Required rating of guying system :
Where : F M
r 2
∅ 2
F =
M r 2 sin∅ 2
is the required rating of the guying system , in newtons .
is the bending moment ( torque ) that the tree would apply to a fulcrum at the base if that fulcrum were to support the full leverage of the tree , in Newton metres . ( Calculated above )
is the distance from the base of the tree to the attachment point of the guy line , in metres .
is the angle between the guy line and the lever arm of the stem , in degrees .
Combining these equations gives :
Where : F
F = r 1 × sin∅ 1 r 2 × sin∅ 2
× d 2 × l × 7 , 700
is the required rating of the guying system , in newtons .
r 1 is the distance from the base of the tree to the approximate centre of gravity , in metres .
∅ 1 is the angle between the force ( acting vertically downward ) and the lever arm of the stem , in degrees .
r 2 is the distance from the base of the tree to the attachment point of the guy line , in metres .
∅ 2 is the angle between the guy line and the lever arm of the stem , in degrees .
d is the diameter of the tree just above the root flare , in metres .
L is the length of the tree along its stem from the base of the stem to the tip , in metres .
A ‘ worked example ’ of an imaginary tree rescue is provided on the following page .
An alternative solution where cordage strength is deemed to be insufficient is to use multiple legs of rope . Please see the section on rope elasticity for further details .
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