Apparent Wind
This is a short discussion on a phenomenon that is important to keep in mind, no matter what leg of the course you’re on. The breeze you feel in the boat is a mixing of two separate breezes-one which is from the real direction (true wind), and the other, from straight ahead caused by the motion of your boat (generated wind). The product is the apparent wind.
Imagine riding a bike, with the true wind coming straight from the left at 5 mph. When you’re standing still, you feel the force on your left arm. Now ride the bike forward at 5 mph. The wind will feel like it’s coming at you at a 45 angle, between straight in front of you and straight from the left. This is the apparent wind.
As the bike picks up speed, the wind will feel as though it has moved more to the front of the bike. If you start riding down a hill at 45 mph, you won’t be able to feel it from side any more-it’s mostly from the front. That generated wind has taken over.
Conversely, if the bike is going 5 kph and the speed of the breeze from the left picks up to 30 kph, you probably won’t feel the generated wind any longer. You will feel all the true wind, because it is much stronger.
Now, imagine the same situation in the boat. The boat is traveling forward at 5 mph, and the wind is straight across the beam at 5 kph. It will feel as though you are on a close reach, with the apparent wind coming at the boat from a 45 angle. When a puff hits, the wind will move back toward the beam, causing a lift-and when you hit a lull and slow down, the breeze moves to the bow, causing a header. Experiment with this by sailing into lulls and puffs and watching the sidestay tell-tales.