NorthStar EXPLORER AP380 Installation And Operation Manual page 67

7-3-2 True and apparent wind speed and direction
Apparent wind speed and direction are the values measured on the boat. True wind speed and direction
are the values after allowing for boat speed through the air.
If the boat is moving, then the apparent wind speed is different to the true wind speed and the apparent
wind direction is different to the true wind direction, as shown below.
Boat at rest
True wind speed is the same as apparent wind speed and
true wind direction is the same as apparent wind direction
Boat is at
rest
Boat moving upwind
Apparent wind speed is greater than true wind speed
and apparent wind direction is closer to dead ahead than true wind direction
True
True wind
wind
direction
speed
45º
20 kts
Boat
speed
10 kts
Boat moving downwind
Apparent wind speed is less than true wind speed and apparent wind direction is closer to
dead ahead than true wind direction
True
wind
True wind
speed
direction
20 kts
135º
Boat
speed
10 kts
True
wind
speed
20 kts
Boat
speed
10 kts
Apparent wind
speed 15 kts
Boat
speed
10 kts
Northstar Explorer AP380 System Installation and Operation Manual
Apparent
Apparent
wind speed
wind
28 kts
direction
30º
True
Apparent wind
wind
speed 15 kts
speed
20 kts
Apparent
wind speed
28 kts
Apparent
wind
direction
107º
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