I don't know much about sailing, but I was just wondering what kind of
keels the old sailing ships had (like the Mayflower). Did they have a
distinct keel, or was it just more like an extension of the hull?

I looked at some model ship images, and it doesn't look like there's
enough of a keel to prevent the ship from slipping sideways.
http://www.handcraftedmodelships.com...model-ship.php