Which term would you use to describe a position directly on the central line of a ship?

The term that describes a position directly on the central line of a ship is "centerline." This term refers to an imaginary line that runs from the bow (front) to the stern (rear) of the ship, effectively bisecting it into two equal halves. It serves as a crucial reference point for navigation and structural considerations on a vessel.

The other terms, such as starboard and port, denote specific sides of the ship; starboard refers to the right side when facing the bow, while port refers to the left side. The term "aft" relates to the back section of the ship, again not indicating a position on the central line. Understanding these terminologies helps in accurately conveying information about a ship's layout and navigation.