Numerical calculation and evaluation of extrapolation coefficients as used in speed-power predictions based on model tests

A comparative analysis has been made of the extrapolation of model tests results using form factors and wake scale effects obtained from both a statistical method and viscous-flow computations. When similar values would be obtained from the numerical approach compared to the statistical method, no change in correlation allowance is needed to predict the same full-scale power. For slender ships, however, this is not the case and the lower form factor and higher wake scale effect from the numerical approach results in a lower correlation allowance in the order of 0.00010. For fuller ships the numerical approach predicts similar form factors but a higher wake scale effect. The ballast draught compared to the design draught is normally extrapolated with an additional correlation allowance but when the numerical extrapolation coefficients are used this additional allowance is reduced, more for slender ships then for fuller ships. A correlation of ballast and design draughts with trial data show an opposite trend where the slender ships need an additional reduction of the correlation allowance in ballast.