This paper describes a means by which the capsize risk associated with various fishing vessel operating conditions can be evaluated. Rather than relying on the static restoring moment curve as the primary criteria for vessel safety, modern nonlinear systems analysis is applied to the problem of extreme nonlinear rolling in random beam sea. While the method is quite general and not limited to small vessels, it is illustrated with a specific application involving Native American trap net fishing on the upper Great Lakes. General trap net operations, as practiced by Native American fishermen and women in the Grand Traverse Bay region, are presented in detail. The most significant characteristic of trap net operations is the heel induced during net deployment and net lifting. The increased risk to the vessel, in terms of the increased probability of capsize is quantified for various heel angles and various sea states. A significant advantage of the capsize analysis method presented here is its ability to investigate quickly the effects of many parameters (e.g., trap net line tension, wave height, and/or wave period) on a nonlinear dynamic system without having to resort to extensive simulation studies.
Nonlinear Rolling Motion of Ship in Random Beam Seas
