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Nautical Navigation

Lesson III: Three Norths & Variation Preserving America’s Sailing Legacy * Engaging Sailing’s Next Generation. Nautical Navigation. Three Norths. Grid North True North Magnetic North. Grid North. Refers to the direction northwards along the grid lines

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Nautical Navigation

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  1. Lesson III: Three Norths & Variation Preserving America’s Sailing Legacy * Engaging Sailing’s Next Generation Nautical Navigation

  2. Three Norths • Grid North • True North • Magnetic North

  3. Grid North • Refers to the direction northwards along the grid lines • The difference between grid north and true north is very small and can be ignored for most navigational purposes

  4. True North • The north pole around which the world rotates • Where the lines of Longitude intersect • Also known as “geographic north”

  5. Magnetic North • Where the needle on a magnetic compass points Why is it different than true north?

  6. Magnetic North • Magnetic North is different than True North because of the magnetic field generated by the earth’s molten core • Magnetic field created by the constantly moving nickel iron fluid in the earth’s outer core • Does Magnetic North stay the same? NO! Moves ~ 25 miles/year

  7. Magnetic North is Constantly Changing

  8. Variation • Also known as “magnetic declination” • The difference between True North and Magnetic North • Variation

  9. Variation • A compass rose on a chart or map is used to measure the difference in variation • Look at your charts and find the compass rose Why does this matter to you as a navigator? • Outer Ring = True North • Inner Ring = Magnetic North

  10. Variation • When converting True degrees => Magnetic degrees • “West is Best” (+) “East is Least” (-) • Example: • You are sailing offshore. You look at your chart and see that you want to steer 015o T • The Variation on the chart is 10o W • What course would you steer using a Magnetic Compass? • 025o M

  11. exercise • Complete the following worksheet on variation calculations • Remember… • [Magnetic Bearing] = [True Bearing] + [Variation] • If the variation is East, subtract (-) • If the variation is West, add (+)

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