Enter Winch and Load Details
Example Data Table
This worked example shows how drum fill, efficiency, and safety factor change the final safe working load.
| Parameter | Example Value | Notes |
|---|---|---|
| Application | Lifting | Direct vertical lift with one part of line. |
| Rated first-layer pull | 12 kN | Manufacturer rating at the first rope layer. |
| Drum core / flange / width | 120 mm / 320 mm / 220 mm | Controls storage and layer growth. |
| Rope diameter / length | 10 mm / 45 m | Sets active layer and drum utilization. |
| Efficiency / safety factor | 90% / 3.0 | Reduces gross pull to a working limit. |
| Load weight / dynamic factor | 800 kg / 1.1 | Allows for motion and handling effects. |
| Illustrative result | Governing SWL about 4.0 kN | Enough for the sample lift with margin. |
Formula Used
Turns per layer = floor(Drum width ÷ Rope diameter)
Layer length = Turns per layer × π × Mean layer diameter
Max layers = floor((Flange diameter − Core diameter) ÷ (2 × Rope diameter))
Active pull = First-layer pull × (First-layer mean diameter ÷ Active-layer mean diameter)
Active speed = First-layer speed × (Active-layer mean diameter ÷ First-layer mean diameter)
System pull = Active-layer pull × Parts of line × Efficiency
Winch SWL = System pull ÷ Safety factor
Rope SWL = Rope minimum breaking load ÷ Safety factor
Governing SWL = lower of winch SWL and rope SWL
Lifting: Required pull = Weight force × Dynamic factor
Towing or recovery: Required pull = Weight force × ((Grade + Rolling resistance) ÷ 100) × Dynamic factor
How to Use This Calculator
- Choose the duty type: lifting, towing, or recovery.
- Enter the rated first-layer pull and its unit from the winch datasheet.
- Add drum core diameter, flange diameter, drum width, rope diameter, and installed rope length.
- Set parts of line, mechanical efficiency, and the safety factor used in your procedure.
- Enter the load or vehicle mass, then add slope, rolling resistance, and dynamic factor.
- Optionally enter rope minimum breaking load to let the calculator govern by rope capacity too.
- Press Calculate Capacity to show results above the form.
- Use the CSV or PDF buttons to export the calculated summary.
Frequently Asked Questions
Why does line pull drop as rope layers increase?
Each new layer increases drum radius. With nearly constant winch torque, a larger radius produces less line pull, even though line speed increases.
Why include a safety factor?
A safety factor converts theoretical capacity into a conservative working limit. It helps account for shock, wear, uncertainty, and inspection quality.
What is the difference between winch SWL and rope SWL?
Winch SWL comes from pull, reeving, efficiency, and safety factor. Rope SWL comes from rope breaking strength and safety factor. The lower value should govern.
Should I use lifting mode for every job?
No. Lifting mode assumes the winch supports the full load weight. Towing and recovery use grade and rolling resistance to estimate required pull.
What does parts of line mean?
It is the number of rope segments sharing the load through reeving. More parts increase available pull, but reduce line speed and add losses.
How should I enter rolling resistance?
Use a higher percentage for soft ground, mud, obstacles, poor bearings, or recovery loads. Use a lower percentage for smooth hard surfaces.
Can the calculator replace a rigging plan?
No. It is a planning aid. You still need manufacturer limits, competent supervision, inspection records, and a compliant lifting or recovery procedure.
Why is my installed rope length warning shown?
The warning appears when entered rope length exceeds calculated drum storage. That means the drum may not safely hold the full rope volume.