Fuel saving from converting anchor-wait time into slower steaming time.
Formula
$$ V_\text{jit} = \frac{D}{D / V_\text{full} + t_\text{wait}} $$
$$ \Delta F = \text{ME}\text{full} \cdot \frac{D / V\text{full}}{24} - \text{ME}\text{full} \cdot \left(\frac{V\text{jit}}{V_\text{full}}\right)^n \cdot \frac{D / V_\text{jit}}{24} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $V_\text{jit}$ | Speed that arrives exactly at the agreed slot | kn | result |
| $V_\text{full}$ | Speed the ship would have steamed without JIT | kn | voyage plan |
| $D$ | Distance to pilot station | nm | voyage plan |
| $t_\text{wait}$ | Anchor/standby time that JIT eliminates | h | port agent / PortCDM |
| $\text{ME}_\text{full}$ | Main-engine daily fuel rate at $V_\text{full}$ | t / day | voyage log |
| $n$ | Speed exponent (≈ 3) | - | Rayleigh cube law |
| $\Delta F$ | Fuel avoided | t | result |
Auxiliary burn hardly changes - it runs whether the ship is at anchor or steaming. CO₂ saving is $\Delta F \cdot C_f$.
Sources
- IMO MEPC.323(74) - voluntary port-ship cooperation.
- GloMEEP / IAPH - Just-in-Time Arrival Guide.