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Originally Posted by PTC  I dont know of any literature explaining the forces involed in this type of set up. Does the 5x the load come from pretensioning the line with a drum? |
Yes, it all depends on the angle of the rope, less tension means the ropes angle changes.
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Originally Posted by PTC If so, does this mean that if you use a line that is only pretentioned by hand that the forces on the tie in points would be closer to double your weight? |
Closer yes, but still more than double.
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Originally Posted by PTC Similar forces to a set up with climing line runninig through a pulley that is being held up by another rope that runs over a branch and is tied off at the base? |
No, different concept, that has force multipliers in the same line, here we have force multipliers depending on the angle of the line.
When a crane has two chians to lift a beam, as the angle of the chains attached to the beam changes so does the force on the each chain. At 120 degrees the chains each experience the same weight as the load, you'll never see a crane go past that either.
Here's an easy experiment for you.
Got a good spring scale, maybe 25kg one?
Get a rope and tie it to your fence at say middle rail 1m ht.
Tie say a 3kg to 5kg weight on the rope. On the other end of the rope (weight in the middle) have the spring scale.
Slowly lift the weight, starting straight up, like double rope. Note the weight on the scale.
Now start pulling away from the fence and have the weight on the rope inline with a tight rope, check the scale. 5x
