The magnetic compass remains the most reliable navigation instrument aboard any vessel — no battery, no software, no signal required. These guides cover how it works, how to identify and correct its errors, and how to use it for position fixing and coastal navigation. They are written for sailors who want to navigate confidently without depending on electronics.
The Magnetic Compass: How It Works
Variation, deviation, the True Virgins mnemonic, reading the compass rose on a paper chart, and why every serious sailor must be able to navigate on the compass alone.
- True vs. magnetic north
- The TVMDC formula
- Fluxgate vs. liquid-dampened
Compass Deviation: Your Boat's Own Magnetic Field
What causes deviation, why it changes on every heading, how to read a deviation card, what destroys compass accuracy underway, and how corrector magnets work.
- ±15° on metal boats
- The deviation card explained
- What kills accuracy at sea
Swinging the Compass
How to measure deviation on all headings using a shore range or buoy turn, how to record a deviation table, fitting corrector magnets, and when to hire a compass adjuster.
- Shore range method
- Heeling error correction
- Adjuster fee $150–$300
The Hand-Bearing Compass
Taking bearings on charted objects, plotting the three-bearing fix and the cocked hat, setting a danger bearing, and cross-checking your chartplotter against a visual bearing.
- Three-bearing fix
- Danger bearing technique
- Plastimo vs. Davis
About These Guides
These are editorial resources for recreational and professional mariners. Magnetic variation changes over time; always use current charts and the most recent Notice to Mariners for your area. Compass deviation is specific to each vessel — figures given here are illustrative. For offshore work, consult a qualified compass adjuster and verify your deviation card against a known range before departure. See the full cruising guide library for additional navigation resources.