The ornamental design for an inflatabletowable, as shown and described.
FIG. 1 is a perspective view of the inflatable towable;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a left side elevational view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken-lines of the FIGS. 1-7 depict handles, attachments of the handles on the inflatable towable, a bottom surface of the inflatable towable, and a bottom rear surface of the inflatable towable. These broken line features are depicted for illustrative purposes, and form no part of the claimed design.