A more thorough explanation:

Definition: A missing ship is a vessel that has been gone for an unreasonably long time, leading to the presumption that it is lost at sea. This includes a vessel that has been gone longer than the average time it takes a vessel to make a similar voyage in the same season.

Example: A cargo ship that was expected to arrive at its destination port two weeks ago has not been heard from since it left its last port. Despite search efforts, there has been no sign of the ship or its crew. This ship is considered a missing ship.

Explanation: The example illustrates a missing ship as it has been gone for an unreasonably long time and has not been heard from despite search efforts. The presumption is that the ship is lost at sea, as it has been gone longer than the average time it takes a vessel to make a similar voyage in the same season.