From the Starboard forum http://www.starboard-windsurfing.com/forum/showthread.php?t=3968 The sailpadd.xls calculator Is it all that simple? (does not apply to Isonics, apparently)
That calculator looks pretty right to me. The wind speed it specifies for each sail is, for me, the minimum required to get planing without pumping. My weight varies quite a lot. In the last 18 months I have been anywhere from 83kg to 103kg and the calculator seems to be spot on.
It says that dropping from 95 to 75 kg makes my 7 meter sail plane at 14 instead of 18 knots. That means every knot improvement needs a 5 kg weight reduction. That means giving up beer forever :(
