Module 9 - Compass
Deviation
Deviation is the error caused by magnetic influences on YOUR boat — the engine, electronics, metal fittings, and even a mobile phone near the compass can deflect the needle. Unlike variation, deviation is different on every heading.
Deviation is recorded on a deviation card (or table), which shows the deviation for different compass headings. It is determined by 'swinging the compass' — comparing known bearings with compass readings on various headings. Deviation should be small (ideally under 5°) if the compass is properly adjusted.
Key points
- Deviation = compass error caused by the boat's own magnetic field
- Different on every heading (unlike variation, which is constant for an area)
- Recorded on a deviation card for your specific boat
- Minimised by adjusting the compass (placing corrector magnets)
- Keep metal and electronics away from the compass
Continue studying Compass
This topic is part of Module 9. Open the full module for lessons, quizzes, flashcards, and revision tools.