A lubber's line is a fixed, vertical reference line on the inside of a compass bowl or radar display that aligns with the longitudinal centerline (bow) of a ship or vessel. It serves as a visual pointer, indicating the current heading of the vessel relative to the rotating compass card.

Key Aspects of the Lubber's Line:
Purpose: It helps the helmsman maintain a steady course by showing which compass heading is directly ahead of the bow.

Location: Commonly found as a painted line or small needle on the binnacle (compass housing).

Usage: If the ship is heading North (N), the N on the compass card will align with the lubber's line.

Origin: The term is derived from "lubber" (meaning an inexperienced seaman), as it provides an easy-to-read reference for keeping the ship on course.