A jack plate (9) moveable upwardly and downwardly between various positions has a trim tab (28) disposed on a fixed portion (10) of the jack plate near the base of the transom (11) of a boat. The moveable portion (12) of the jack plate has a push cap (44) that, at a pickup position of the jack plate, pushes a rod (43) which rotates a lever (38) to move an arm (33) to push the trim tab (28) into an operative position aft of and below the hull of the boat. Above the pickup position, the push cap does not contact the rod; a return spring (50) causes the trim tab (28) to rotate upwardly, into a position where it is ineffective.