A proposed criterion for assessment the pure loss of stability of ships in longitudinal waves

One of the most important nautical qualities of the ship is intact stability. During encountering heavy weather conditions, vessels are exposed to large variations of stability in waves, leading to loss of intact stability or even capsize. One of the phenomena that lead to ship's dynamic instabilities is pure loss of stability in longitudinal waves. The present paper describes a proposed criterion for the assessment of ship's vulnerability to such phenomenon, before starting the voyage, based on the hydrostatic characteristics of the ship and actual loading condition. The proposed method for intact stability loss evaluation in longitudinal waves, when parametric roll might occur, is based on the criterion of the ship's time spent on wave crest condition. This method can be used as a guidance or computational tool for the officers on board vessel.