The Effect of Water Filling Level in a Live-Bait Tank on the Stability of a 20 GT Pole and Line Fishing Vessel

Abstract

The stability of pole-and-line fishing vessels equipped with a live-bait tank is heavily influenced by the free surface effect caused by the water load. The sloshing motion of the load inside the tanks can increase the dynamic pressure on the tank walls and generate heeling moments (Mh) that may reduce the vessel’s stability. This study aims to analyze the effects of water filling level ( ) variation, roll excitation frequency, and roll angle (θ) on the distribution of hydrostatic and dynamic pressures, and their implications for vessel stability. Numerical simulations were conducted using Computational Fluid Dynamics (CFD) in the Ansys Fluent with the Volume of Fluid (VOF) method in a hull-shaped tank under transient conditions. A dynamic mesh was applied to track the fluid-free surface, and a pressure-based solver employing the k-ω Shear Stress Transport (SST) turbulence model was used and verified through a grid-independence test. The simulations were performed for H between 10% and 90% of the tank height, roll excitation frequencies between 0.5 and 2.5 rad/s, and θ between 5 ° and 20 °. The results showed that the highest dynamic pressure values were recorded near the free surface under all filling conditions. Roll frequency and θ significantly affected the pressure when the H in the tank was approximately 50% of the tank height. At an H of 90%, the pressure on the tank walls did not show any significant variation. Compared to the low filling condition (10%), the average sloshing pressure increased by more than one order of magnitude as approached 70% of the tank height. The Mh induced by water pressure on the tank walls increased with higher H and with the ratio of free surface height to width. The representative sloshing-induced Mh increased by approximately 85% at a 90% filling level compared to the 10% filling condition. The lowest gradient of Mh increase occurred at water levels between 50% and 70%, corresponding to a free-surface height-to-width ratio of 0.21–0.27. The influence of resonant frequency on the disturbing arm (GZh) was more pronounced when the was below 50% of the tank height than at higher H. The maximum GZh of 0.013 m occurred at an H of 90%, with a roll frequency of 2.5 rad/s and a θ of 20 ° corresponding to the reduction of righting arm (GZr) of 1.82% of the original. These results indicated that the vessel maintained sufficient stability to counteract the Mh generated by the water motion within the live-bait tank.

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