ITTC STAWAVE-2 closed-form estimate of mean added resistance in head-seas irregular waves. Basis for the EEDI/EEXI weather factor $f_w$.
Formula
$$ R_{AW} = \tfrac{1}{16} \rho g H_{1/3}^2 B \sqrt{\tfrac{B}{L}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $R_{AW}$ | Mean added resistance in irregular waves | kN | result |
| $\rho$ | Sea-water density | kg / m³ | 1025 default |
| $g$ | Gravitational acceleration | m / s² | 9.81 |
| $H_{1/3}$ | Significant wave height | m | sea-state |
| $B$ | Waterline beam | m | hydrostatics |
| $L$ | Waterline length | m | hydrostatics |
Head seas, displacement hull. Accurate to ±20 % for $H_{1/3}/L < 0.04$. Strip-theory or CFD needed for oblique seas or at small wavelength ratios.
Sources
- ITTC - Recommended Procedures 7.5-02-07-02.1.
- IMO Resolution MEPC.212(63) - EEDI weather factor $f_w$.