This formula is derived from Froude's law. Froude's law is derived from how the wave created by the bow interacts with the wave created by the stern, as well as how the waves are related to the boat speed. If these two waves interfere contructively, you will get a big increase in wave drag.
The Froude's number is given by:
Fn= Boat velocity/ "the root of" (g*length in waterline)
Typical Froude's numbers:
Type of boat------------length(m)------speed (kts)------Fn
As one can see the catamaran has a relatively very high Froudes number. These wessels are designed to carry people fast and safely between islands etc, and so that requires high speed, but also a not too big vessel that easily can be handled in port. The answer: Long, slender hulls in the water line. These hulls creates alot less wave drag as they "pierce" through the water. The slenderness however means loss of stability, hence why one have to have more than one hull.
When asked of what the max speed for a high performance beach cat was, my hydrodynamic prof. simply said: "there's no such thing as a theoretical max speed. If you have enough power, you can always go faster."
That been said, personally, I think the Tornado blast contest already mentioned here gives a pretty good estimate. Tornados are wide and have alot of power. In addition, the record set in the speed contest, was done by a highly skilled crew.
