Abstract
Theoretical calculations and model tests of motions and drift forces in beam waves are carried out for two tug boats, a fishing boat and a surveying ship without forward speed. Added masses and damping coefficients are computed by the strip method in which the sectional hydrodynamic forces are calculated by the close-fit method. Wave-exciting forces are, on the other hand, predicted using Kochin's function obtained on the assumption that the ships are slender longitudinally. The viscous effect on roll damping is taken into account by the use of extinction coefficients of free-oscillation tests. The results of the theoretical calculations are compared with the measured data of the four ships. Agreements between calculations and measurements are very good for the amplitudes and the phases of rolling, swaying and heaving motions. As for the drift forces, the calculated values by two approximate methods agree well with the measured ones in a practical point of view.
