Page 3 of 5 FirstFirst 12345 LastLast
Results 21 to 30 of 43
  1. #21
    Senior Member NCPatrick's Avatar
    Join Date
    Oct 2006
    Location
    Winston-Salem, NC
    Hammock
    WB Traveler
    Tarp
    Custom OES tarp
    Insulation
    JRB Down UQ/TQ
    Suspension
    Whoopie slings
    Posts
    9,041
    Images
    40
    Quote Originally Posted by FLRider View Post

    Bolded for emphasis. That's the worst pun I've read all month. By rights, I should flee screaming into the night, holding my nose...
    Thank you. Thank you very much. I'm here all night...


    "Civilization is the limitless multiplication of unnecessary necessities."
    - Mark Twain
    I go to nature to be soothed and healed, and to have my senses put in order.
    - John Burroughs

  2. #22
    krugd's Avatar
    Join Date
    Feb 2009
    Location
    Northern Ky
    Hammock
    Wannabee- BB-like hammock
    Tarp
    8 x 10 sil tarp
    Insulation
    DIY tq, Phoenix UQ
    Suspension
    whoopie slings and
    Posts
    697
    Quote Originally Posted by GrizzlyAdams View Post
    someone 'round here good at Mathematica?
    You rang?


    Quote Originally Posted by GrizzlyAdams View Post
    which the quick-witted but never-the-less kind among the gentle readership here have not pointed out. The blunder-headed mistake.

    For you see, the slope of the line at 30 degrees is not PI/6, it is of course the length of the opposite side of the triangle over the length of the adjacent side, known in the biz as "tangent". Substituting tan(PI/6) in the equations where once PI/6 stood as an object lesson in the wisdom of not posting hastily, and re-doing the calculations gives the ratio of interest as....wait for it....
    0.83 with some other digits that aren't 33333, but I'm doing numerical integration here, and probably more to the point, the parabola ain't a catenary curve.
    Hmm.. I worked this out for both the catenary and the parabola and am getting no where near 83% - closer to 95%. In fact Tan[Pi/6] is very close to Pi/6, so I don't see why your result would change so much. But maybe I've made a blunder somewhere?

    For those who love the power of calculus I've attached a PDF of the Mathematica notebook I used.
    Attached Files Attached Files
    --Don---

    May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view. May your mountains rise into and above the clouds. - Ed Abbey

  3. #23
    Senior Member Shnick's Avatar
    Join Date
    Mar 2012
    Location
    South Georgia (not by choice)
    Hammock
    ENO Doublenest
    Tarp
    Wilderness Tadpole
    Insulation
    Not in Georgia...
    Suspension
    Whoopies!
    Posts
    408
    Images
    16
    Oh God, not again...



    Shnick
    ...Levitate me
    - Pixies

  4. #24
    GrizzlyAdams's Avatar
    Join Date
    Apr 2007
    Location
    Illinois
    Hammock
    DIY Bridge, v0.n, where n is large
    Tarp
    depends on season
    Insulation
    DIY UQ
    Posts
    4,628
    Images
    564
    Quote Originally Posted by krugd View Post
    You rang?




    Hmm.. I worked this out for both the catenary and the parabola and am getting no where near 83% - closer to 95%. In fact Tan[Pi/6] is very close to Pi/6, so I don't see why your result would change so much. But maybe I've made a blunder somewhere?

    For those who love the power of calculus I've attached a PDF of the Mathematica notebook I used.
    Hi Don! The more the merrier...

    Before you posted this I found formulas for the arclength and tangent angle of the cat curve, which let me gin up something in Perl to solve numerically for the ratio of interest....and it was close to 95%.

    On seeing this I went back to my equations and see the problem,
    a = tan(PI/6)/L, not a = 2*tan(PI/6)/L. With that fix the parabolic approximation comes in with an answer at 95% too. So...the mystery of the origin of 83% remains.

    NCPatrick---that is an EXCELLENT cartoon. A number of fundamental equations in there I recognize, and a bunch that I don't. This is T-shirt material....!
    Grizz
    (alias ProfessorHammock on youtube)

  5. #25
    Redoleary's Avatar
    Join Date
    Feb 2009
    Location
    Pennfield Twp, MI
    Hammock
    DIY gathered end
    Tarp
    Hinterland gear
    Insulation
    down bag
    Suspension
    strap & E.T.'s
    Posts
    3,182
    Images
    69
    I did not think that the 30 angle was specifically related to the 83% rule. I thought the 30 bit came from the force on the suspension, once you get much past 40-sum degrees the load almost exponentially increases. I of course can't find any chart to back that up, and I'm no mathlete so I can't prove it out mathematically either.
    Good luck,
    RED

    My Youtube Channel

    Deep peace of the running wave to you.
    Deep peace of the flowing air to you.
    Deep peace of the quiet earth to you.
    Deep peace of the shining stars to you.
    Deep peace without end to you.
    adapted from - ancient gaelic runes

  6. #26
    New Member
    Join Date
    Apr 2012
    Location
    Dallas, TX
    Posts
    29
    Any chance it's just empirical knowledge. As people hung the hammocks they noticed were it was most comfortable and so came up with the ridge line. After the fact somebody decided to build a new hammock of different length, measured the ridge line, measured the hammock length, bam found a ratio and that ratio worked as hammock length changed.

