If you go to YouTube, you can find some amazing hydrofoil videos. Like this one:

Or this:

The technology works with Navy-size ships as well:

This sailboat is able to reach 47 knots by flying on hydrofoils:

The technology even works in a kayak:

So what is going on here? There are two things to understand. First, water as a fluid is a nearly a thousand times denser than air (a liter of air weighs about 1.2 grams, while a liter of water weighs 1,000 grams). That density means that a boat’s hull creates a huge amount of drag. Second, because water and air are both fluids, the idea of a wing works just as well in water as it does in air. But because water is so much denser, a very small wing generates a huge amount of lift.

Combining these two ideas, you end up at the hydrofoil. A hydrofoil is a small underwater wing that lifts the hull out of the water to eliminate its drag.

If you want to get into the math of hydrofoils, this page is helpful: How a hydrofoil works

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