Planing and non-planing sailboards ...
I always like analogies that involve sailboards because it is one aspect of sailing that I really miss.
Yes, they are a planing hull design, but when planing, you would never have the centerboard down. In fact, short boards which are ONLY meant to be sailed on plane, don't even have a centerboard. Only long boards of the old design were equipped with a centerboard (I'm not even sure they make those designs any more). The newer designs of boards with a high volume are much wider, so that they can be sailed on plane with a huge sail in low-wind conditions. The older long boards (high volume) basically planed only in hi-wind, and were sailed as a displacement hull in low-wind. So the centerboard would be kicked-up when planing, and lowered when sub-planing.
That said, when planing, the board is NOT ENTIRELY steered by the position of the mast and rig. MOST of the steering is done by pressuring the rail of the board with your feet. If you notice hi-wind sailing, the rig is raked all the way back, with the foot of the sail basically on top of the board. The angle of the mast is raked back to an angle that is visually about 60 degrees or more, yet the board isn't pointing into the wind and has no weather helm. When sailing on plane, you can pressure the windward rail to point the board up, and once it is in the direction you want, the board has to be flattened with your feet to maintain the direction. Raking the mast back won't have any affect. When gybing downwind, the windsurfer basically stands up and pressures the leeward rail, carving the turn like a water ski or a snow ski. It's true that the mast and rig is then positioned forward, but that's not what is causing the affect in the turn.
A sub-planing long board can similarly be turned by pressuring the rails, but in the opposite direction. You turn the board upwind by pressuring the lee rail. and you turn downwind by pressuring the windward rail, and if there is a centerboard and it is down, it accentuates the affect.
It's true that all beginning windsurfers are taught that the board is turned by positioning the rake of the mast forward to gybe and back to turn upwind. But these are just the beginner techniques, that lose most of its validity as the speed dials up and the skill of the windsurfer improves.
What is interesting to note is that even a planing sailboard can develop a very bad case of weather helm when the rig is poorly tuned and the technique of the windsurfer is not correct. The interesting thing about windsurfing rigs is that even though adjustments are VERY small (and not easily made on the water), tuning the rig is of utmost importance. A poorly tuned rig will exhaust you in the same conditions that the exact same rig will feel light as a feather when tuned correctly, and the increments are barely perceptible. I've been sailing when the rig feels like lead, and my front leg is exhausted by pushing on the rail to keep the board from rounding up. Go back to shore and put in a half-inch of downhaul, flatten the battens, re-position the harness lines (which you can do on the water) and maybe a little outhaul to flatten the leech and voila! The board tracks exactly the way you want with no pressure on the front foot, and the rig feels like it is floating in air (basically which it is)!
It should also be noted that the position of the feet also does not affect the direction of the board when the rig is properly balanced. Footstraps are mounted all the way back on the board, the farther back the better for speed. Climbing into the footstraps when planing does not push the stern leeward as you would intuitively think.
So, I'm agreeing that the rake of the mast on a sailboat probably has a very minimal affect on weather helm or lee helm. It's the shape and trim of the sails that make all the difference!
