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

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. Why is it different than true north?
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 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. 025o M 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 (+)