Projected plane area?

Ok for a sail on a sailboat you need two things:

• Calculate the actual area that the sail has.

• You also need the normal vector of the sail. So the vector that is perpendicular to the surface of the sail.

Now all you have to do is this:

 float affectedArea = sailArea * Mathf.Abs (Vector3.Dot(windDir, sailNormal));

Note that windDir as well as sailNormal need to be normalized vectors (vectors with a length of 1.0). If your sail is a gameobject you can simply get the normal from one of the local axis vectors (forward, right, up) which are already normalized. Just pick the right one. sailArea is just a float value which should be equal to the area of your sail.