I investigated ackermann angles on Mozzy number two, it made no differance. Point the rudders straight down the centreline of the hulls after making sure they are square, line them up with the centreboards too.

To test it I angled the tiller part of the rudder stock inwards so the blade angles would change, relative to each other, as the crossbar was moved. It's a simple formula I found on the internet somewhere, it made no difference, I believe, because,
1, There is plenty of slip (water) between the rudders unlike car wheels which usually have good traction.
2, Mozzy's aren't very wide, might be noticeable on a Tornado.
3, Often when tacking is initiated, where the ackermann angle might have an effect, only one hull is in the water further reducing the benefit.