Characteristics of rolling with drift in regular beam sea for small hard-chine craft at rest

Abstract

The characteristics of rolling with drift in regular beam sea for a small hard-chine craft at rest is investigated experimentally, and modification of a strip method with Ikeda's roll damping prediction method for hard-chine boat (Ikeda et al., 1990) is proposed. From the comparison between calculated and measured RAO of rolling, it is confirmed that the calculation overestimates roll amplitude at the condition where wave encounter period is shorter than its roll natural period, especially. The reasons of overestimation are investigated and it is confirmed that the coupling viscous roll moment from swaying cannot be ignored for small hard-chine craft for shorter wave period than its roll natural period. Because the roll natural period is shorter than that of a conventional displacement type vessel and its resonant wavelength is short comparing with its breadth, therefore its swaying can't follow orbital motion of wave, then coupling viscous roll moment from swaying becomes significant. Moreover, as another reason of the overestimation, the estimation accuracy of wave exciting roll moment is investigated and it is recommended that the diffraction potential should be solved under strict satisfying the body boundary condition for short wave length (λ/B < 7.0).