| Due to the impact of the wave and wind, ship will inevitably have sway movement when it sails in the ocean. At this time, some mistakes cannot be avoided and could cause accidents if only rely on the experience when the crew steers.If we can predict ship motion through the theoretical methods to guide the sterner, the rate of the accidents would be reduced to some extent. Due to that, this paper contains calculation of the frequency response functions of the trawler in regular waves under different routing states. Based on the linear theory of stationary random process and description of the wave spectrum, I calculate three seakeeping factors (heave, pitch, and roll) in random waves which is more important for the ship security. And analyze the relationship between the different vessel elements (draft, displacement, etc) and the ship motion performance. This will intuitively reflect the relationship between the wave response and the status of the ship. The occurrences of propeller emergence and green water have been discussed. The natural rolling period always varies as the load condition may change. And it matters when it comes to steering. This paper has given out the cooperation condition of ship speed and wave encounter angle when resonant rolling happens. With the guidance, the driver can effectively ensure the safety of the ship.Fast ship in calm water may not be a fast ship in waves. Added resistance is a important content of seakeeping performances. Added resistance is not conducive to the task completion of ships, it will low down the economic benefits. So it is important to predict the added resistance and speed loss. The paper has expounded the nature of added resistance, and introduced the ITTC recommended speed-loss-solving methods (experimentally and theoretically). Calm water resistance, added resistance, wind resistance, characters of the propeller and the main engine are all needed to know before solving the speed loss. Calm water resistances are solved by commercial software and compared with experiment data for validation. Energy saving and emission reduction are also concerned. Adjust floating state to obtain calm water resistance values under different floating states, and the best pitch angle of the ship sailing has been shown. Use empirical formula to get wind resistance. Based on strip method for prediction of added resistance in waves, the author calculates the added resistance in different load states and sea conditions. Combined with the ITTC recommended RTIM with characteristic curves of screw propeller, the power of the main engine in waves can be acquired, and then we can get the speed loss. |
