lubber's line

American  

Or lubber line

noun

Navigation.

1. a vertical line on the forward inner side of the bowl of a fixed compass, used as a reference mark indicating the heading of a vessel.

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Etymology

Origin of lubber's line

First recorded in 1855–65

Example Sentences

The lubber's line was a point west of north.

From Project Gutenberg

If the glass dial be revolved until the degree of demarcation, which is coincident with the right ahead marking on the flat ring, is the same as that which points to the lubber's line of the ship's compass, then all directions indicated by the glass dial will be parallel to the corresponding directions of the ship's compass, and all bearings taken will be compass bearings, i.e., as though taken from the compass itself.

From Project Gutenberg

You observe that the thoughtful Polton has stuck a piece of thread on the glass of the compass to serve as a lubber's line.

From Project Gutenberg