The ornamental design for an adjustable boatchair, as shown and described.
FIG. 1 is rear perspective view showing the features of the adjustable boat
chair with the cushion in an exploded condition; and,
FIG. 2 is a rear perspective view showing the features of the adjustable
boat chair with the cushion in the installed condition.
The left side of the adjustable boat chair is a mirror image of that shown
in FIGS. 1 and 2. The portions of the adjustable boat chair as seen from
the front which are not shown in the drawing views form no part of the
claimed design.