A graduated circle printed on nautical charts showing both true and magnetic north, used to determine bearings and courses. The outer ring indicates true directions while the inner ring shows magnetic directions adjusted for local variation.
Category: Navigation & Seamanship
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BeamThe width of a vessel at its widest point, measured at the midship section.BowThe forward-most part of a vessel's hull, designed to reduce the resistance of the hull cutting through water.Chart DatumThe reference level from which depths on a nautical chart are measured, typically the lowest astronomical tide (LAT).CourseThe intended horizontal direction of travel measured as an angle from north.Course Over GroundThe actual direction of a vessel's movement over the earth's surface, as determined by GPS or other positioning systems.Dead ReckoningA method of estimating a vessel's current position by advancing a known position using the course steered, speed through the water, and time elapsed.
Back to DictionaryEntry updated May 2026