Tree Work
Dynamic Load Calculator
A 500 lb log dropped just 3 feet onto a tight rigging line can generate over 5,000 lb of peak force. Enter the static weight, drop distance, and rope length to estimate the actual dynamic load.
Peak dynamic force (lb)
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- Fall factor
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- Shock multiplier
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- Required MBS at 5:1 DF (lb)
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FAQ
What is fall factor? +
Free-fall distance divided by total rope in the system. A fall factor of 1 (rope catches at the same height it left) is severe; FF of 0.3 or less is generally considered "controlled."
Why does rope stretch matter? +
A stretchy rope absorbs energy over a longer time, lowering peak force. Low-stretch lines (Dyneema, wire core) can shock-load the anchor with 5-10x the static weight. Nylon was the original "shock absorber" rope in arborist work for this reason.
How conservative are these numbers? +
This is an engineering estimate. Real-world peak loads also depend on knot slip, friction at the rigging point, and how the load fell. Always size the system with a 5:1 design factor on the peak — not the static — load.