12.38 Magnetic Instruments

12.38.2 Given a sample deviation card, show how to apply corrections.

12.38.4 Briefly:

(a) describe the construction of a present-day direct-reading compass;

A present-day direct-reading compass consists of a magnetic needle suspended on a pivot, which is mounted in a circular housing that is graduated in degrees. The housing is filled with a liquid, usually oil, that dampens the movement of the needle and reduces errors due to vibration. The compass is mounted on a gimbal ring that allows it to remain level and compensate for the pitch and roll of the vessel. The compass is also equipped with a deviation card that provides corrections for errors due to magnetic influences on the vessel. The compass is typically illuminated for use at night or in low light conditions.

(b) define lubber line;

A lubber line is a fixed line or mark on a compass that indicates the direction the compass is pointing relative to the centerline of the vessel. The lubber line is used as a reference when taking compass bearings and is typically aligned with the vessel's keel or centerline.

(c) the functions of the fluid in the compass bowl.

The fluid in a compass bowl serves several functions, including: