Equipment Guide · Gyrocompass
The gyrocompass finds true north with no magnetism at all — just a rotor spinning at thousands of rpm, the pull of gravity, and the fact that the earth turns underneath it. Tap a step or press "Play" to follow the physics from rigidity in space to the settled meridian, see why the compass asks you for speed and latitude, and how one master feeds the radar, ECDIS and autopilot — then take the simulator to 60° north at full speed and see the error you would have to apply by hand.
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The compass balances on the earth's rotation, and it takes the resultant of the earth's eastward sweep plus your own motion as its east. At 60°N the surface moves east at 450 knots; add 20 knots of ship heading north and the resultant tilts by 20 ÷ (15.7 × 0.5) ≈ 2.5° — so the settle point sits 2.5° west of true north, and the gyro reads 2.5° high on every course and every bearing. Steer 000° by that repeater and you actually make good 357.5°: after a 60-mile run you are about 2.6 miles west of your track — in coastal water, a grounding-sized error from a compass working exactly as designed. Modern compasses subtract it automatically, if the speed and latitude they are fed are right.
Set latitude, speed and course, and watch where the gyro settles against true north. Switch the corrector OFF to see the raw speed error every navigator once applied by hand — then push the latitude past 80° and watch the compass lose its grip on north altogether.
Sim thresholds — apply the error from 0.5° · false course from 2.0° unapplied · polar wander from 80° latitude. 1-in-60 rule: each 1° ≈ 1 nm off per 60 nm run.
The rose shows where the gyro's axis settles against true north (offset drawn ×10). With the ship's head on the ordered course, every repeater shows ordered + error — and steering by the repeater walks the ship off the ordered track by the same angle. The directive force bar is the north-seeking torque, which fades with cos lat: at the equator the compass is stiffest, at 80°+ it barely knows where north is.
Press Start to run the compass — switch the corrector OFF to see the raw speed error, then push the latitude past 80°.
Working principle — explained in our own plain words with our own schematic from general marine knowledge (not copied from any OEM manual). Conceptual; varies by ship/model. Reviewed and verified by a Master Mariner.