First of all, my earlier post was more or less a brief summary of a few pages in my Textbook about Hydrodynamics on foils and ships (I'm a student at the Department of Marine Technology here in Norway, civ.ing degree), so that text is not false.

Erice, I wouldn't be too suprised of your top speed not being higher. Or, put in other words, 16+ knots on a Nacra 5.2 is fast! My dad and I sail a Taipan 5.7, which really is a fast cat (rated faster than F18s for instance), and we have never logged a better top speed than 19.7 knots. We are both certain that that particular blast isn't our fastest ever, so we consider our top speed as being just above 20 knots. This was done when a big puff(I'm guessing around 10 m/s) hit the boat, me out on the trap, dad inside on the helm, no spi up. No doubt, a better and more experienced crew could probably yank a couple of knots more out of the boat, but not a whole lot.

As for the 18ft skiffs, according to Frank Beathwait those monsters topped out at more than 30 knots in big winds and sailing with small rigs. There's a spectacular picture of a skiff screaming along in crazy conditions in his book. Around a course a Tornado would outsail them, as for sheer top speed however, I think the skiffs are way faster.