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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 moving upwind
Apparent wind speed is greater than true wind speed
and apparent wind direction is closer to dead ahead than true wind direction
Boat is at rest
True wind speed is the same as apparent wind speed and
true wind direction is the same as apparent wind direction
True
wind
speed 20
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
speed
20 kts
True
wind
speed
20 kts
Boat
speed
10 kts
True
wind
speed
20 kts
Boat
speed
10 kts
Boat
speed
10 kts
Apparent wind
speed 15 kts
Boat
speed
10 kts
Apparent wind
speed 15 kts
True wind
direction
45º
True wind
direction
135º
Apparent
wind
direction
107º
Apparent
wind
direction
30º
Apparent
wind speed
28 kts
Apparent
wind speed
28 kts
Boat at rest