I claim the ornamental design for a boat stabilizing system, as shown and described.
FIG. 1 is a perspective view of a water system, showing my new design in a deployed position;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a right-side elevational view thereof;
FIG. 5 is a left-side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a perspective view thereof, illustrated in a stowed position; and,
FIG. 9 is a rear elevational view of FIG. 8.
The broken lines showing a boat and another boat stabilizing system in FIGS. 8 and 9 depict environmental matter and form no part of the claimed design.