Why Does Your Foil Actually Fly
In 1997 I earned a degree in physics from the University at Buffalo. Since then I've spent 3 decades studying physics and biophysics recreationally. I'm not a scientist, but I am very curious, and I have a passion for learning about nature. As a physics student we learned that airplanes, and our hydrofoils, fly because of Bernoulli's Principle. It basically says that when a fluid moves faster (or when an object moves through a fluid faster) the pressure is less. So, if a foil is curved on top and flat on the bottom then the water has to move faster on the curved top part of the foil and thus the pressure will be less on top of the foil than the bottom. The foil will rise because of this difference in pressure. Well, I think that's a bunch of bullshit. Airplanes fly upside down too. According to Bernoulli's principle they should plummet to the ground if upside down. Plus, it still doesn't give us any idea of what the actual force really is that is keeping the foil up. There are only four forces in the universe: the strong nuclear force, the weak nuclear force, the electromagnetic force, and the gravitational force. Bernoulli's principle doesn't give us any clue as to which of those forces is actually at play. Common sense would have us think that it's probably not gravity that makes a foil fly because gravity does the opposite....it pulls it down. It's also probably not the strong or weak nuclear force because those are forces acting within the nucleus of atoms, not between foils and water. So, maybe it has something to do with electricity or magnetism.
It turns out that the answer is electricity. Yep, your foil flies electrically. Specifically, triboelectricity. What is triboelectricity? Some materials, like air and water, have a very high ability to acquire positive charge. Other materials, like metal and prepreg carbon, have a high ability to acquire negative charge. And the separation of these positive and negative charges happens through friction. You know the effect of rubbing a balloon on your head. Air has a very high ability to acquire positive charge, so when you rub a balloon on your head the friction separates charge, and the air gets the positive charge while the balloon gets the negative charge. Now think of the massive friction of a metal airplane wing moving through air at 400mph. The air acquires massive positive charge while the metal wing of the airplane acquires negative charge. Metal is good at acquiring negative charge, while air is good at acquiring positive charge. The Earth is also negatively charged, so the plane flies because the negative electric charge of the Earth is repelling the negative electric charge of the airplane wing. Remember from eighth science class that like charges repel each other. Water also has a very high ability to acquire positive charge, while your carbon foil wing has a high ability to acquire negative charge. The negative charge of your foil then repels the negative charge of Earth.
Now you might thinking that electric charge cannot be that powerful. Well you're wrong. Richard Feynman, arguably the greatest physicist of the 20th century, proved this. He proved it through a simple thought experiment that has been verified through real measurements. Imagine two people. You remove 1% of the electrons (negative charge) from each person. Just 1%. Now each person has a net positive charge since you removed electrons, so the two people will repel each. You lay one person on the ground, and you put the other person on top of them. They will repel each other. How much weight would you have to put on top of the top person to keep him 1 meter apart from the bottom person without him being pushed up into the air? The answer is a weight equal to the weight of Earth. That is the enormous strength of electrical repulsion. The electromagnetic force is 10^36 times stronger than the gravitational force. It's the second most powerful force in the universe. That's why your foil flies. Electric force.
So your sail, or your hand-wing, or your kite, or a tow line from a boat, or your paddle, or a wave, or a Foil Drive motor, or your leg pumping action, is giving you enough friction between the foil and the water to generate enough negative charge on the foil wing to repel the negative electric field of the Earth and this gives you lift. That's the real reason your foil flies. Forget Bernoulli's principle. Universities still teach that it's Bernoulli's principle, but that never tells you what the actual force really is. It's electric force. That's why airplanes can fly upside down.
