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Sweating the Fall Things, a Rigging Puzzle

Posted in Puzzle, and Rigging News

Sailors and other rope users are familiar with the process of sweating or swigging up a line: pulling sharply sideways on the fall of a purchase, above the belay point to gain a bit of slack, then quickly transitioning to a downward resolution, so that slack can be taken up at the belay point. The combination of leverage and impact-loading allows you to get more tension than you could by simply pulling down on the line. But the question is: how much more?

In the video below our rigger Julia Briggs is sweating a line in our shop. The line has been set to a starting tension of 200lbs.

Julia weighs 140 lbs.

The line is attached to a load cell that has been set up to read the maximum tension achieved.

So here is the puzzle: how many additional pounds of tension did Julia impose?

Note that Julia makes no effort to take the slack towards the floor; we just wanted to see how much extra tension could be gained. If you have some idea about the result, send it to puzzle@briontoss.com, or write it in the comments section below. Anyone whose guess is within 150 pounds of the actual answer will win a free copy of my new book, Falling, a series of stories about working at heights. You get your choice of an ebook or audiobook version.

Puzzle entry deadline is noon Pacific time, January 5th, 2019, and the winners will be announced on January 7th. Good luck!

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24 Comments

  1. Nels Backstrom
    Nels Backstrom

    672lbs

    December 28, 2018
    |Reply
  2. Brian Tuor
    Brian Tuor

    820 pounds

    December 28, 2018
    |Reply
  3. Ian Duff
    Ian Duff

    420 lbs

    December 28, 2018
    |Reply
  4. I’ll hazard a bit of a guess.
    120lbs x 11 for that load angle, = 1320lbs.
    I’m assuming she’s capable of about her bodyweight (slightly under) in shock load in that situation, but I’ve never actually measured this in real life…

    December 28, 2018
    |Reply
  5. Shock loads are difficult to assess. Let’s assume that Julia is strong (she works for you as a rigger) and gets 75% of her body weight to be effective on the pull, or 105 lb. then the vector sum yields 225 lb…If she manages (thru shock loading) to get 100% of her body weight on the pull (although her feet never left the ground) , then the vector sum yields 244 lb. I’ll split the difference and say 235 lb

    December 28, 2018
    |Reply
  6. Doug stanley
    Doug stanley

    280 additional ft/lb. for the microsecond .

    December 28, 2018
    |Reply
  7. Dev
    Dev

    40 pounds

    December 29, 2018
    |Reply
    • Dev
      Dev

      Sorry, I need to modify my entry of 40# because I didn’t run the video first and saw only the static image. Please put me down for 80 #.

      December 29, 2018
      |Reply
  8. William Crowley
    William Crowley

    Additional 60 pounds.

    December 31, 2018
    |Reply
  9. Heath Morrison
    Heath Morrison

    312 lbs

    January 1, 2019
    |Reply
  10. Been a long time since I did vector stuff and dynamic is for me a wild card – but I will hazard 800 lbs tension on the load cell if it is fast enough reading but based on some calcs many years ago I think I am low –

    January 2, 2019
    |Reply
  11. Elton
    Elton

    401.8lbs

    January 4, 2019
    |Reply
  12. Collin
    Collin

    1012 lbs

    January 4, 2019
    |Reply
  13. Carly P
    Carly P

    670 pounds…

    January 4, 2019
    |Reply
  14. Michael Seng
    Michael Seng

    Assuming:
    A. she generates 75% of her weight in shock load
    B. Estimate that she generates a load angle of 160 degrees
    C. approx. 300% multiplier
    Answer: [200lbs initial + (75%of 140lbs or 105lbs)]*300% or 915lbs

    January 4, 2019
    |Reply
    • Michael Seng
      Michael Seng

      …dang…less the original 200 thus 715lbs.

      January 4, 2019
      |Reply
  15. Ezra
    Ezra

    55lbs

    January 4, 2019
    |Reply
  16. Tyrone
    Tyrone

    800lbs

    January 4, 2019
    |Reply
  17. Larry Best
    Larry Best

    1000 pounds.
    I’d say more but she didn’t move the iron thing on the floor. What is that?

    January 4, 2019
    |Reply
  18. Rich DiMinno
    Rich DiMinno

    750lbs

    January 6, 2019
    |Reply
  19. Savvas Eftychis
    Savvas Eftychis

    350lb total, so the answer would be an additional 150lb
    (Realizing I am late, so out of the contest, for the fun of it)

    January 7, 2019
    |Reply
  20. Matt Adams
    Matt Adams

    1484

    January 8, 2019
    |Reply
  21. Rich Findley
    Rich Findley

    1052.7 pounds extra
    I know too late.
    So what is the answer?

    January 9, 2019
    |Reply

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