ITTC-78 corrections applied to the bare-hull frictional coefficient before turning it into delivered power.
Formula
$$ \Delta C_F = \left[ 105 \left( \frac{k_s}{L_\text{pp}} \right)^{1/3} - 0.64 \right] \cdot 10^{-3} $$
$$ C_F^\text{eff} = (C_F + \Delta C_F) \cdot (1 + k_2) $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $C_F$ | Bare-hull ITTC-57 friction coefficient | - | ITTC-57 calculator |
| $\Delta C_F$ | Roughness allowance | - | ITTC-78 |
| $k_s$ | Mean apparent hull roughness (AHR) | m | hull-roughness gauge |
| $L_\text{pp}$ | Length between perpendiculars | m | hydrostatics |
| $1 + k_2$ | Appendage form factor - bulkers 1.10–1.15, Ro-Ro 1.20–1.30, cruise w/ stabilisers up to 1.40 | - | ITTC / CFD |
| $C_F^\text{eff}$ | Effective friction coefficient including roughness and appendages | - | result |
A 30 μm increase in AHR adds roughly 1 % to hull resistance for a typical VLCC.
Sources
- ITTC - Recommended Procedures 7.5-02-03-01.4.
- Townsin - ITTC community paper on average hull roughness.