The correct prediction of a vessel’s reaction to a specific command demands the complete comprehension of both the nature and the forces that are applied on it.
There are six sources of forces that can influence a vessel. These are the propeller, the rudder, the static line, the anchorage means, the wind, and finally, the current.
The first four sources are controlled by the vessel. As far as the wind and the current are concerned, although they are not controlled, if properly exploited, they can support the mariner’s efforts. We have to always keep in mind that although these forces exist, the movement takes place only after the inertia has affected the vessel.