Moving your ‘hole in the water’

There is an old saying that a boat is a hole in the water into which you throw money! That may be more accurate than you think. The wake behind any boat is evidence that a large amount of water is being displaced by simply moving the boat. Shoving all that water out of the way takes a lot of energy, generated from a lot of increasingly-expensive diesel fuel. So ask yourself, “How much do I have to pay to move my hole in the water?”

The faster you go, the more expensive it is. Would you like to reduce that cost? The trick is to reduce the amount of water you have to shove out of the way in order to move your “hole in the water.” How do we do that? Simple! We raise the hull of the boat out of the water as much as we can. A boat that isn’t in the water doesn’t have to move as much water just to move. The key to doing that is to add hydrofoils, that is, small wings under the water that provide lift, raising the hull above the waves. With only the small hydrofoils shoving water out of the way, the boat can go ever-so-fast, while saving a bundle on moving your hole in the water. And it works on big boats as well as small ones. It’s like running a fully loaded ship for the cost of an empty one. Now, get out your calculator and add that one up.

OK, so where do we find hydrofoils way out here?

Hydrofoils are actually very popular. You see them all over, it’s just that people generally don’t recognize one when they see it. Yet, people all over the islands buy them, even though they never actually use them. And, since they never really do anything, but everyone has to have one, they must be “Macho Toys.” You know, just for looks.

Have you figured it out yet?

It’s a spoiler! You know, those little upside down airplane wings they put on the back of cars to make them look like race cars. Obviously, on an island with a top speed of 45mph they must be only for looks, because they have to be going 80 before they do anything.

Water is denser than air. So a wing of a given size will provide more lift in water than in air, and at a lower speed. You could simply put a single hydrofoil under the boat (upside down from the way a spoiler is mounted on a car,) and raise up the hull. However, it may also become mechanically unstable if you raise the boat completely out of the water. So, the boat may simply fall over.

Just as a table needs three legs to keep it from falling over, three hydrofoils will make the craft more stable. Two can be mounted about a third of the way back from the bow, and off to the sides like adjustable outriggers, but down in the water just a few inches below the bottom of the boat. The third one is placed aft, below the rear of the boat.

To make the configuration practical, the angle of attack—that is, the angle at which the foil moves through the water—needs to be adjustable on all three foils independently. If the foils aim down into the water, the craft will be pulled down (obviously the wrong direction,) while raising that angle will bring the bow up out of the water. But if you bring it up too much, the foils may come out of the water, or simply bring the craft to a halt. So they need to be adjusted for optimum speed while going.

Now, the aft foil needs to control the level of the stern so that the propellers don’t come out of the water. They don’t work well in air. Not to mention that it is bad for your outboard motor to be running out of the water. But the stern can be raised up just enough so that it skims along the surface making very little wake.

It will take some practice, but you can do it, if you really want to save money, and have more fun moving your hole in the water.

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To learn more about how things work, read the exciting e-book, Resonant Fields, the Fundamental Mechanism of Physics, Made Easy To Understand. It’s available online at www.coolscience.info. Click on “Intelligent Design.” © 2005 by CoolScience