On the Accuracy of Wave Pattern Resistance Determination by the Longitudinal Cut Method

In the present work a careful study has been performed on the main error sources in the wave resistance determination by the longitudinal cut method. The experimental data obtained at the Italian Ship Model Basin (wave profiles generated by the steady motion of the Series 60) have been analysed and the relative measurement confidence intervals have been computed. The corresponding confidence interval has been next obtained for the wave resistance coefficient within the range of Froude numbers examined (.225 ÷ .350), taking into account the error band related to the wave profiles in the application of the longitudinal cut method: the 95% confidence interval shows a rather narrow band and the comparison with the numerical wave resistance as well as with experimental data available in the literature shows a satisfactory agreement. Moreover, the errors related to the truncation of the wave profile, typical of the longitudinal cut method, have been estimated by systematic tests performed by means of a numerical approach, which allows one to compare the wave resistance evaluated by the longitudinal cut method (applied in this case to the computed wave pattern) with the value obtained by pressure integration on the hull. As a result, in a sufficiently wide tank (b > 12m) the longitudinal cut method can be applied without introducing any severe limitation for the model length.