ABSTRACT

The roll motion in regular beam waves of two catamarans, one with rounded lines and the second with knuckles was studied both starting from upright equilibrium position and in the presence of a list due to asymmetric loading or asymmetric flooding. The simulations obtained with two mathematical models, one based on a monohull "roll" approach and the second based on a twin hull "heave" approach were compared with experimental results relative to several values of hull separation. The results highlight the mechanics of roll motion of multihull ships and the effect of asymmetric flooding.

INTRODUCTION

The existing stability rules both in intact ship and after damage are presently based on static and dynamic levers of stability calculated in calm water. On the other hand, the weather criterion is based on a quite rough description of the action of the marine environment on the ship. In particular, the formulas used to evaluate the roll amplitude are considered unsatisfactory. In this paper, the problem of ship safety has been studied with regard to the stability and rolling motion of catamaran ships in beam waves. The research was aimed to obtain detailed information on ship behavior in both intact and damage conditions. To this end, two catamaran ship scale models were built and tested in the hydrodynamic laboratories of DINMA - University of Trieste, one with round lines and the other with hard chines. Several configurations corresponding to different values of the hull separation were tested. Transversal upright equilibrium position together with loading conditions with a list were realized, these latter being obtained by means of unsymmetrical additional loading or flooding one of the hulls. The two different loading cases were calibrated to match the same static heeling in calm water.

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