Module 9 of 17
Compass
Hand-bearing compass, variation, deviation, and compass conversions.
Three Norths
To understand compass work, you need to know there are three different 'norths'. True North is the geographic North Pole — all charts are aligned to true north. Magnetic North is where a magnetic compass needle points, which is not quite the same place due to the Earth's magnetic field. Compass North is where your boat's compass points, which may differ from magnetic north because of local magnetic influences on the boat.
Key Points
- True North — geographic north (charts are drawn to true north)
- Magnetic North — where a compass needle naturally points
- Compass North — where YOUR boat's compass points (includes deviation)
Variation
Variation is the angular difference between True North and Magnetic North. It changes slowly over time and varies by location. On a chart, variation is printed on the compass rose — for example: 'Var 2°W (2020)' means that Magnetic North is 2° west of True North, and this was correct in 2020.
The annual rate of change is also given (e.g., 'decreasing 8' annually'), so you can calculate the current variation. In UK waters, variation is typically around 1–3° West.
Key Points
- Variation = difference between True North and Magnetic North
- Found on the chart compass rose with date and annual change
- UK waters: typically 1–3° West (slowly decreasing)
- Apply variation to convert between True and Magnetic bearings
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