Boat slip cover systems are provided for affixing to piers having a plurality of slips with closed and open ends, and first and second sides. Each boat slip cover includes a flexible canopy. Fixed supports for a first end of the canopy are disposed about the closed end of the slip, at least one extending upward from and perpendicular to the pier surface, and at least one extending upward from and angular to the pier surface. Rotating supports are disposed along each side of the slip and extend upward from the pier. Telescoping joints are disposed along each rotating support for their extension or retraction. A winch device is further provided for manual positioning. A convertible pier cover includes various retractable boat slip covers, valley portions extending between adjacent boat slip covers and forming an attachment on each side to an adjacent boat canopy, and a central aisle canopy.