    I'm from the TLAR school "That looks about right" although it's probably the TFAR "That feels about right" school which created this rule.

  7. #27
    Ramblinrev's Avatar
    Join Date
    Apr 2008
    Location
    Milton, PA
    Hammock
    Hennessey Explorer Ultralight
    Tarp
    Hennessey Hex
    Insulation
    HH Super Shelter
    Suspension
    ring buckle
    Posts
    7,294
    Images
    101
    Quote Originally Posted by Shnick View Post
    Oh God, not again...



    Shnick
    It's been a while since we've had a good mathlete Olympics....
    I may be slow... But I sure am gimpy.

    "Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
    Mrs. Loftus to Huck Finn

    We Don't Sew... We Make Gear! video series

    Important thread injector guidelines especially for Newbies

    Bobbin Tension - A Personal Viewpoint

  8. #28
    krugd's Avatar
    Join Date
    Feb 2009
    Location
    Northern Ky
    Hammock
    Wannabee- BB-like hammock
    Tarp
    8 x 10 sil tarp
    Insulation
    DIY tq, Phoenix UQ
    Suspension
    whoopie slings and
    Posts
    697
    Quote Originally Posted by Shnick View Post
    Oh God, not again...



    Shnick
    You sound like some of my students. Don't worry, no quiz this week.

    Quote Originally Posted by BBenski View Post
    Any chance it's just empirical knowledge. As people hung the hammocks they noticed were it was most comfortable and so came up with the ridge line. After the fact somebody decided to build a new hammock of different length, measured the ridge line, measured the hammock length, bam found a ratio and that ratio worked as hammock length changed.

    I'm from the TLAR school "That looks about right" although it's probably the TFAR "That feels about right" school which created this rule.
    I think that's probably it. Someone dialed in their own hammock and then started passing around the number. Though 83% sounds a bit too exact for anything empirical.

    Patrick - I too like the graphic. May have to make it part of one of my class websites. Students just love it when I bring up a graphic they've been doing their best to ignore and show them that its an integral (sorry - pun NOT intended) part of the course.
    --Don---

    May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view. May your mountains rise into and above the clouds. - Ed Abbey

  9. #29
    Senior Member DemostiX's Avatar
    Join Date
    Jan 2011
    Location
    Like Lewis & Clark: Wintrin' o/t Columbia again: PDX
    Hammock
    Clark w 2QZQ mod,Tropical, NX;Nano
    Tarp
    Clark micro
    Insulation
    Major down
    Suspension
    7/64 SK75 +strap
    Posts
    2,325
    Images
    13
    Won't any old coot sure he's as smart as back then check the records on this?

    Is Hennessy really the originator of the guidance? Or is that a just so story,too.

    Are you sure that 83.33% is not a mis-transcription, a copy error of 86.6%, .866 being the cosine of a 30 degree angle. (Sit in the center of a 100" hammock stretching between trees 86.6" apart and the hang angle will be 30 degrees) and the ridgeline barely taut.)

    [A big BTW is that much as folks like to refer to cat cuts and the bridge hammock (BH) as being catenary curve based, according to references in raifenuke's comment, a suspension bridge is better modeled as a simpler parabola, what with its very heavy deck, and so certainly for the same reasons --negligible weight of the bridge hammock compared to even Grizz's lightest beneficiaries -- should bridge hammocks. All well covered in prior notes here?]
    Last edited by DemostiX; 04-11-2012 at 18:05. Reason: cat vs parabola

  10. #30
    Senior Member Shnick's Avatar
    Join Date
    Mar 2012
    Location
    South Georgia (not by choice)
    Hammock
    ENO Doublenest
    Tarp
    Wilderness Tadpole
    Insulation
    Not in Georgia...
    Suspension
    Whoopies!
    Posts
    408
    Images
    16
    In the military, no one knows WHY we are told we have 9 seconds to put our gas mask on, WE JUST DO IT...

    Could the same simple solution apply here as well? It's 83% just 'cause?

    I'm dropping this class, sorry guys...
    A very confused Shnick
    ...Levitate me
    - Pixies

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
  •