As a ship moves forward through the water there is a tendency to form a cavity or hollow at the stern. Water swirls round the sides to fill the cavity. This follow up is called the wake current. The current is strongest at the surface and decreases as the depth increases towards the keel. The wake current is more pronounced in vessels of full form than in those of fine lines. Flat-bottomed, square-sterned barges are difficult to steer as the strong wake current tends to neutralize the effect of the flow of water aft towards the rudder due to the vessels headway. The wake current reduces the steering power of the rudder when going ahead.
