Tagline Wind Force Calculator
Estimate the wind force pushing on a suspended load and the tagline pull a crew needs to control it. Enter the projected sail area, the wind speed and a drag coefficient, and the tool returns the force in newtons and kg-force using the standard F = ½·ρ·Cd·A·v² relationship.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the projected area A (m²) — the flat area of the load presented to the wind, taken from the largest face for a worst case.
- Enter the wind speed v in metres per second (multiply km/h by 0.278 to convert), using the site's forecast or measured gust-adjusted speed.
- Adjust the drag coefficient if needed (1.2 suits a flat plate/panel; leave the default otherwise) and read the wind force and the minimum tagline pull required.
How it works
The dynamic wind force is F = ½ × ρ × Cd × A × v², with air density ρ = 1.225 kg/m³ at sea level. The result is given in newtons and converted to kg-force by dividing by 9.81. The tagline tension needed to hold the load steady is at least this force when the line pulls horizontally; if the tagline runs at an angle φ above horizontal the required tension rises to about F ÷ cos φ, so long, low taglines need substantially more pull.
Worked example
Worked example. A 10 m² panel in a 10 m/s wind with Cd = 1.2 gives F = 0.5 × 1.225 × 1.2 × 10 × 10² = 735 N = 74.92 kgf. A single hand line pulling near horizontal would need to supply at least that much steady force — and more to arrest a gust or if the line is at a shallow angle.
Common mistakes
- Using the load's face-on area at the wrong orientation — wind force scales with the projected area presented to the wind, so a large flat face broadside is the worst case, not the edge-on view.
- Forgetting that force grows with the SQUARE of wind speed: doubling the wind quadruples the force, so a modest breeze on a large panel can quickly exceed what taglines can hold.
- Ignoring the tagline angle — a shallow line needs far more tension (≈ F ÷ cos φ) than the raw wind force, and gusts add dynamic peaks above the steady value.
Frequently asked questions
What wind speed should stop a lift?
Follow the crane manufacturer's stated wind limit for the load — commonly around 9–12 m/s for general lifts, but read the chart, and use a lower limit for large 'sail-area' loads. The in-service wind limit depends on the crane, the load's shape and area, and the rigging. When in doubt, stop and consult the lift plan and a competent person.
Which drag coefficient should I use?
About 1.2 is a common value for a flat plate or panel and is the default here. Long cylinders are lower (≈ 0.7–1.2 depending on Reynolds number), and complex, open or boxy loads vary widely. For lift planning a flat-plate Cd of 1.2 on the largest projected face is a reasonable conservative starting point; use engineered values for critical wind-sensitive lifts.
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