Tuesday, November21, 2017 L-36.com

Determining the True Wind Speed



Either use a wind meter like this.
polarsmeter
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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The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerious of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.