Hacker News Reader

They call it flying because foils are flying through a medium, generating lift, just as the wings of airplanes do.

A big difference is that these wings lift the main body out of that medium (water) into a much less dense one (air), hugely decreasing resistance.

And yes, this doesn’t lift the boat completely out of the water, but airplanes do not get completely out of the medium they use (air), either.

View on HN

Interesting point about not moving out of the medium. I don’t think this is terribly important but you could say that the airplane completely moves from the medium of wheels on the ground into the less dense medium of air.

The important distinction is that you can not fly in anything that doesn't get out of the way as you move through it.

So the 'wheels on the ground' don't have anything to do with flight (though technically they are also in the air). Flight takes place in a medium. For a plane that is only one medium unless you're looking at a flying boat at take-off, for a sailing vessel there are two, there is the water (dense, slow to push out of the way so high drag) and the air (much less dense, so faster to push out of the way, much lower drag).

Reply on news.ycombinator.com