Carl,

are you sure flow around a catamaran hull is laminar? Perhaps in perfectly flat water, but in any kind of waves?
I asked around about finish on foils some time ago, and had a very credible source claim a 600 grit finish was good enough for the speed range between 10-14 knots. This is the range cats mostly sail in around here, so that is what we used. My source had done a tank test and 600 grit was the conclusion. I dont see why finish on the hulls should demand more than the foils?