Thrust power from a rigid wing sail or towing kite installation.
Formula
$$ P = C_L \cdot \tfrac{1}{2} \rho_\text{air} V^2 A \cdot V_\text{ship} \cdot f_\text{useful} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $P$ | Time-average thrust power contributed to the ship | kW | result |
| $C_L$ | Effective lift coefficient - wing 1.0–1.4, kite 0.8 time-averaged | - | CFD / wind-tunnel |
| $\rho_\text{air}$ | Air density | kg / m³ | 1.225 |
| $V$ | Apparent wind speed | m / s | anemometer / route data |
| $A$ | Sail or kite projected area | m² | design |
| $V_\text{ship}$ | Ship speed | m / s | operating profile |
| $f_\text{useful}$ | Share of voyage hours with useful wind angle | fraction | route climatology |
Wing sails (Oceanbird, bound-to-ship) work best with steady side winds. Kites (SkySails, free-flying on a tether) work best in following or quartering trade winds and give a larger effective sail area per installed cost.
Sources
- Oceanbird Wallenius - wind-powered RoRo concept.
- SkySails Marine - towing kite systems.
- IMO Resolution MEPC.1/Circ.815 - innovative energy-efficient technologies.