Sorry guys, don't quite know how I achieved this, it was supposed to be in the Records thread!
While it is interesting to compare windspeed versus groundspeed, if you do any research on aero, you will not go very deeply before you discover that the research papers do not use windspeed at all in uncorrected form.
ie there is a correction applied for moisture content, atmospheric pressure,altitude etc. The resultant is "slugs". This is what is used for all the ratio calculations. (lift/drag etc)
It also explains why a given yacht in differing parts of the world can get different results. It was once shown to me that a very large keelboat (60+ ft) reduced from #1 headsail to #2 in 12 knots over the deck in Auckland harbour. The yacht then went to race in Hawaii, and they could carry the exact same sail (#1) to 18 knots over the deck.
In a nutshell, if you say (for example) "I did 65km/hr in my Blowie in 15km/hr of wind", in my book that is meritorious, but I now want to know about the surface, and what the altitude was.
We all know that salt, dry lake, beach, tarmac,grass, etc have differing drag. The Land speed record guys (automotive type) choose their venues to give best results, and I am told Bonneville is like driving on tiny marbles! But it is high!
The dry lake in Bolivia is at about 4000 metres with an average windspeed of around 40mph but not a lot of density, therefore less drag and much less capsize force. Just a bit expensive to get a yacht to!
