Apparent Wind versus True Wind

When reading a telltale, you need to keep in mind that it shows the

direction of the apparent wind as distinguished from the true wind—

a distinction that is fundamental to small-craft navigation. The apparent

wind is the combination of the true wind over the water and the effective

wind generated by the motion of the boat.

The difference between the directions of the true wind and the apparent wind depends on how fast you are moving relative to the true wind speed. For boat speeds less than 10% or 20% of the true wind speed, the difference is

negligible, and you can read the true wind direction directly from the telltale.

When you are moving, the direction of the true wind is always aft of the apparent wind. If the apparent wind is on the beam, you must face this apparent wind and turn aft to look in the direction the true wind comes from. This is true regardless of your point of sail. If the apparent wind is 45° on the bow, the true wind is closer to the beam. If the apparent wind is on the quarter, the true wind is closer to the stern (see Figure 1-2).

Figure 1-2 True wind direction versus apparent wind direction. The true wind is always aft of the apparent wind. The difference between wind directions is largest when the wind is on the beam (far left). Each boat is moving 6 knots (S = boat speed) in a true wind of 10 knots. The resulting apparent wind speed (AW) is shown for each boat as well.

STEERING BY THE STARS

Stars are a part of our environment we can rely on, no matter where we are.

In the Arctic or the desert, or at sea a thousand miles from land, when you spot familiar stars, it is like meeting dependable friends. It is comforting in any circumstance to recognize part of our environment, to at least have our bearings. With this attitude in mind, it helps to get to know our friends’ names and occasionally look for them, even when we don’t need them.

Дата добавления: 2015-11-16