A trim tab shape control system for a boat with a transom according to an embodiment of the present invention includes a flexible plate and a trim tab control system. The flexible plate has a forward end attached to the transom, a rearward end, and an operative bottom surface. The trim tab control system includes a first force mechanism that is attached near the rearward end of the flexible plate and at least one second force mechanism interfacing the flexible plate between the transom and the first force mechanism. The force mechanisms are operative to deflect the operative bottom surface of the flexible plate in a controlled curve while in an up position, where the plate retains a shape in a down position which varies with force applied by the first and second force mechanisms and the operating conditions of the boat.