The seakeeping qualities of fishing vessels in Japan are generally poorer in small boats than in larger vessels. Ship motion frequently exhibits strong nonlinear responses to external forces due to the typical ship forms. This has resulted in many serious marine accidents and fatalities. To improve the safety of small fishing boats with structural vulnerabilities, it is necessary not only to understand their basic stability, but also to estimate accurately the structure of the dynamic response characteristics for external forces. In addition, the regulation of gross tonnage (GT) in the Fishing Vessel Act resulted in the restriction of various improvements of fishing vessels. Many scientists studying fishing vessels pointed out this problem, and in 2018, the law was finally revised, so the structure and safety are expected to improve in near future.
In this paper, I show some typical methodologies for studying the dynamic response structure to improve the safety of fishing vessels currently in use and of future fishing boats.