maybe I'll take my hammock to work and check it out.

    Sandy B

  8. #8
    slowhike's Avatar
    Join Date
    Oct 2006
    Location
    Winston-Salem, NC
    Hammock
    DIY, gathered end , w/ spreader
    Tarp
    DIY w/ pull-outs
    Insulation
    DAM/ HG Incubator
    Suspension
    Webbing & rings
    Posts
    10,596
    Images
    319
    Quote Originally Posted by hammock engineer View Post
    .
    An interesting point on the knots. I have heard for a long time and in different places that knots reduce rope strength by 50%.
    . .)
    from what i read, some knots take away more than others. that would be useful info to look into.
    don`t leave the CREATOR out of the creation!

  9. #9
    Senior Member
    Join Date
    Oct 2006
    Location
    New Orleans, LA
    Posts
    3,565
    Images
    57
    Quote Originally Posted by Sandy B View Post
    Hammock Engineer,
    Those factors are based with two slings lifting the load. The math is the stress on EACH leg (or side) of a sling. When a load is rasied with the slings at 90 degrees to the load both slings would lift 1/2 the weight, as the angle is changed by 5 degrees the load lifted starts to increase.
    I have put a dynometer(sp) on one leg of a sling and this math works, Maybe I'll take my hammock to work and check it out.

    Sandy B
    That's something I would like to see the results from. It would be interesting so see what the real world data is at different angles. I know and trust the math behind it, but I always like physical data better.
    Is that too much to ask? Girls with frikkin' lasers on their heads?
    The hanger formly known as "hammock engineer".

  10. #10
    Senior Member lvleph's Avatar
    Join Date
    Feb 2007
    Location
    RVA
    Posts
    717
    Images
    9
    Quote Originally Posted by hammock engineer View Post
    That's something I would like to see the results from. It would be interesting so see what the real world data is at different angles. I know and trust the math behind it, but I always like physical data better.
    The real world data is almost always different than theoretical. There are almost always losses unaccounted for.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •