Rudders & plates along centreline between hulls on Cats

I had to come back on this one myself when realising what a daft impression it might make in its present form.

I'm new at this forum stuff - thats my excuse and I'm sticking to it.

I wrote:- Can anyone explain why on catamarans, rudders and plates are not fitted along the center line between the hulls, but on each hull.

I was thinking of the effects of this arrangement on the physics of sailing rather than the obvious structural limitations of mounting such an arrangement particularly on smaller craft without decks or necelles.

I was also thinking about model radio controlled cats where operating plates in hulls when tacking means extra controls are required


thanks