Resistance coefficient (CT, CF, CR, CA)

The resistance coefficients nondimensionalize drag by dynamic pressure and wetted surface: C_X = R_X / (0.5 rho V^2 S). The total C_T splits into the frictional C_F (from the ITTC-1957 line), the residuary C_R (wave plus viscous-pressure drag, scaling at equal Froude number), and the correlation allowance C_A added at ship scale to reconcile model prediction with trial results. The ITTC-1978 form-factor variant writes C_T = (1+k) C_F + C_W + C_A, replacing the lumped C_R with a form factor times friction plus a wave coefficient C_W. These coefficients are the working currency of every model-test extrapolation and systematic resistance chart.