If you're looking for an outrigger type of hydro, and you don't mind parting with a few quid (about £20) for the plans, I'm with Webby. The Firefighters are well proven (and well race proven), and you can download the plans as soon as you pay with PayPal. Tom Moorehouse also runs the forum which Webby mentioned, and seems like a thoroughly decent sort.
The one you would potentially want is the Firefighter Gas. It doesn't seem to appear if you click the boat plans link, but put firefighter gas in the search box, et Voila.......
Not sure if you're looking for something quite that fast though. I don't think you'd be wanting to run one of those at our usual Sunday venue. I'm guessing that you should be able to get something around 90MpH out of a gas Firefighter - probably more if you worked at it.