Friction line (ITTC-57)

The ITTC 1957 model-ship correlation line gives the frictional resistance coefficient as $C_F = 0.075 / (\log_{10} Re - 2)^2$. It is not a pure flat-plate friction line but a correlation line carrying a small built-in form allowance, adopted so model frictional resistance can be subtracted and the residuary part scaled by Froude’s law. It underpins the ITTC-78 powering extrapolation; the full-scale frictional component uses the same formula at ship Reynolds number.