Your diagram is how I plan to pull them down but unfortionatly you cant make a board floaty enough to self raise completely as they are already foam filled but to keep them strong the fiberglass makes them to heavy.
Put a board in the water by itself and it floats happily.
Lift one end of the board so its now vertical and half the board dissapears under water to remain afloat so I definatly need a good rasing system to fully retract the board. I need a good frictionless packing for inside the casing to stop the board from jamming. A 3 point roller system might work but it gets too fiddley and I think it would need a complicated mounting to align the rollers. So Id like to follow the K.I.S.S rule. I need the best frictionless carpet or padding. I will buy a few samples and experiment wet and dry.