Close there m8, here is another rather crude drawing
A cam may lessen the strain more so than a sliding tray, unless there was a passive hydraulic cylinder assist that could be used like a steering stabilizer? If the pivot point is about 1/3 back from the leading edge all the way down through the length of the rudder whereby the front tabs extruding out the front in the bottom half will assist with the water pressure when the brake is applied offering some measure of balance, depicted somewhat in the drawing, hope it makes sense. As far as max force on the steering servo I would be inclined to leave that as the weak point in the event the system was taxed too much (where do you want it to break if it needs to), it shouldn't be much more force than a hard bank maneuver on a standard rudder if they are only being splayed out to about 15 degree's or so. If I could only take the image in my head and transpose it to paper
, we all have our challenge's I guess, cheers
