1. Navigation
NAU 102
Lesson 33

2. Measures apparent wind direction. Measures apparent wind speed.
Weather Instruments
Wind Vane
Measures apparent wind direction.
Anemometer
Measures apparent wind speed.

3. Weather Instruments
Wind Vane
Anemometer

4. Wind
Definitions
True wind. The speed and direction from which the wind blows with reference to a fixed point.
Apparent wind. The speed and direction (true or relative) from which the wind appears to blow with reference to a moving point.

5. Wind Examples True wind: East wind, 10 knots.
Ship: course 090° T, speed 5 knots.
Apparent wind: From 090° T (000° R), 15 knots.

6. Wind Examples True wind: West wind, 10 knots.
Ship: course 090° T, speed 5 knots.
Apparent wind: 270° T (180° R), 5 knots.

7. Wind Anemometers and wind vanes give apparent wind
(unless the vessel is stopped).
We must solve for True wind for our weather observations.
Best done graphically on maneuvering board, plotting sheet or compass rose.

8. Wind
Example 1: A ship is proceeding on course 240° at a speed of 18 knots. The apparent wind is from 040° relative at 30 knots. What is the true wind?

9. Step 1: Plot ship’s course & speed.
Wind
Step 1: Plot ship’s course & speed.

10. Wind
Example 1: A ship is proceeding on course 240° at a speed of 18 knots. The apparent wind is from 040° relative at 30 knots.
Step 2: Convert relative direction of apparent wind to true direction, if necessary.
R + S = T
040° R + 240° = 280° T

11. (Remember, draw the direction the wind is blowing towards!)
Step 3: Draw the apparent wind from the tip of the ship’s course & speed vector.
(Remember, draw the direction the wind is blowing towards!)
Wind

12. Step 4: Complete the triangle. Result = True wind.
Direction = 315 °T
Speed = 20 knots

13. Wind
Example 2: A ship is proceeding on course 140° at a speed of 15 knots. The apparent wind is from 110°T at 20 knots. What is the true wind?

14. Step 1: Plot ship’s course & speed.
Wind
Step 1: Plot ship’s course & speed.

15. True direction of apparent wind = 110° T
Example 2: A ship is proceeding on course 140° at a speed of 15 knots. The apparent wind is from 110°T at 20 knots. What is the true wind?
Step 2: Convert relative direction of apparent wind to true direction, if necessary.
True direction of apparent wind = 110° T

16. Step 3: Draw the apparent wind from the tip of the ship’s course & speed vector.

17. Step 4: Complete the triangle. Result = True wind.
Direction = 071 °T
Speed = 11 knots

18. Wind Measurement Beaufort Scale
If no instruments are available, speed may be estimated by observing the effect on the water.
Scale was devised in 1806 by English Admiral Sir Francis Beaufort ( ).

19. Force 0

20. Force 1

21. Force 2

22. Force 3

23. Force 4

24. Force 5

25. Force 6

26. Force 7

27. Force 8

28. Force 9

29. Force 10

30. Force 11

31. Force 12

32. Introduction to Navigation
Questions?