"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."

I find this quite surprising, as I believe 16knots is really easy for a spinnaker-equipped beachcat in the right conditions. I don`t know the Nacra 5.2, but I believe the Taipan 5.7 should do 20knots easily in 15-18knots of wind with a spinnaker up. In defence of my theory, I have sailed my Mosquito 16ft with spinnaker at 16.4knots on GPS in 12knots of wind with crew to leeward, so I think 18knots should be acchievable on a 4,9metre cat, a 5,2m cat should go a bit faster than that, and as the cat gets bigger, it should get faster, if Playstation is anything to go by.
What I do know from windsurfing with a GPS though, is that when you approach the speed at which your craft is "maxed out" you will have to work extremely hard and possibly do a lot of modifications to extract another knot out of it. I sat on 27knots as my ultimate top speed with the board I had for two years, and could reach it almost every time I sailed, but just couldn`t beat 27.4knots, in fact I did this exact speed so consistently that I was beginning to think my GPS had a fault. I then got a faster board and broke 30knots the first time I sailed it, now I`m reaching 32 on a regular basis, but once again I am approaching the limit of my equipment.
What I also know about the sensation of sailing at 25knots is that it is going to be extremely difficult to acchieve this on any beachcat design, regardless of any marketing brochure claims. I wish Warbird lots of luck and success with his efforts though, but I think some design modifications might be necessary to get there, and possibly some large ones. I would look at T-foil rudders, and possibly adding bruce-foil type daggerboards in front of the main beam to assist in anti-dive. These could even be laminated onto the outer skin of the hull on the chined surface, but the internal hull framing would have to be beefed up to support them. The biggest modification I would look at though is to mount the rig on the leeward hull, this would get the boat sailing flatter as warbird suggests, and get his weight and the weight of the weather hull further from the rig. He could then also experiment with canting it to weather, in much the same way as sailrocket is doing (www.sailrocket.com) Perhaps the scientists on this site will have a good laugh, but I think that would get more speed out of the boat. Of course that might also fall outside of what warbird is trying to acchieve, as it won`t be a general use sailing craft anymore, in that you would battle to sail it back upwind to the start of a speed course. Either way, I`ll be watching the progress of this rather interesting project, so please keep posting your findings and results.