**Simple Geometric Calculation**

**Y = 90 – D**

a = AW * ( cos Y )

bb = AW * ( sin Y )

b = bb – BS

True-Wind Speed = (( a * a ) + ( b * b ))

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 )**True-Wind Calculator**

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

**http://www.sailingusa.info/true_wind_calculator.htm**

This simple calculation doesn’t take into account **leeway**. Leeway is the drift of the boat to the side due to the push of the wind against the sails.

Leeway depends on:

- Angle to the Wind – is greatest on a close reach and zero on a run.
- Velocity of the Wind
- It will be different for every boat.

This simple calculation doesn’t take into account **current**. Current creates a ‘water frame of reference’ which is different from the ‘earth frame of reference’

Earth Frame:

- GPS

Water Frame:

- Paddle Wheel Speedometer
- Wind Vane
- Anemometer

*Current Deviation*

**C : Is the angle of the Current to Boat’s Bow**sine C = c/ac = sine C * a

cosine C = b/a

b = cosine C * a

d = power – b

CD = arctangent ( c/d )

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