There are many factors that affect the ship's resistance, among which the speed, ship type and external conditions are the main ones. For a large number of medium and low speed ships, the viscous resistance is much greater than the wave-making resistance; For high-speed ships, it is mainly to reduce the wave-making resistance. The main measures to reduce the resistance are: (1) optimizing the main dimension and line shape of the ship. At present, there are many ship types and lines in use: ① spherical nose bow (variable spherical nose bow has been developed abroad, and its nose can move up and down, or swing freely, or change the shape of the sphere according to the change of draft and speed); ② Stern ball type; (3) spherical stern and double stern ship type; ④ Longitudinal ship type; ⑤ Catamarans and small waterplane catamarans; ⑥ Asymmetric stern line type; ⑦ shallow draft fat ship type; ⑧ Twin-stern ship and flat-headed vortex. In many cases, it is necessary to study to what extent the fuel consumption rate can be reduced and whether it is necessary to re-determine the propeller design point. The influence of changing the design point by increasing the rotational speed on the propeller can not be ignored, otherwise the improvement obtained by changing the design point and the influence on the propeller itself may cancel each other out. (2) Reduce the roughness of the hull. After a ship is used for a period of time, the roughness of the hull will increase due to corrosion. At the same time, the fouling and attachment of marine life to the hull is becoming more and more serious. These are enemies of conservation of energy. According to rough statistics, due to the increase of roughness, about 30% more sleeves are consumed every year. The countermeasures to prevent fouling are: adopting advanced antifouling coating system to prevent marine organisms from adhering, such as using self-polishing hull paint; (2) electrolyze seawater to prevent pollution, and decompose seawater into chlorine gas through an electrolysis device to kill marine life; ③ Regular docking and bottom cleaning; ④ Underwater cleaning (scraping the bottom of the ship); ⑤ Wiping touch-up coating technology. The countermeasures to prevent galling are as follows: ① Correct selection of reasonable coating system; (2) improve the coating construction quality; (3) Cathodic protection of the underwater part of the hull; ④ Polishing the hull plate. (3) Adopt stern attachments (such as fins and draft tubes). ) Using the stern appendage can not only improve the flow field at the stern, thus reducing the viscous pressure resistance, but also improve the propulsion efficiency of the propeller. At present, the appendages used are: ① reaction fin; ② Anterior catheter; ③ Additional thrust fins; ④ Stern ball and rudder with fins; ⑤ Fix the impeller behind the blade.