Air-drag force on a ship’s transverse above-water area.
Formula
$$ R_\text{wind} = \tfrac{1}{2} \rho_\text{air} V_\text{rel}^2 A_T C_X $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $R_\text{wind}$ | Wind resistance force | kN | result |
| $\rho_\text{air}$ | Air density (ISA sea-level) | kg / m³ | 1.225 default |
| $V_\text{rel}$ | Relative wind speed (true wind vectorially added to ship speed) | m / s | anemometer / voyage plan |
| $A_T$ | Transverse above-water projected area | m² | GA plan / OCIMF table |
| $C_X$ | Wind-drag coefficient - tanker 0.55, bulker 0.60, container laden 0.70, Ro-Pax 0.80+ | - | Blendermann / OCIMF |
For EEDI, the weather factor $f_w$ multiplies the expected wind + wave resistance in a standard reference sea (Beaufort 6, $H_{1/3} = 3.0$ m). Wind contribution scales with $V_\text{rel}^2$, so a 4 Bft vs 6 Bft sea more than doubles the air-drag term.
Sources
- ITTC - Recommended Procedures 7.5-04-01-01.1 (wind resistance).
- Blendermann - Parameter identification of wind loads on ships (1994).
- OCIMF - Prediction of Wind and Current Loads on VLCCs.