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Originally Posted by PTC  Thanks Ekka, good explanation 
So if we took your diagram, extended the rope from the blue scales over a branch and tie it of at the ground, can we calculate the load on the branch (assuming we know the load at the scales) or do we need to factor in the angle of the rope again?
apologies for lack of diagrams |
Angles always make a difference when there's loads applied.
You can have a tight rope horizontal across say a river, have say 500kg weight hanging in middle, like a flat speed line. The amount of force or weight on each end of that rope is the same, however if the rope was the other extreme which is vertical all that 500kg of load would be on the top knot.
As the angle of the line changes so does the force at either end.
If a horizontal rope was pretensioned with say 250kg of force, then ole mate who weighs 100kg is added hanging in the middle of that rope, what force would be on each end?
750kg
You already have 250kg of tension, ole mate is going to weigh 5x due to the factor here (roughly) so ole mate is adding 500kg of force onto the ends of the rope. I do say roughly coz the rope does get a slight dip in it when load is added.
This is part of the reason why you shouldn't dump loads onto a tensioned speed line.
Here's a good simulator, drag the blue diamond along to 100kn and look at the numbers on the end, and that is with a 30 degree deflection and no pre tension.
TAG : Tyrolean traverse load simulator