I knew someone would make this comment. I love HN for this kind of pedantry when it's specific, accurate and doesn't dismiss the entire article for one inaccurate analogy.
The polar diagram shown there is what should replace the ellipse in TFA. It's far more complicated than a simple geometric shape since it has to account for such practicalities as sail inventory.
I also knew that someone was going to comment the the beam reach was not necessarily the fastest.