Parametric Analysis of the Stability of a Family of Fishing Vessels

In this paper, the safety problem of fishing vessels is considered in connection with the possibility of their loss in waves. To this end, different dynamic mechanisms are studied in detail, ranging from capsizing to loss of control and/or broaching-to phenomena. Firstly, the stability is investigated in the light of the existing I.M.O. criteria and the new method of energy-balance proposed by Strathclyde University is illustrated. Finally, the set of differential equations describing the dynamics of the antisymmetric motions of roll, yaw and sway is obtained with hydrodynamic derivatives estimated from manoeuvrability and geometric parameters. The calculations are made on a family of 40-50 meters long fishing vessels of the BSRA trawler series. It results that, in general, I.M.O. statistical criterion is less restrictive than I.M.O. weather criterion and both fall into a region of approximately 20-30 percent of net area positive according to energy-balance method. An analysis of stability the antisymmetric motions reveals the possibility of dangerous phenomena depending on the trim condition and on the Froude number. For the same family, an analysis of the threshold for the onset of parametric rolling in a following sea reveals the extreme sensitivity of this type of vessels to such a particular capsizing mechanism.