Net fuel saving from optimised track selection through time-varying wind/wave/current, less the extra distance accepted.
Formula
$$ F_\text{routed} = F_\text{base} \cdot (1 - p_\text{save}) \cdot (1 + p_\text{extra}) $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $F_\text{base}$ | Fuel on the rhumb/great-circle route at reference speed | t | voyage plan |
| $F_\text{routed}$ | Fuel on the optimised route | t | result |
| $p_\text{save}$ | Fractional fuel reduction from avoiding weather | fraction | 2–5 % trans-ocean, 4–7 % monsoon |
| $p_\text{extra}$ | Fractional extra distance accepted | fraction | 1–3 % typical |
Break-even: $p_\text{save} > p_\text{extra} / (1 + p_\text{extra})$. A 4 % saving comfortably justifies a 2 % detour.
Sources
- StormGeo - Ship Routing Services.
- ECMWF - high-resolution atmospheric model.
- IMO Resolution MEPC.282(70) - SEEMP weather-routing guidance.