SailNet Community banner
1 - 6 of 6 Posts

·
Registered
Joined
·
191 Posts
Discussion Starter · #1 ·
Hello
is there a formula that can figure apparent wind direction to true wind direction. also for speed of wind. with the sailboat going 6 knots at a 45 degree angle to a 15 knot wind apparent on the boat - what would be the true wind angle an speed? i'm not a racing sailor but a cruiser with curiousity.
thxs!
 

·
Spam, Food of the Seagods
Joined
·
212 Posts
This all I know.

True-Wind Calculator Formulas
** Apparent-Wind (AW) and Apparent-Wind Degrees off the bow (D) are known. }

Y = 90 - D
a = AW * ( cos Y )
bb = AW * ( sin Y )
b = bb - BS
True-Wind Speed = (( a * a ) + ( b * b )) 1/2
True-Wind Angle = 90-arctangent ( b / a )

Apparent-Wind Calculator Formulas
** True-Wind (TW) and Apparent-Wind Degrees off the bow (D) are known. }

Y = 90 - D
a = TW * ( cos Y )
b = TW * ( sin Y )
bb = b + BS
Apparent-Wind Speed = (( a * a ) + ( bb * bb )) 1/2
Apparent-Wind Angle = 90- arctangent ( bb / a )

True and Apparent Wind Calculator
 

·
Registered
Joined
·
2,318 Posts
In practical terms the tricky part is knowing your apparent wind angle without a vane and gauge that give you the angle. Speed is simple now with GPS, and true wind is easy to find old-school if you just shoot into the wind briefly while watching your compass.

If you're trig-challenged like me, but know true wind and speed, and boatspeed, then you can do a qick pencil plot an a chart and just measure the long AW line.
 

·
Registered
Joined
·
21 Posts
Slight change:
True-Wind Speed = (( a * a ) + ( b * b )) 1/2
should be
True-Wind Speed = (( a * a ) + ( b * b )) ^1/2
i.e. it's the square root of the sum of the squared sides, the Pythagorean Theorem.
Same for the formula for Apparent-Wind Speed.
 
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top