Module 9 of 17
Hand-bearing compass, variation, deviation, and compass conversions.
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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...
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 e...
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 variat...
To convert between True, Magnetic, and Compass bearings, you add or subtract Variation and Deviation. The mnemonic CADET tells you whether to add or subtract: Compass + Add + Deviation +...
A hand-bearing compass is a portable compass used to take bearings of objects. Hold it up to your eye, sight on the object through the prism, and read the bearing from the compass card. T...
A deviation card is a table that records your boat's compass deviation on a range of headings — typically every 15° or 30° around the full 360°. It is specific to your vessel, and must be...
On passage, you must combine variation and deviation to find total compass error. Take variation from the chart compass rose (updating for annual change), then take deviation from your bo...
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