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The true-wind is the apparent wind which you feel when you are not moving, for example at anchor.  The apparent-wind is the wind direction and speed which you feel while the boat is moving.  The apparent-wind is forward of the true-wind (except when it is directly forward or behind the boat).  In a close reach, the apparent-wind is forward and is stronger than the true-wind.  In a deep broad reach, the apparent-wind is forward and is weaker than the true-wind.
  

  
True-Wind
Calculator
   
           
1
.  Enter the Speed in knots of the Boat
(actual speed as read on a GPS ): 
 

2.  Enter the speed in knots of the
Apparent-Wind:
 

3:  Enter the angle of the
Apparent-Wind to the boat:
 


 

  
Apparent-Wind
Calculator
   
           
1
.  Enter the Speed in knots of the Boat
(actual speed as read on a GPS ): 
 

2.  Enter the speed in knots of the
True-Wind:
 

3:  Enter the angle of the
True-Wind to the boat:
 


 

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 = 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 = arctangent ( bb / a )
  

   

  The values determined from this calculator should be used for educational purposes only.  This calculator should not be used in determining the suitability of purchase, charter or passage on a boat.  Instead the manufacturer should be contacted to obtain the boat's characteristics.  The results of this calculator should not be relied upon for navigational purposes.  US SAILING and its members assume no liability for the information presented on this website.  The user is responsible to check the validity of all information.

Copyright 2002          Web page last updated 05/11/2005