True And Apparent Wind Speed And Direction - NorthStar Pilot System NS3300 Reference Manual

Reference Manual
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 20
45º
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
Apparent
wind
wind speed Apparent
speed
wind
28 kts
20 kts
direction
30º
Boat
speed
10 kts
Apparent wind
speed 15 kts
True
Apparent wind
wind
speed 15 kts
speed
20 kts
Boat
speed
10 kts
Apparent
wind speed
28 kts
Apparent
wind
direction
107º
37