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)
“It is a great many years since at the outset of my career I had to think seriously what life had to offer that was worth having. I came to the conclusion that the chief good for me was freedom to learn, think, and say what I pleased, when I pleased. I have acted on that conviction... and though strongly, and perhaps wisely, warned that I should probably come to grief, I am entirely satisfied with the results of the line of action I have adopted.”
—Thomas Henry Huxley (1825–95)