Here is a well informed article on hull speed calculation from the boat design forum

http://www.boatdesign.net/forums/showthread.php?t=1220
It makes the point that you can go faster than the speed calculated using the LWL formulae, but it just chews up a lot more energy than is efficient.

His main point is that the formula actually calculates the speeds at which the bow wave is the length of the boat, and does not calculate the maximum speed attainable by the hull

**Quote:**

This is not a law on the maximum attainable speed but only the formula giving the hull speed at which the created wave length equals the hull length on the waterline. If it is a sailing vessel then the boat speed is quite obvious but if the boat is powered then a propeller travels through the water at the speed of advance. The speed of advance is the hull speed times (1 – Taylor’s wake) so it is nearly always less than the hull speed.

Lots of interesting info about correctly sizing a motor as well