The general formula of navigation problem (1): still water speed (ship speed)+current speed (water speed) = downstream speed; Ship speed-water speed = water flow speed; (downstream speed+upstream speed) ÷2= ship speed; (downstream speed-upstream speed) ÷2= water flow speed. (2) The formula for two ships sailing in opposite directions: downstream speed of ship A+upstream speed of ship B = still water speed of ship A+still water speed of ship B; (3) The formula for two ships sailing in the same direction: the still water speed of the rear (front) ship-the still water speed of the front (rear) ship = the speed at which the two ships narrow (expand) the distance.