||The angle of sail is the difference between the direction your boat is heading and the direction of the wind. Different angles of sail, called points, change as your boat changes course, and the sails must be adjusted to harness the wind as efficiently as possible.
When sailing as close to the wind as possible, with the sails trimmed in all the way, you are close-hauled or beating. As you bear off, steering away from the wind, you will ease your sails as you sail onto a close reach, then a beam reach (where the wind is blowing ober the side, or beam, of the your boat), then a broad reach.
When you are sailing directly away from the wind, you are sailing on a run with your sails eased all the way out. If you continue to turn, you will gybe, so that you are on a run with your sails on the opposite side of the boat. As you gradually head up, turning toward the wind, you will need to trim your sails to keep them from luffing (flapping in the wind) as you sail onto a broad reach, then a beam reach, close reach, and finally back up to close-hauled.
Wind is the movement of air from areas of high pressure to areas of low pressure. While air is made up of gases, in many ways it behaves like a liquid. It flows over and around obstructions, seeking the path of least resistance. Wind will blow more strongly out of valleys and be almost nonexistent on the leeward side of a high hill.
The wind is rarely perfectly steady. Depending on the surfaces it passes over, the stability or instability of the air, weather systems, and even the effects of other boats, the wind is constantly changing in both strength and direction.
The wind is invisible, but its effects are not. When you're sailing, it's important to be aware of the strength and direction of the wind in order to harness its energy efficiently and sail safely.
There are many ways to rell the direction of the wind. Wind blowing across water causes friction on the surface, forming small ripples perpendicular to the direction of the wind. (Larger waver are caused by the longer-term effects of the wind and current.) Learning to determine the wind's direction by looking at the water's surface takes much practice, but it's the most accurate method. Other heopful indicators are flags, smoke, and other sailboats.
There are a couple of simple tools that can help you find the direction of the apparent wind. Telltales are lengthsof yarn or strips of nylon tied to the shrouds and backstay. A masthead fly, with a wind arrow, goes at the top of the mast and points into the wind.
You can also use your sails to find wind direction. When you ease your sails, they will luff and line up with the wind. Gradually turn your boat towards the wind; you'll be straight head-to-wind when the sails are luffing on the boat's centerline.
One telling indicator of wind strength is when whitecaps (white tufts on the waves) just begin to form. This occurs at around 12 to 14 knots, a point at which many small boats begin to get less stable. Inexperienced sailors shouldn't be out alone when there are whitecaps.
Apparent Wind and True Wind
True wind is the wind strength and direction you'd feel if your boat were standing still. Apparent wind is the combination of the true wind and the wind caused by your boat's movement (boat-speed wind).
Imagine sticking your hand out of a parked car and feeling a lighty cross-wind. As the car accelerates, you will gradually feel more and more wind coming from the front of the car even though the "true wind" is from a 90 degree angle.
The same phenomenon occurs when you're sailing. An anchored boat might feel 10 knots from the north, while a boat sailing will feel the apparent wind more toward its bow. A boat sailing close-hauled toward the wind will feel a much stronger apparent wind than a boat sailing on a broad reach, even though they are in the same true wind.