The needed power mainly depends of the displacement
Most of the production catamarans have a ratio of 6 to 7 hp per 1000kg maximum displacement
, or 8 to 10 hp per 1000kg lightship weight, and this is rather on the high side. This is the total for both engines.
speed is the limit over which the energy needed to displace the yacht is considered to increase dramatically. But the 1.34 *squareroot(waterline*length) limit was calculated by Froude for boats typically having a length:beam ratio around 4:1 (monohulls), and it is of much less importance with multihulls. See explanation here