How does sailing work, in general?

Let's take a step back from the AC, and get a bit into how a boat moves using only the wind. Today's racing boats are the result of literally thousands of years of research into materials, sails, hydrodynamics, equipment and meteorology.

A common misconception is that sailboats are "pushed" by the wind. While occasionally there is some truth to this, the way a sailboat moves is in fact much closer to how an airplane wing works. Without stepping into DRC/CEJ dork-territory, picture an airplane wing...when it goes through the air, the pressure differential creates a force ("lift") that "pulls" the wing up...and the airplane is attached to that wing. Now take that wing, and rotate it so that the part that was atttached to the plane is now attached to the boat. If you cause the wind to go acros this wing/sail, it will cause a similar pressure differential, and "lift" the sailboat forward. The offshoot of this is that you are now able to have the boat travel in the direction opposite to the wind. This is called beating; when a sailboat is going in the same direction as the wind, that is called running.

However, no sailboat can ever go directly into the wind - the airplane wing doesn't work if you rotate it 90 degrees from its normal orientation. When a boat is pointed directly into the wind that is called being "in irons" or "dead into the wind". As a boat tries moves away from irons, it is able to travel faster and faster. This provides an interesting situation in a race; if the course is set up so that you would want to travel directly into the wind (also called sailing "upwind" or just "up", you have to choose between traveling more directly towards your goal at a slower speed, or less directly toward your goal at a higher speed. This leads to the concept of velocity made good ("VMG"); VMG is the rate at which you are approaching your goal. If you are moving 10 mph directly towards your goal, you are making 10 VMG. If you are traveling at a 45 degree angle to your mark, you are making about 7 VMG. If you are travelling at a 90 degree angle to your mark, you are making 0 VMG. The goal in a sailbody race is to always maximize your VMG.

For each boat, there is an angle to the wind for which if you move slightly closer your speed begins to drop dramatically. Generally, if you are trying to sail directly into the wind, you want to point the boat at this angle. This is called sailing "close-hauled", in most boats, it is 30-40 degrees away from irons. Clearly, even sailing close-hauled you will never get to a point that is directly into the wind. Because of this, the boat will have to zig-zag up the race course. The act of the bow of the boat crossing the direction of the wind is called a tack; when the stern of the boat crosses the wind, that is called a gybe. Tacking and gybeing both require switching the sails from one side of the boat to the other. If the sails are on the left ("port") side of the boat, the wind is coming over the right ("starboard") side; this is called being on starboard tack. Similarly, if the sails are on the starboard side of the boat, that is the port tack.

We can now describe a full 360 degree turn. Starting out in irons, turning the boat to starboard puts you on a port beat. Contintuing, when the wind is coming directly over the side, that is a port reach, then port run. When the wind is at your back, that is a dead run; continuing the turn to starboard you pass through starboard run, starboard reach, starboard beat and then back into irons. Each of these terms is called a point of sail.

That's enough for today - next time we'll take look around an America's Cup Class boat.