is this the type of rough water you mean
if so you need one of these,
I sail solely in the ocean in WA, which if you've sailed here is as choppy & swell ridden as you like..
Over the years I've sailed many slalom and freeride and wave boards, last year or so I've been on a Patrik 100L Slalom..which I highly rate in the these conditions for comfort and speed in these conditions...
..that is until I got on the Patrik FreestyleWave 102L! This board is now my go to board, as it has nearly the same top-end speed as the Slalom (i know it sounds unbelievable), but so much more forgiving and fun in the open ocean...loves to pop if you want jumping, carves jybes like a dream, and gets up and goes like the clappers!
This board is unreal!! I've had friends try it and are blown away by it...particularly the speed of it!
GO try one out for yourself...you wont be disappointed. (I'm 94kgs, and ride it in anything from 16-25 kts with waves sails or freeride sails)