The ornamental design for a boat, as shown and described.
FIG. 1 is a perspective front view of a boat showing my new design;
FIG. 2 is a perspective rear view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a front view thereof;
FIG. 7 is a rear view thereof; and,
FIG. 8 is a bottom view thereof.
Gray scale images of a boat are shown in the figures. The contrast in gray scale represents a contrast in appearance only and does not represent any particular color, material, texture or finish.