Research On The Stability Analysis Method Of Fishing Vessels In Harbor

In recent years,under the influence of global warming,the surface temperature of the tropical ocean has risen,which has significantly increased the frequency and average power of typhoons and hurricanes.When a typhoon comes,fishing boats usually enter the fishing port ahead of time for shelter.With the frequent occurrence of typhoons and the increase in intensity,the stability and the ability to resist wind and waves of fishing boats moored in the fishing port under extreme weather become more and more important.Although relevant regulations provide calculation methods for ship stability,most of the existing regulations are applicable to natural sea conditions,and there are blind spots in the regulations for the stability calculation of ships in fishing ports.Shengsi Central Fishing Port currently has an old port area and a new port area.The old port area has serious sedimentation,fishing boats need to enter the port at high tide,and the fishing boats in the port are stranded at medium and low tides.Before the completion of the new port area,due to the limited capacity of the port area,when encountering severe typhoon weather,fishing boats near the Shengsi waters could only go to Ningbo,Shanghai,Zhoushan and other fishing ports for shelter,and the cost of round-trip navigation was high.After the completion of the new port area,it can accommodate more fishing boats for shelter from the typhoon.Based on design requirements,it is necessary to analyze the stability of the ships moored in the port area under the typhoon condition and the motion response analysis of the mooring state to determine the anti-wind and wave level of the new port area.There are three main ways of berthing fishing boats in Shengsi Fishing Port:(1)stranded mooring;(2)mooring side by side in front of the wharf;(3)mooring at a deep-water anchorage in the port area.The wind and waves at the wharf are very small,which can ensure the fishing boat’s need to avoid typhoons.This paper mainly analyzes the stability of large inclination angles for two situations:stranded mooring and mooring in the port area.The current stability check method is aimed at floating ships or offshore platforms in offshore and far-sea navigation areas,and cannot meet the needs of large-angle stability analysis when the ship is stranded.At the same time,the wave conditions in the port area(H_s=0.5m)are much smaller than the open sea(H_s=3.5m).Using the existing regulations to check the stability of fishing boats in the harbor is too conservative and cannot reflect the protective effect of the breakwater on the fishing boats in the harbor.Aiming at the characteristics of the fishing boats in the harbor when they are stranded and moored,this paper proposes a method for calculating the large inclination restoring moment of the fishing boats in the stranded state,which solves the technical difficulties of the stability analysis of the stranded state;In view of the wave conditions of the fishing boats in the harbor,a hydrodynamic method is proposed to calculate the maximum heel angle of the fishing boat in the moored state,and the heel angle is used as the initial heel angle for the stability analysis of the large inclination angle to calculate the ultimate wind inclination moment of the fishing boat.This method improves the accuracy of stability analysis.The stability analysis results under the two conditions show that the fishing boats in the Shengsi Fishing Port can maintain sufficient stability when the wind speed is below 95.12m/s(equivalent to a typhoon of category 17).