# I Calculating Apparent Wind

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1. Mar 26, 2016

### Neeps

Hi. I'm working on a digital filter, whose computations are dependent on calculating apparent wind. But i'm not entirely sure if i'm using the formula correct, because i find the description of variables some what vague. Would love if someone please could point out, what the alpha angle is representing on this page :
https://en.wikipedia.org/wiki/Apparent_wind

I am assuming that α = pointing angle, is true wind angle relative to the boat.
Would that be correct? Thank you for any answers, and sorry if this might be wrong forum to post this thread.

2. Mar 26, 2016

### tech99

Alpha is the angle between the vessel's motion and the wind. But strictly speaking it is not the pointing angle, because a vessel does not generally move exactly in the direction it is pointing due to leeway. The latter is the tendency for a craft to move sideways due to the lateral force of the wind upon it. Leeway is similar to glide angle for an aeroplane, and is related to the behaviour of the keel, rudder and hull as an under water wing.

3. Mar 26, 2016

### Neeps

By that definition, my assumption would be correct, yes? True wind angle would be where the wind hits the boat, relative to the bow, ignoring the actual motion of the boat. Apparent wind angle would be where the boat actually feels the wind coming from, because of motion.

4. Mar 26, 2016

### tech99

This is getting confusing. Normal
Your assumption is not correct because alpha is the angle the wind makes with the vessel's motion rather than the vessel's centre line. In practice, it may be a negligible difference, but to be strictly correct it is best to measure vessels motion and true wind relative to True North.