These are claimed to be true displacement hulls. The hull speed (most fuel-efficient speed) of a displacement hull is C times the sq root of the waterline length, for C somewhere between 1.2 and 1.7 depending on the authority, length in feet and speed in knots. This means a hull speed of 30 knots requires a LWL of around 450 feet, 50 kts a quarter of a mile. I believe that website is a complex practical joke.