An investigation of different methods for the prevention of parametric rolling

The parametric rolling of modern containerships is emerging as a serious problem, to the extent that its effects warrant a study into its prevention. In light of this, two methods for reduction of parametric rolling are proposed and examined by physical model experiments. The first is a sponson attached to the side of a ship, the purpose being to decrease the rate of change of the rollrestoring moment. The second is an antirolling tank to increase roll damping. By conducting free-running model experiments for a 6600-TEU post-Panamax container ship with sponsons under typical parametric rolling conditions, it was found that the sponsons could decrease the magnitude of parametric rolling. The antirolling tank could prevent parametric rolling completely in certain conditions, even in severe head seas. Using the damping coefficients from experimentally derived data of a model ship with an antiroll tank, a numerical simulation was established. The numerical model was then compared with the free-running model experiments. The results indicated that the numerical model could qualitatively verify the experimental results. Finally, an attempt to optimise the size of an antirolling tank for preventing parametric rolling for the subject post-Panamax container ship in the North Pacific Ocean is presented.