The authors have discussed the new conceptual neurophysiological model of genesis and pathogenesis of fatigue and overstrain in seamen. The complex phase character of the developing changes was revealed. Use of the complex of psychophysiological methods with consideration of neurophysiological nature of the changes detected allowed us to obtain the objective assessment concerning fatigue and overstrain in seamen. It is shown that the existing conceptions about the dynamics of nervous processes developed in seamen during fatigue and overstrain including those described in the corresponding documents of the Navy and their evaluation are too simplified and theoretically incorrect. These incorrect concepts practically prevent the conduction of appropriate medical and prophylactic measures, complicate the standardization of some characteristics of habitability of the Navy ships and submarines, not ensure trouble-free conditions at sea in terms of human factor.