What are the resistances encountered by ships during navigation?

There are air resistance and water resistance during sailing.

When a ship is sailing, the resistance of fluid to navigation is the component of the resultant force of fluid (water and air) projected on the hull in the direction opposite to the sailing direction. According to different classification methods, it can be divided into friction resistance, pressure resistance, appendage resistance, air resistance, wave breaking resistance, viscous resistance, viscous pressure resistance, residual resistance, wave resistance and other components.

Ship resistance includes water resistance and air resistance. Because the density of water is more than 800 times higher than that of air, the ship's hull water resistance is mainly considered when sailing at sea.

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When a ship sails on the water, the hull moves in two fluid media, air and water, and it will inevitably be resisted by air and water. For the convenience of research, the total hull resistance can be divided into air resistance and water resistance according to fluid types.

Air resistance refers to the reaction of air to the water part of the hull. Water resistance is the reaction force of water to the underwater part of the hull.

Further, the water resistance is divided into two parts: still water resistance and additional resistance (also called small wave resistance) within the wave limit when the ship is sailing in still water. Hydrostatic resistance is usually divided into bare hull resistance and appendage resistance.

The so-called appendage resistance refers to the resistance value increased by appendages such as rudder, stern keel and axle frame protruding from the exposed hull. According to this control method, the resistance encountered by ships sailing in water is usually divided into two parts: one part is the bare hull resistance suffered by the bare hull in still water, and the other part is the additional resistance, including air resistance, rough resistance and additional lift.