Friction-Device Hold Force by Wraps
Hand-side hold force for 1 to 4 wraps on a porta-wrap or lowering bollard by the capstan equation.
Example
You enter
- Load-side tension (lb) 800
- Rope-on-device friction coefficient 0.2
- Wraps to highlight 3
You get
- Hand force, 1 wrap 227.7 lb
- Hand force, 2 wraps 64.8 lb
- Hand force, 3 wraps 18.5 lb
Details, formula, and sources
Hand-side hold force for 1 to 4 wraps on a porta-wrap or lowering bollard by the capstan equation, so one groundie can pick the right wrap count.
hold(n) = load x exp(-mu x n x 2 pi) for n = 1..4 wraps (capstan / Euler-Eytelwein equation). More wraps, exponentially less hand force.
Capstan (Euler-Eytelwein) friction equation and ANSI Z133-2017 by name; first-principles mechanics.
The capstan equation is public physics. ANSI Z133-2017 is a published consensus standard.
Math aid for personal verification. Stop work and consult the qualified person on site if any number does not match the field condition.
Field names used by the API: load_lb, mu, wraps, hold_1_lb, hold_2_lb, hold_3_lb
- Friction coefficient rope-on-device ~0.20 (default; depends on device, rope, glaze, moisture)capstan friction practice