A lubber line is a fixed line on a compass binnacle or radar plan position indicator display pointing towards the front of the ship or aircraft and corresponding to the craft's centerline (being the customary direction of movement).
The line represents 0 degrees and is therefore the zero-point from which relative bearings are measured, e.g., "twenty-degrees to port".
Compasses on sailboats may have additional lubber lines at forty-five degrees from the centerline. This represents about as close to the wind as the average boat will sail. These lubber lines may be used when sailing close hauled to see if you are on the closest course to your destination, without having to add or subtract the 45 degrees every few minutes, or recalculate your required heading every time you tack. The main line on the compass reads your current (close-hauled) heading and the leeward lubber line will read the bearing to your destination, regardless of whether you are on port or starboard tack. Lubber lines also help you to see windshifts when racing. If you are sailing close-hauled with good trim and you notice that your bearing to the windward mark starts to drift outside the lubber line (angle becoming greater than 45 degrees) you are being headed, and should consider tacking.
Famous quotes containing the words lubber and/or line:
“Up through the lubber crust of Wales
I rocketed to astonish
The flashing needle rock of squatters,
The criers of Shabby and Shorten,
The famous stitch droppers.”
—Dylan Thomas (1914–1953)
“The real dividing line between early childhood and middle childhood is not between the fifth year and the sixth year—it is more nearly when children are about seven or eight, moving on toward nine. Building the barrier at six has no psychological basis. It has come about only from the historic-economic-political fact that the age of six is when we provide schools for all.”
—James L. Hymes, Jr. (20th century)