What are Lubber Lines?

Lubber Lines

For ages, the magnetic compass has been considered the most essential device or instrument for navigation in the vast stretches of the seas.

In today’s time, advanced mechanisms like GPS or digitised systems using high-end satellite data help in navigation and keep the vessel communicable from literally everywhere. The compass is still present in almost all vessels as a standby and still upholds its importance.

Now, reiterating the simple aspects, the magnet or associated devices as the magnetometer works on the basic principle of geomagnetism, showing the directions based on the earth’s inherent magnetic field.

Thus, when the compass needle points somewhat towards the north, your vessel is headed towards the northern direction.

Now, while analysing compasses, some form of reference is crucial in determining the direction with respect to the vessel’s heading. For this reason, the use of lubber lines comes into the picture.

Lubber lines are calibrated marks inside the dial or the binnacle of a compass that shows the direction of the vessel’s centreline, that is, the foe-aft orientation of the vessel. They appear as a thin line or a mark or a strip aligned with the vessel’s direction of heading.

Lubber Lines 1

Now, for all practical purposes, as the compass or any other form of navigation instrument is located towards the front side of the vessel on the bridge, the lubber line is mostly straight when viewed on the device.

Lubber lines essentially act as a reference for navigation and give the resultant angle of the vessel’s course of heading and any given direction.

For example, in a compass, when the lubber line makes an angle of about 45 degrees concerning the North direction, the vessel is headed in a direction about 45 degrees offset from the north. The lubber line also alludes to the line of 0 degrees with the vessel’s heading.

There may also be other additional lubber lines at intervals of 45 degrees from the main one in many cases. In modern devices like GPS or radar navigation charts, the lubber line is often displayed digitally on the console or screen.

The term is derived from the nautical term lubber meaning a sailor.

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About Author

Subhodeep is a Graduate of Naval Architecture and Ocean Engineering. He has deep interest in marine structures and goal-based design aspects, and is dedicated to sharing and propagating technical knowledge of the industry.

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