The present invention relates to a retractable canopy structure adapted to be used in conjunction with the canopy structure on a boat's existing T-top tubular frame near the level of the existing canopy. The canopy frame structure comprises two longitudinally aligned, telescoping members with at least one transverse, telescoping frame member disposed between the two longitudinal members to prevent the canopy from collapsing when under tension. The canopy frame structure is disposed onto the existing T-top frame using a mounting assembly comprising of a grommet adapted to be placed between two frame members and wrapped with an adjustable strap. The canopy and telescoping frame components are designed to be adaptable to various T-top canopy widths, and can be extended to various lengths to increase the amount of available canopy shade area while in the mounted position on the boat's existing T-top.