Monday, May21, 2018

True Wind Direction Chart Help

For this discussion I have created a reduced chart so we can focus on one example.


We read the apparent wind as 17 knots. Our example boat has the following boat speed vs apparent wind angle:

Our goal using this chart is to sail at 45 degrees to the true wind. To start, we are going to sail at 6.5 knots. Looking at our example boat we see that the boat is sailing at an apparent wind angle of 34 degrees which we read off the masthead fly.

We look at our chart and see that at 6.5 knots in 17 knots of apparent wind we should be pointing 29 degrees apparent and we are way off that so we need to head up. We head up and the boat slows down to 5.5 knots. After letting things settle down we read the apparent wind angle and see that it is 28 degrees. Out chart says that at 5.5 knots we should be at 32 degrees to the apparent wind so we are pinching. Now we try 6 knots. At that boat speed, the apparent wind angle is about 31 degrees and we see from the chart that the entry for 6 knots boat speed at 17 knots apparent wind is 31 degrees so we know we are now heading at 45 degrees to the true wind.

Ad by Google

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 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 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.