Nautical Term: Beam line
Definition of Beam line
A beam line is an imaginary line that runs perpendicular to the ship’s beam (the side of the ship that is perpendicular to the direction the ship is heading). The beam line can be visualized as the line where the water would touch the top of the frame line, which is the topmost part of the ship’s hull that is in contact with the water. For example, when a ship is maneuvering in the water and the captain wants to know the ship’s heading relative to a specific point on the horizon, the ship’s navigators can use the ship’s heading and the angle of the beam line, which can be determined from the ship’s speed and direction, and the water’s depth and current, to calculate the ship’s true heading and its position on the water relative to the specific point on the horizon.
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