Dynamic Behavior of a Fishing Boat Moored in Harbor

Abstract

It is important to predict the dynamic behavior of a fishing boat moored in harbor. Because, the extraordinary mooring line forces and ship motions cause damage e. g. break of mooring lines or collision with a quay. These dynamic behavior differs from that of a large ship in harbor or a moored offshore structure. That is, a fishing boat is usually moored perpendicular to a straight quay in longitudinal waves. Further, her mooring lines have completely non-linear characteristics.Then the authors carried out the numerical simulation in time domain ; in which wave forces and mooring forces were evaluated by theories and viscous damping coefficients were derived from free decay tests. We got the stochastic values of surging motion and mooring line forces in irregular waves.Moreover, we conducted model experiments in a tank. A model ship was moored in front of a model quay. Its motions and mooring line forces in irregular waves were measured by means of an optical tracking system and ring-type strain-gauge transducers, respectively.As a result, the values computed by our numerical simulation procedure were in good agreement with the experimental values. Then it is shown that our proposed simulation procedure is effective to predict the safety of a fishing boat moored in harbor. In particular, we found that wave exciting surge force can be estimated by Froude-Krylov hypothesis and mooring forces can be estimated by the static mooring characteristics and the surging motion of a ship. Furthermore, we discussed the effect of waves, mooring systems and quay structures on the dynamic behavior of a fishing boat.