When heeled, the vane axis tilts so the athwartship wind component
is reduced by cos(heel). Both AWAm and AWSm read too small.
atan2 form handles all AWA quadrants (including downwind > 90°).
Leeway & Course Through Water
LWY = K · heel / STWm²
CTW = HDG + LWY
STWc = STWm / cos(LWY)
K ≈ 9–16 for typical sailboats.
The signs of LWY and Heel are the opposite to sign of AWA.
STWc is the actual track speed; the knotmeter reads the centerline component.
True Wind (relative to water)
TW = AW − BWwater
BW = (STWm, HDG) [col 1&2]
BW = (STWc, CTW) [col 3]
TWA = angle of TWD off bow ( col 1&2)
TWA = angle of TWD off CTW ( col 3)
AW absolute direction: AWD = HDG + AWAm [col 1],
AWD = HDG + AWAc [col 2&3].
Note: AWD uses HDG (not CTW) because the sensor is on the mast,
oriented to the centerline.
Current, Ground Wind & Height
Current = BWground − BWwater
GW = AW − BWground
BWground = (SOG, COG) [all cols]
GWS10 = GWS · (10/H)α
Ground wind (GW) is independent of leeway because SOG/COG and
corrected AWD do not depend on how the boat tracks through the water.
GWS10 adjusts to 10 m reference height; α ≈ 0.11 (open sea).