Interesting thread, although it seems like it`s gone off the rails a bit. The fastest my beach cat has ever gone is 78 knots, or 90,06mph, or 145km/h, whatever you prefer.
It was on it`s trailer at the time, behind my truck.
I find it difficult to believe Frenchie that the fastest a Tornado has ever been timed over a 500m course was at around 22 knots, I know a Tornado is quicker than my 16ft
beach cat by a long way, so based on this info I can assume that the fastest my cat can go is about 18 knots.
Looking at the WSSC speed-sailing records I find that in 1977 Derk Thijs sailed a standard Windglider sailboard over the same timed course at an average speed of 19,1 knots.
Anyone who has ever seen a standard Windglider sailboard from that era will know without a doubt that a modern beach cat is capable of going faster than that - If you don`t
agree, bring your Windglider to the next cat regatta & prove your point in flat water on a broad reach. It won`t be pretty. If the Windglider wins, let me know & I`ll go back to sailing
standard one-design Windsurfers with soft sails & no footstraps.
You can take all the mathematical formulas you like & test in a laboratory all you like, the answers lie only down a 500m course in flat water with a stopwatch at either end.

Cheers
Steve