A operator aboard a vessel moving through still air will experience apparent wind, which is from dead ahead and has an apparent force equal to the ship’s speed.
Note: Apparent wind, as measured from a moving vessel, is the force and the relative direction from which the wind blows.
If the actual or true wind is 0, and the speed of the ship is 10 knots, the apparent wind from dead ahead is 10 knots. If the true wind is from dead ahead at 15 knots, and the ship’s speed is 10 knots, the apparent wind is 15 + 10 = 25 knots from dead ahead. If the ship makes a 180 degree turn, the apparent wind is 15 - 10 = 5 knots from dead astern.
Wind vanes and anemometers measure only apparent wind. There is always the problem of converting apparent wind to true wind. There is more than one method of making a wind vector to find the true direction and true speed of the wind. The maneuvering board helps finding speed and direction of the true wind.
Note: You are always in the center of the maneuvering board.
Note: Apparent wind, as measured from a moving vessel, is the force and the relative direction from which the wind blows.
If the actual or true wind is 0, and the speed of the ship is 10 knots, the apparent wind from dead ahead is 10 knots. If the true wind is from dead ahead at 15 knots, and the ship’s speed is 10 knots, the apparent wind is 15 + 10 = 25 knots from dead ahead. If the ship makes a 180 degree turn, the apparent wind is 15 - 10 = 5 knots from dead astern.
Wind vanes and anemometers measure only apparent wind. There is always the problem of converting apparent wind to true wind. There is more than one method of making a wind vector to find the true direction and true speed of the wind. The maneuvering board helps finding speed and direction of the true wind.
Note: You are always in the center of the maneuvering board.
Example: Your ship is on a course of 030° , speed 15 knots. The apparent wind is from 062° , speed 20 knots.
Required: Direction and speed of the true wind.
Solution:
1. Draw the ship’s true course and speed line on the plotting sheet from the center of the board in the direction of the ship’s course (030° ). The length of the line equals the ship’s speed (15 knots) (use the 2:1 scale).
2. Label the center of the plotting sheet "e" for the ship’s true course, and "r" at the end of the ship’s speed line. (This line "er" is one side of the wind vector.)
3. Using parallel rules, measure the direction from which the apparent wind is blowing (062° ).
4. Move this line to the tip of the ship’s course and speed line "r".
5. Draw a line from "r" in the direction the apparent wind is blowing. The length of this line is equal to the speed of the apparent wind (20 knots).
6. Label the end of this line "w." (This line "rw" is the second side of the wind vector.)
7. Draw a line from the center of the maneuvering board "e" to point "w." (This line "ew" is the third side of the wind vector.)
8. Measure from "e" to "w" to find the true direction of the wind.
9. Measure the distance from "e" to "w" to find the true speed of the wind.
Solution: Direction of the true wind is from 109.5° ; speed of the true wind is 10.8 knots.
Note: Measure wind from the direction it is blowing.
Required: Direction and speed of the true wind.
Solution:
1. Draw the ship’s true course and speed line on the plotting sheet from the center of the board in the direction of the ship’s course (030° ). The length of the line equals the ship’s speed (15 knots) (use the 2:1 scale).
2. Label the center of the plotting sheet "e" for the ship’s true course, and "r" at the end of the ship’s speed line. (This line "er" is one side of the wind vector.)
3. Using parallel rules, measure the direction from which the apparent wind is blowing (062° ).
4. Move this line to the tip of the ship’s course and speed line "r".
5. Draw a line from "r" in the direction the apparent wind is blowing. The length of this line is equal to the speed of the apparent wind (20 knots).
6. Label the end of this line "w." (This line "rw" is the second side of the wind vector.)
7. Draw a line from the center of the maneuvering board "e" to point "w." (This line "ew" is the third side of the wind vector.)
8. Measure from "e" to "w" to find the true direction of the wind.
9. Measure the distance from "e" to "w" to find the true speed of the wind.
Solution: Direction of the true wind is from 109.5° ; speed of the true wind is 10.8 knots.
Note: Measure wind from the direction it is blowing.
