Hull Roughness ΔCf (Townsin)
Increment of skin-friction coefficient from measured hull roughness (AHR) using the ITTC-78 Townsin formulation.
ΔCf
0.00036 -
Formula, assumptions, and limits
New-paint hull AHR ~125 µm; 5-year-old self-polishing 200–300 µm; heavily fouled 400 µm+. 50 µm rise adds ~1 % to hull resistance on a typical VLCC.
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| Average hull roughness | µm | gauge measurement | |
| Waterline length | m | particulars | |
| Skin-friction roughness increment | - | result |