Thursday, June21, 2018

Determining the True Wind Speed

Either use a wind meter like this.
Or estimate using the sea state ie. white caps, sound of the wind in the rigging as discussed HERE.

If you are using a wind meter you can estimate the true wind speed by sailing close hauled and subtracting 80% of the boat speed from the apparent wind reading of the wind meter. That will get you very close. For example, if the apparent wind is 20 knots and the boat is going 6.2 knots at 45 degrees to the true wind then the true wind is 20 - 6.2 + 1.2 = 15 knots. The calculator says 15.1, which is close enough.(I used True Wind Speed = Apparent Wind Speed - Boat Speed + .2 * Boat speed rather than Wind Speed = Apparent Wind Speed - .8 * Boat Speed because the math is easier to do in your head).

You can use the calculator and plug in realistic values for your own boat and come up with some guidelines.

The important thing is to write down the actual apparent wind readings when you are collecting data. Then when you have your target boat speed and target apparent wind direction, you can use the boat speed tool to give you a table so that you can read off apparent wind speed and find your target boat speed.

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