Fuel, CO₂ and payback from an in-water hull clean and propeller polish.
Formula
$$ F_\text{saved} = \text{ME}\text{rate} \cdot d \cdot (p\text{hull} + p_\text{prop}) $$
$$ \text{Payback} = \frac{\text{Cost}}{F_\text{saved} / d \cdot \text{Price}_\text{fuel}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $F_\text{saved}$ | Fuel saved over the inter-clean period | t | result |
| $\text{ME}_\text{rate}$ | Main-engine fuel rate (fouled baseline) | t / day | voyage log |
| $d$ | Days between cleanings | d | operating plan |
| $p_\text{hull}$ | Hull-clean recovery fraction (typ. 3–8 %) | fraction | BIMCO IWC data |
| $p_\text{prop}$ | Propeller-polish recovery fraction (typ. 1–3 %) | fraction | BIMCO IWC data |
| $Cost$ | Total service cost | USD | service contract |
| $\text{Price}_\text{fuel}$ | Bunker price for the period | USD / t | bunker index |
| $Payback$ | Days to recover the cost from fuel saved | d | result |
The recovery fraction decays as fouling rebuilds - typical curves halve the first-day savings within 4–6 weeks. Cold water slows growth, warm tropical calls accelerate it.
Sources
- BIMCO - Industry Standard on In-Water Cleaning.
- IMO MEPC.378(80) - 2023 biofouling guidelines.