True wind/apparent wind?
Can anyone give me the formula fore calculating:
1: true wind, when you know apparent wind and boatspeed? (speed and angle)
2: apparent wind, when you know true wind and boatspeed?
If possible on a exel file...? ;-)
(General) Thanks to everyone that contribute in this forum !
Taking the angle between the boat's heading and the direction the wind is coming FROM,
first get the longitudinal (x) and lateral (y) components of the wind velocity:
(V means speed, a means apparent, t means true)
(A means angle in DEGREES)
Vay = Vtrue*sin(3.1416*Atrue/180)
Vax = Vtrue*cos(3.1416*Atrue/180) + Vboat
Vapparent = square root of (Vax squared + Vay squared)
Aapparent = (180/3.1416)*arctan (Vay/Vax)
To go the other way, switch true and apparent everywhere, and put a minus sign in the Vx equation:
Vty = Vapparent*sin(3.1416*Aapparent/180)
Vtx = Vapparent*cos(3.1416*Aapparent/180) - Vboat
Vtrue = square root of (Vtx squared + Vty squared)
Atrue = (180/3.1416)*arctan(Vty/Vtx)
(Im a bit tired now, it's 23.59 here)
I'll have a closer look tomorrow, if not anybody can have a look and help me in the mean time?
I put this sheet together quickly a couple of years ago. Seems about right until App Angle >90. I just input your calc in RED. Doesn't seem to work. Maybe someone can check both calcs.
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