I claim the ornamental design for a adjustable boat tower canopy, as shown and described.
FIG. 1 is a perspective view of a adjustable boat tower canopy, showing the new design having adjustable legs and a canopy;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left-side elevational view thereof, the right-side elevational view being a mirror image thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is an alternate perspective view thereof, illustrated in a raised position above a ski boat tower.
The broken lines showing a ski boat tower in the figures represent environmental matter with the design in use, and form no part of the claimed design.