But that's not what I want to talk about. Instead I want to discuss winged keels. I mean what is the big deal, after all? Sure, they're modern, sure they're cool, and "every boat must have one". But why, exactly?
It's all about end effects.
OK, now I have to build something in your mind here. Please give me some latitude and play along... Imagine an airplane wing. Regardless of which theory you consider to describe how it holds the airplane up in the air, all the theories condense to the singular fact that there is lower pressure on top of the wing than on the bottom. The airplane is held up by suction. So what keeps the high pressure air under the wing from just flowing up into the low pressure area above the wing? Well, on the leading and trailing edges of the wing, it is momentum - that wing is moving right along, and the air at the front and rear of the wing just doesn't have a chance to flow "upstream" to the low pressure area.
OK. So enough about airplanes... but hold that thought. The keel of a sailboat is amazingly similar to an airplane wing. It is "flying" thru the water, and is required to provide lift, to keep the boat from sliding downwind. The analogy is really very good. So then, what keeps the water from flowing over the bottom end of the keel, from the high pressure side to the low pressure side? Nothing...
The design is so effective that significantly less ballast is required, the force being replaced with more effective lift. Thus the weight of the keel can be reduced. And the wings serve as a good place to stash lead, down there at the very bottom of the keel, so the draft of the keel can be reduced. And then, since everything in nautical design is connected to everything else, the wetted surface of the boat is decreased because less total weight is being carried. And the boat goes faster.
It really is a good idea.
So then why then did winged keels take so long to appear?
See the First and Second Corollaries of Salnick's First Law.