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
Checked against published worked examples from: Capstan (Euler-Eytelwein) / ANSI Z133-2017.
Details, formula, and sources
ScopeHand-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.
Formula or tablehold(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.
Source and editionCapstan (Euler-Eytelwein) friction equation and ANSI Z133-2017 by name; first-principles mechanics.
Free accessThe capstan equation is public physics. ANSI Z133-2017 is a published consensus standard.
What governsMath aid for personal verification. Stop work and consult the qualified person on site if any number does not match the field condition.
API field namesload_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