The essentials in 30 seconds
- 3 technologies coexist: magnetic fluxgate (entry-level, 80% of recreational fleet), fiber-optic gyro (pure racing, IMOCA), 9-axis attitude sensor (modernity 2020+, current standard).
- Navico Precision 9 = 2026 standard. Magnetometer + MEMS gyro + 3-axis accelerometer combo for ~ $533 ex-VAT. Heading accuracy ±2° static, ±5° in rough seas. Natively compatible with B&G/Simrad/Lowrance.
- Raymarine Evolution: Raymarine T909 fluxgate compass (~ $183 ex-VAT) compatible with Axiom + EV-100/200/400.
- Offshore racing: Madintec MAD Sensor Motion (racing attitude sensor ~ $850 ex-VAT) or KVH fiber gyro (premium, $3,000–$5,000).
- Workshop verdict: Precision 9 for 80% of sailboat refits 30–50 ft. Raymarine T909 if pure Raymarine ecosystem. Madintec only for serious IRC racing.
The electronic compass is the sailboat’s directional sense. It feeds the autopilot with heading, the displays with heading, and the radar with course. Without a good compass, there’s no good autopilot — it’s the first thing checked when an autopilot oscillates. This article distinguishes the 3 available technologies and the brands distributed by Skysat.
For autopilots using the compass, see B&G vs Raymarine autopilot.
The role of the compass in the autopilot system
The compass continuously sends (10–20 Hz) three critical pieces of data:
- Magnetic heading: the direction the bow points. Feeds the autopilot in "Compass" mode and the radar for orientation.
- Heel (roll): the angle of lateral tilt. Useful for autopilot compensation in rough seas.
- Pitch: the angle of longitudinal tilt. Compensates autopilot corrections in swell-induced pitching.
Magnetic fluxgate — technical details
Electromagnetic sensor measuring Earth’s magnetic field. Historic technology since the 1970s.
- Accuracy: ±2° in calm water, drift to ±5–8° in rough seas (ferromagnetic effects + acceleration).
- Frequency: 5–10 Hz.
- Limitation: sensitive to nearby metal masses (engine, stainless rigging, batteries). Install at least 1 m away from these masses.
- Brands: Raymarine T909 (~ $183 ex-VAT), Garmin GHC50, B&G H5000 RC42.
Fiber-optic gyro — technical details
Fiber-optic gyro measures rotation via the Sagnac effect. Technology inherited from military inertial navigation.
- Accuracy: ±0.1° immune to magnetic interference.
- Frequency: 50–100 Hz.
- Limitation: slow drift (1–3°/h) without external reference (GPS heading).
- Brands: KVH (USA), Furuno (Japan).
- Price: $3,000–$15,000 ex-VAT. For racing/commercial only.
9-axis attitude sensor — the modern solution
3-axis magnetometer + 3-axis MEMS gyro + 3-axis accelerometer in a single unit. Software fusion for heading + attitude + acceleration.
- Accuracy: ±2° static, ±3–5° in rough seas (acceleration compensation).
- Frequency: 10–50 Hz depending on model.
- Advantage: compensates magnetic interference via gyro + accelerometer fusion. More stable in rough seas than fluxgate alone.
- Brands: Navico Precision 9 (~ $533 ex-VAT) = 2026 recreational standard. Madintec MAD Sensor Motion (~ $850 ex-VAT) = French racing standard.
Technical comparison table
| Model | Technology | Accuracy | Frequency | Price ex-VAT |
|---|---|---|---|---|
| Raymarine T909 | Fluxgate | ±2° static, ±8° rough | 10 Hz | ~ $183 |
| Navico Precision 9 | 9-axis sensor | ±2° static, ±5° rough | 10 Hz | ~ $533 |
| B&G H5000 RC42 | Fluxgate | ±2° static, ±8° rough | 10 Hz | ~ $850 |
| Madintec MAD Sensor Motion | 9-axis racing sensor | ±1° static, ±3° rough | 50 Hz | ~ $850 |
| KVH fiber gyro | Fiber gyro | ±0.1° | 100 Hz | ~ $5,000 |
Workshop verdict by program
Coastal cruising 30–40 ft — basic fluxgate
If existing Raymarine Evolution autopilot: T909 (~ $183 ex-VAT) is sufficient. For a full refit: Precision 9 from the start for long-term stability.
Offshore cruising 40–50 ft — Precision 9
Skysat workshop standard. ~ $533 ex-VAT, native integration with B&G + Lowrance + Simrad + Raymarine via N2K. Stable in rough seas.
Offshore racing IRC / RORC — Precision 9 or Madintec
Precision 9 sufficient for club-level IRC. Madintec MAD Sensor Motion for serious IRC and offshore with fine polar data.
IMOCA / America’s Cup — KVH fiber gyro
Pure high-level racing. Investment $5,000+ ex-VAT but unmatched accuracy.
Installation and calibration
Workshop rules — compass installation
- Position: center of the boat, mid-height, at least 1 m away from any metal mass (engine, batteries, rigging).
- Orientation: respect the front marking (sensor arrow pointing to bow).
- Calibration: mandatory post-installation. Make 2–3 full boat circles in calm water, at 2–3 knots, no current. The compass learns the boat’s magnetic signature.
- Declination adjustment: set local declination (Brest area = -1°, Caribbean = -15°) via software.
- Re-calibration: every 2–3 years or after significant onboard changes (added batteries, metal antenna, metal solar panels).
FAQ — Electronic compass
Is a cockpit magnetic compass sufficient?
No, it’s complementary. A cockpit magnetic compass is mandatory (Division 240) for visual safety. The electronic compass feeds the autopilot and chartplotter. Both are required.
Does GPS heading replace the compass?
No. GPS provides COG (Course Over Ground = ground track), not HDG (heading). Critical difference in the presence of current. The compass is mandatory in addition to GPS.
Why does my compass drift in rough seas?
Fluxgate alone = sensitivity to accelerations + moving metal masses. Compensate with a 9-axis sensor (Precision 9) that filters accelerations via integrated gyro and accelerometer.
How often to calibrate?
Initial calibration mandatory. Recalibrate every 2–3 years or after significant onboard changes. The boat’s magnetic signature slowly evolves with re-caulking (corrosion), paint (metallic paint), or added ferrous equipment.
Is an attitude sensor useful for the autopilot?
Yes. It’s the #1 difference between fluxgate and 9-axis. The autopilot receives heading + heel + pitch, allowing intelligent compensation of oscillations in rough seas. Documented reduction of unnecessary corrections by 30–50%.
Skysat distributes B&G/Navico, Raymarine, Garmin and Madintec. 2026 ex-VAT prices are indicative of authorized distributor rates.
