The recommended height difference between the beginning and ending of a zip line is 6% of the zip line’s total length.
Example: A 100ft zip line will have a 6ft height difference. A 200ft zip line will have a 12ft height difference.
How to measure for sloped ground:
From the beginning anchor, look through a sight level to the ending anchor. When the sight bubble aligns with the center line in the sight have a second person mark the level point on the end anchor. Subtract (A) the height of the sight level off the ground from (B) the height of the end anchor’s point off the ground to find (C) the elevation change of the ground. B-A=C
Factor in the elevation change to calculate beginning and end anchor heights.
No proper zip line is piano-string tight. The natural sag in the cable contributes to the acceleration of the ride. When a test weight is on the line, it ideally should sag below the end anchor about 2% of the zip line’s total length.
A 7ft clearance off the ground from the cable’s lowest point is recommended.
For a 100ft zip line, the end of the cable would anchor 2ft higher than the lowest point of the cable when a test weight is on the line. The minimum height on the ending anchor would be 9ft to accommodate 7ft ground clearance.
Tree anchors must be at least 12” thick in diameter. Only healthy, sturdy trees are suitable as anchors. Never attach cable to trees with excessive decay, cracks, exposed roots, diseases, excessive lean, lightning damage or poor tree architecture. Free-standing poles (without guy-wires) must be 12” diameter, minimum. Poles must be sunk into ground at least 4’ or 2’ plus 10% of the pole’s height, whichever is greater.
Eyebolts used to terminate a zip line to a pole or tree must penetrate anchor entirely in order to be secured with a washer and nut.
If the trolley does not mount freely on the cable, be sure to thread the cable through the trolley before terminating the zip line to the anchor.
Otherwise, the trolley wheels can be un-bolted to allow the trolley to assemble onto the cable.
For cable lengths up to 100’, create a loop at the end with a cable clamp. Wrap around the anchor and loosely clamp the intersecting cable. Pull loop to tension line, then secure cable with three clamps.
If the cable is too difficult to tension by hand, hitch the loop to a vehicle or winch. A winch and cable grab combination is most practical, requiring no cable loop.
U-bolt portion of clamps should press against dead end of cable. Space clamps 1-2 inches apart. Tighten clamps with a wrench to “moderately past snug” (≈ 30 Ft. Lbs).
Turnbuckles are used to adjust cable tension. While major adjustments require a winch and cable grab, the turnbuckles are useful for fine tuning.
It is recommended to back up every turnbuckle with a cable and clamps.
Do not chain link carabiners, only link attachments directly to trolley. Multiple carabiners can link to trolley . Do not put more than one attachment in a carabiner.