Applet shows a boat crossing a river. The idealized river has same velocity form bank to bank. The velocity of the boat relative to river ( VBR Blue arrow ) points in the direction of the bow and the boat would have traveled in that direction in still water. ( You could check this by setting the velocity of the river to zero. ) The river causes the boat to drift in its own direction. The river velocity VRG is shown in red. The velocity of the boat relative to ground ( VBG Black arrow ) is the direction of motion of the boat as seen by ground observer. This vector is sum of the velocity of boat relative to river and velocity of river relative to ground. ( VBG = VBR+ VRG ) You can change the magnitude of the velocity of the river and the magnitude and direction of the velocity of the boat using the appropriate scroll bars.