My rudders were as per HP plans , one way NACA foil shape. Easy to make the shape with foam and using the saw cut method. Able to get nice and smooth. Even put 400grit sandpaper to give mirror polish.

The balance way sorted out by a slight rake forward, ie. Rudder in down position was swung past vertical, so the forces on it balanced out.

Not sure how bi would go.

Am liking the idea of uni swing rudders and a bi centreboard. As from Ricks advice.

Doug