Calculating deflection forces
There are several methods to calculate the forces generated when a tensioned line is deflected by a load , however they are of limited use during a tree rescue . Anchor points are rarely level , and the load is rarely applied equidistant from the anchors .
The methods below are provided to assist with comparison of systems during training or whiteboard system design . For the purposes of this manual , there is no need to calculate the forces applied ; the ‘ rules of thumb ’ are sufficient .
Calculating deflection forces method 1
Where a load f is suspended between two points at equal height , equidistant from either point , the magnitude of the force F on each point is given by :
F =
Where : f 2sin∅
F is the force applied to each anchor , f is the load applied to deflect the rope , and Ø is the angle between the rope at the anchor and an imaginary horizontal line between the two anchors
This can also be written as :
F = f√ ( x2 + y 2 ) 2x
Where :
F is the force applied to each anchor , f is the load applied to deflect the rope , x is the vertical distance that the rope has deflected below the horizontal ( sag ), and y is the horizontal distance of the load from each point .
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