# Computing Desired Winds

```Wind
Lesson Overview
• Wind Terms
• True Wind
• Relative Wind
• Apparent Wind
• Wind Problems
• True Wind
• Desired Winds
• Plotting Wind
2
True Wind
• True direction and speed of wind in
relationship with the earth.
• Ship’s heading and speed does not
affect true wind (obviously.)
3
Relative Wind
• Relative direction and speed of true
wind in relationship to your ship.
• You will always know relative wind.
• Ship’s anemometer will provide this info.
4
Apparent Wind
• True direction and speed of true wind in
• Apparent wind is always on the same
side of the ship as true wind. (i.e. it will
• As ship’s speed increases, apparent
wind moves forward towards the bow.
5
Plotting Wind
• Always referred to as direction FROM
which the wind is coming.
• Plotted in the opposite direction, e.g.
plotted as where is wind going?
Wind vector
Plotted in the
135° direction.
True Wind
315° 15kts
6
Working Wind Problems
• No relative plot.
• Remember wind comes from
somewhere. Plot where it is going.
• Convert relative wind to apparent wind.
7
Wind Vectors
• er vector
• ship’s course and speed
• rw vector
• apparent wind direction and speed
• ew vector
• true wind direction and speed
8
Determining
True Wind
9
Setup
• Information you NEED to know:
• Your course and speed (er vector)
• Apparent wind direction and speed (rw
vector)
10
Determining True Wind
1. Plot your course and speed.
270° 15kts
r
e
11
Determining True Wind
2. Convert relative wind to apparent
wind.
Relative Wind
045°R 15kts
45°
r
e
Apparent Wind
315°T 15kts
12
Determining True Wind
3. Move apparent wind vector to end of
er vector.
r
w
13
Determining True Wind
4. Draw the ew vector from the center to
the end of the rw vector.
e
r
True Wind
going to
202°T 11.5kts
True Wind
022°T 11.5kts
w
14
Computing
Desired Winds
15
Computing Desired Winds
• Information you NEED to know:
• Where do you want the wind?
• True Wind
16
Computing Desired Wind
1. Compute True Wind.
True Wind
022°T 11.5kts
e
w
17
Computing Desired Wind
2. Plot a sample course of 000°.
e
18
w
Computing Desired Wind
3. Plot desired winds. (RW)
W
Desired Winds
30° to port, 20kts
(330°R, 20kts)
R
e
19
w
Computing Desired Wind
3. From the end of the RW line, swing an
arc equal to the speed of true wind.
Desired Winds
330°R, 20kts
True Wind
022°T 11.5kts
E2
W
11.5kt
arc
E1
R
e
20
w
Computing Desired Wind
4. Connect E1W and E2W.
Desired Winds
330°R, 20kts
True Wind
022°T 11.5kts
E2
W
E1
R
e
21
w
Computing Desired Wind
5. Measure angle between 000° & E1W.
Measure speed between E1R.
Desired Winds
330°R, 20kts
True Wind
022°T 11.5kts
57° to
Port
W
E1
10kts
R
e
22
w
Computing Desired Wind
5. Add angle to true wind to get ship’s
course.
Desired Winds
330°R, 20kts
True Wind
022°T 11.5kts
57° to
Port
W
E1
10kts
R
w
e
022
+57
079
Subtract starboard
Ship’s course
and speed
079°, 10kts
23
Computing Desired Wind
6. Do the same for E2W.
Desired Winds
330°R, 20kts
True Wind
022°T 11.5kts
122° to
Port
E2
W
23.5kts
R
e
022
+122
144
Ship’s course
and speed
144°, 23.5kts
24
w
Computing Desired Wind
E2
W
E1
Desired Winds
330°R, 20kts
True Wind
022°T 11.5kts
R
e
r1
079° 10kts
w
r2 144° 23.5kts
25
```