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Comment by zingar | Hacker News Reader

I love me some hulls out of the water but I have a quibble with the term “flying” when there’s still something in the water and taking everything out of the water is dangerous, even of it is only a tiny fraction of the boat… have hydrofoils always been spoken of as flying or is that more recent hype?

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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.

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).

In the context of a planing catamaran, flying refers to allowing the windward hull to lift out of the water in order to minimize wetted surface area. These boats, especially the Hobie 16, were quite popular in the 70s and 80s.

Ha ha, we were taught to keep our optimist bathtubs halfway out of the water when sailing downwind back then. I mostly joke but no one called that flying :).

https://youtu.be/UokOO60dsMU?si=nBMZ4xQFdxIsV6uB

in those wonderful little square boats the reason for tipping the hull was to reduce the amount of weight it surface and dragged through the water. It was still floating, being held above the bottom by buoyancy,so definitely not flying.

Hmmm... apologies for the music.

https://www.youtube.com/watch?v=UokOO60dsMU

yes, yes. I have seen that abomination. Not class legal. lol

It's hilarious though!

The fact that they got it to work is interesting in a way because given the lack of hull length the two surfaces controlling the pitch are right next to each other.

it’s been “flying” as long as I can remember. It’s the distinction between that and floating.

A traditional boat relies on buoyancy to keep it away from the murky depths, while these boats rely on buoyancy only when at rest or going slowly. After that, once the foils take over, they are genuinely flying in that no buoyancy is involved.

But then again, does the word really matter? People refer to “flying” in hot air balloons, too.

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