Friday, June 15, 2012

Basics of sailing: True and Apparent Wind

In previous post about how to sail I have written how you can stop a sailboat and what do you need to check before you leave the dock. Here I will continue with this manual how to sail.

Apparent Wind and True Wind speed
When the wind is blowing you need to know how strong is the wind to reduce or open the sail safely. It is easy to measure the wind with all the devices on the sailboat because it just measure the direction from where the wind is blowing and how fast the wind the blowing.

When the sailboat is moving the wind get a bit more complex. The wind that we were mentioning before is called True wind. But this is not the wind that we feel on the sailboat (when the sailboat is moving).The wind that is felt on the sailboat is called Apparent wind. Sailboat devices will measure automaticaly what is true wind depending on the apparent wind and the speed of the boat and from where it is blowing.

The easiest way to explain is when the wind is blowing with 20 knots into your front of the sailboat. If the sailboat is moving with 10 knots you will feel only 10 knots blowing from the direction that the boat is sailing. In this case True wind is 20 knots and apparent wind is 30 knots. Direction from where the wind is blowing is the same.

The other example is when the wind is blowing from the back, so the wind is blowing in the same direction that the boat is moving. If the wind is blowing with 20 knots and the boat is moving 10 knots in the same direction True wind is 20 knots and Apparent wind is 10 knots.

If the wind is blowing against the direction where the boat is moving or with the direction the boat is moving the direction of the wind is the same with the true and apparent wind. However if the sailboat is sailing to other directions then against/with the wind the apparent and true wind direction is different.

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