catamaran

[xieme]

i am doing my final year project, designing a catamaran passenger ferry.
passanger capacity: 250
speed:35-40knots

i found a parent vessl that can fit 250 passenger.
i have the dimension of the parent vessel but i cannot just take that vessel dimension. i need some formula to help me justify how i arrive at the dimension. i was thinking of just using its' length 30.4m and the rest i will use formula to calculate. i have search the web for a month but there isn't any information on how to calculate the rest of the dimension. from what i know high speed catamaran cannot use conventional formula to calculate the dimension. pls help me