Originally Posted by noelex 77
If we know the apparent wind speed and direction and STW we can calculate true wind.
So for the purposes of data collection AWS, AWA and STW are all that sailors need to report. True windspeed data is not needed. Given the ease of calculating true wind its superfluous, unnecessary information.
You're right, but let me point out some of the difficulties in converting apparent wind to true:
To be more accurate we also need to know leeway before we can convert AWS/AWA/STW to true wind (water-referenced). We then need to know current
to convert that
to true wind (ground referenced).
The only wind we can directly measure from the boat is Apparent Wind. Leeway is not usually measured, unless you have a fancy multi-axis ultrasonic water-speed transducer (and I've never seen one of these myself). Leeway corrections can be made based on the observed angle of your wake, or calculations based on measured heel and known boat characteristics. Leeway can also be estimated from AWS/AWA/STW, and generic fudge-factor.
Many systems just figuratively throw up their hands ignore leeway, but that will result in inaccuracies that can be significant when close-hauled. For most of us that's good enough. If you are designing the next America's Cup boat you will want accurate data, but fortunately for most of us these numbers are merely a fun distraction.
The only reason it might matter here is if we are comparing the performance of different boats. The varieties of measurement methodology can result is significantly different numbers. Also fortunately for most here, these inaccuracies are most pronounced when sailing close-hauled, and that's a point of sail that most cruisers try to avoid on long passages.
So like many things, the closer you look the more complicated it becomes...