What is a "keel" and how does it affect the faceting pattern?

[Dee*Jay]

I've been mulling over different faceting patterns in oval diamonds and I've found some that seem to be cut almost on an X/Y axis (kinda like if you turned a princess 45 degrees) rather than with elongated facets as though a round had been "stretched." Is it possible this X/Y faceting is due to a "keel"? If so, what is a keel? How common are then? Can I ask for a jeweler to find me an oval specifically with a keel?

GemKlctr's "big blue" diamond is the best representation I can find of what I'm trying to describe. Check out the fourth picture down in particular. https://www.pricescope.com/community/threads/my-big-blue-diamond.34921/

(GemKlctr, hope you don't mind me posting a link to your thread.)

Thank you all for putting up with my obsessive oval questions!!! I promise some day I will indeed find a new stone...

P.S. - If this faceting pattern is not due to a "keel" can someone please tell me what might be causing it. Thanks!

 

[Gemklctr]

Of course I don''t mind. I''m interested in the question you raise too. Any cutting pros out there have something to add?