Large Amplitude Rolling and Strongly Nonlinear Behaviour of Multihull Ships in Moderate Beam Waves

A trimaran and a pentamaran ship have been investigated to study the effect of transversal hull separation on roll motion in waves using typical outriggers with small beam and draft. The experiments in regular waves revealed the extreme sensitivity of these hull typologies to roll motion in beam waves, even in mild sea conditions. Two configurations of the trimaran and one of the pentamaran exhibited a multivalued roll response curve in the low frequency range. This is, to the best authors’ knowledge, the first published experimental evidence of bifurcations in roll motion of multihull ships, which are usually designed and selected for their superior stability characteristics and low rolling amplitude. Simulations have been performed by means of a linear seakeeping approach extended to take into account nonlinearirites for damping and restoring, and by using a nonlinear 1-DOF model for roll.